path: root/man1p/pax.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "PAX" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" pax 
.SH NAME
pax \- portable archive interchange
.SH SYNOPSIS
.LP
\fBpax\fP \fB[\fP\fB-cdnv\fP\fB][\fP\fB-H|-L\fP\fB][\fP\fB-f\fP \fIarchive\fP\fB][\fP\fB-s\fP
\fIreplstr\fP\fB]\fP\fB...\fP\fB[\fP\fIpattern\fP\fB...\fP\fB]\fP\fB
.br
.sp
pax -r\fP\fB[\fP\fB-cdiknuv\fP\fB][\fP\fB-H|-L\fP\fB][\fP\fB-f\fP
\fIarchive\fP\fB][\fP\fB-o\fP
\fIoptions\fP\fB]\fP\fB...\fP\fB[\fP\fB-p\fP \fIstring\fP\fB]\fP\fB...
.br
\ \ \ \ \ \ \fP \fB[\fP\fB-s\fP
\fIreplstr\fP\fB]\fP\fB...\fP\fB[\fP\fIpattern\fP\fB...\fP\fB]\fP\fB
.br
.sp
pax -w\fP\fB[\fP\fB-dituvX\fP\fB][\fP\fB-H|-L\fP\fB][\fP\fB-b\fP
\fIblocksize\fP\fB][[\fP\fB-a\fP\fB][\fP\fB-f\fP \fIarchive\fP\fB][\fP\fB-o\fP
\fIoptions\fP\fB]\fP\fB...
.br
\ \ \ \ \ \ \fP \fB[\fP\fB-s\fP \fIreplstr\fP\fB]\fP\fB...\fP\fB[\fP\fB-x\fP
\fIformat\fP\fB][\fP\fIfile\fP\fB...\fP\fB]\fP\fB
.br
.sp
pax -r -w\fP\fB[\fP\fB-diklntuvX\fP\fB][\fP\fB-H|-L\fP\fB][\fP\fB-p\fP
\fIstring\fP\fB]\fP\fB...\fP\fB[\fP\fB-s\fP \fIreplstr\fP\fB]\fP\fB...
.br
\ \ \ \ \ \ \fP \fB[\fP\fIfile\fP\fB...\fP\fB]\fP \fIdirectory\fP\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIpax\fP utility shall read, write, and write lists of the members
of archive files and copy directory hierarchies. A
variety of archive formats shall be supported; see the \fB-x\fP \fIformat\fP
option.
.LP
The action to be taken depends on the presence of the \fB-r\fP and
\fB-w\fP options. The four combinations of \fB-r\fP and
\fB-w\fP are referred to as the four modes of operation: \fBlist\fP,
\fBread\fP, \fBwrite\fP, and \fBcopy\fP modes,
corresponding respectively to the four forms shown in the SYNOPSIS
section.
.TP 7
\fBlist\fP
In \fBlist\fP mode (when neither \fB-r\fP nor \fB-w\fP are specified),
\fIpax\fP shall write the names of the members of
the archive file read from the standard input, with pathnames matching
the specified patterns, to standard output. If a named file
is of type directory, the file hierarchy rooted at that file shall
be listed as well.
.TP 7
\fBread\fP
In \fBread\fP mode (when \fB-r\fP is specified, but \fB-w\fP is not),
\fIpax\fP shall extract the members of the archive
file read from the standard input, with pathnames matching the specified
patterns. If an extracted file is of type directory, the
file hierarchy rooted at that file shall be extracted as well. The
extracted files shall be created performing pathname resolution
with the directory in which \fIpax\fP was invoked as the current working
directory. 
.LP
If an attempt is made to extract a directory when the directory already
exists, this shall not be considered an error. If an
attempt is made to extract a FIFO when the FIFO already exists, this
shall not be considered an error.
.LP
The ownership, access, and modification times, and file mode of the
restored files are discussed under the \fB-p\fP option.
.TP 7
\fBwrite\fP
In \fBwrite\fP mode (when \fB-w\fP is specified, but \fB-r\fP is not),
\fIpax\fP shall write the contents of the
\fIfile\fP operands to the standard output in an archive format. If
no \fIfile\fP operands are specified, a list of files to
copy, one per line, shall be read from the standard input. A file
of type directory shall include all of the files in the file
hierarchy rooted at the file.
.TP 7
\fBcopy\fP
In \fBcopy\fP mode (when both \fB-r\fP and \fB-w\fP are specified),
\fIpax\fP shall copy the \fIfile\fP operands to the
destination directory. 
.LP
If no \fIfile\fP operands are specified, a list of files to copy,
one per line, shall be read from the standard input. A file
of type directory shall include all of the files in the file hierarchy
rooted at the file.
.LP
The effect of the \fBcopy\fP shall be as if the copied files were
written to an archive file and then subsequently extracted,
except that there may be hard links between the original and the copied
files. If the destination directory is a subdirectory of
one of the files to be copied, the results are unspecified. If the
destination directory is a file of a type not defined by the
System Interfaces volume of IEEE\ Std\ 1003.1-2001, the results are
implementation-defined; otherwise, it shall be an error
for the file named by the \fIdirectory\fP operand not to exist, not
be writable by the user, or not be a file of type
directory.
.sp
.LP
In \fBread\fP or \fBcopy\fP modes, if intermediate directories are
necessary to extract an archive member, \fIpax\fP shall
perform actions equivalent to the \fImkdir\fP() function defined in
the System Interfaces
volume of IEEE\ Std\ 1003.1-2001, called with the following arguments:
.IP " *" 3
The intermediate directory used as the \fIpath\fP argument
.LP
.IP " *" 3
The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and S_IRWXO
as the \fImode\fP argument
.LP
.LP
If any specified \fIpattern\fP or \fIfile\fP operands are not matched
by at least one file or archive member, \fIpax\fP shall
write a diagnostic message to standard error for each one that did
not match and exit with a non-zero exit status.
.LP
The archive formats described in the EXTENDED DESCRIPTION section
shall be automatically detected on input. The default output
archive format shall be implementation-defined.
.LP
A single archive can span multiple files. The \fIpax\fP utility shall
determine, in an implementation-defined manner, what file
to read or write as the next file.
.LP
If the selected archive format supports the specification of linked
files, it shall be an error if these files cannot be linked
when the archive is extracted. For archive formats that do not store
file contents with each name that causes a hard link, if the
file that contains the data is not extracted during this \fIpax\fP
session, either the data shall be restored from the original
file, or a diagnostic message shall be displayed with the name of
a file that can be used to extract the data. In traversing
directories, \fIpax\fP shall detect infinite loops; that is, entering
a previously visited directory that is an ancestor of the
last file visited. When it detects an infinite loop, \fIpax\fP shall
write a diagnostic message to standard error and shall
terminate.
.SH OPTIONS
.LP
The \fIpax\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines,
except that the order of presentation of the
\fB-o\fP, \fB-p\fP, and \fB-s\fP options is significant.
.LP
The following options shall be supported:
.TP 7
\fB-r\fP
Read an archive file from standard input.
.TP 7
\fB-w\fP
Write files to the standard output in the specified archive format.
.TP 7
\fB-a\fP
Append files to the end of the archive. It is implementation-defined
which devices on the system support appending. Additional
file formats unspecified by this volume of IEEE\ Std\ 1003.1-2001
may impose restrictions on appending.
.TP 7
\fB-b\ \fP \fIblocksize\fP
Block the output at a positive decimal integer number of bytes per
write to the archive file. Devices and archive formats may
impose restrictions on blocking. Blocking shall be automatically determined
on input. Conforming applications shall not specify a
\fIblocksize\fP value larger than 32256. Default blocking when creating
archives depends on the archive format. (See the \fB-x\fP
option below.)
.TP 7
\fB-c\fP
Match all file or archive members except those specified by the \fIpattern\fP
or \fIfile\fP operands.
.TP 7
\fB-d\fP
Cause files of type directory being copied or archived or archive
members of type directory being extracted or listed to match
only the file or archive member itself and not the file hierarchy
rooted at the file.
.TP 7
\fB-f\ \fP \fIarchive\fP
Specify the pathname of the input or output archive, overriding the
default standard input (in \fBlist\fP or \fBread\fP
modes) or standard output ( \fBwrite\fP mode).
.TP 7
\fB-H\fP
If a symbolic link referencing a file of type directory is specified
on the command line, \fIpax\fP shall archive the file
hierarchy rooted in the file referenced by the link, using the name
of the link as the root of the file hierarchy. Otherwise, if a
symbolic link referencing a file of any other file type which \fIpax\fP
can normally archive is specified on the command line,
then \fIpax\fP shall archive the file referenced by the link, using
the name of the link. The default behavior shall be to archive
the symbolic link itself.
.TP 7
\fB-i\fP
Interactively rename files or archive members. For each archive member
matching a \fIpattern\fP operand or file matching a
\fIfile\fP operand, a prompt shall be written to the file \fB/dev/tty\fP.
The prompt shall contain the name of the file or
archive member, but the format is otherwise unspecified. A line shall
then be read from \fB/dev/tty\fP. If this line is blank, the
file or archive member shall be skipped. If this line consists of
a single period, the file or archive member shall be processed
with no modification to its name. Otherwise, its name shall be replaced
with the contents of the line. The \fIpax\fP utility shall
immediately exit with a non-zero exit status if end-of-file is encountered
when reading a response or if \fB/dev/tty\fP cannot be
opened for reading and writing. 
.LP
The results of extracting a hard link to a file that has been renamed
during extraction are unspecified.
.TP 7
\fB-k\fP
Prevent the overwriting of existing files.
.TP 7
\fB-l\fP
(The letter ell.) In \fBcopy\fP mode, hard links shall be made between
the source and destination file hierarchies whenever
possible. If specified in conjunction with \fB-H\fP or \fB-L\fP, when
a symbolic link is encountered, the hard link created in
the destination file hierarchy shall be to the file referenced by
the symbolic link. If specified when neither \fB-H\fP nor
\fB-L\fP is specified, when a symbolic link is encountered, the implementation
shall create a hard link to the symbolic link in
the source file hierarchy or copy the symbolic link to the destination.
.TP 7
\fB-L\fP
If a symbolic link referencing a file of type directory is specified
on the command line or encountered during the traversal of
a file hierarchy, \fIpax\fP shall archive the file hierarchy rooted
in the file referenced by the link, using the name of the link
as the root of the file hierarchy. Otherwise, if a symbolic link referencing
a file of any other file type which \fIpax\fP can
normally archive is specified on the command line or encountered during
the traversal of a file hierarchy, \fIpax\fP shall archive
the file referenced by the link, using the name of the link. The default
behavior shall be to archive the symbolic link
itself.
.TP 7
\fB-n\fP
Select the first archive member that matches each \fIpattern\fP operand.
No more than one archive member shall be matched for
each pattern (although members of type directory shall still match
the file hierarchy rooted at that file).
.TP 7
\fB-o\ \fP \fIoptions\fP
Provide information to the implementation to modify the algorithm
for extracting or writing files. The value of \fIoptions\fP
shall consist of one or more comma-separated keywords of the form:
.sp
.RS
.nf

\fIkeyword\fP\fB[[\fP\fB:\fP\fB]\fP\fB=\fP\fIvalue\fP\fB][\fP\fB,\fP\fIkeyword\fP\fB[[\fP\fB:\fP\fB]\fP\fB=\fP\fIvalue\fP\fB]\fP\fB, ...\fP\fB]\fP
.fi
.RE
.LP
Some keywords apply only to certain file formats, as indicated with
each description. Use of keywords that are inapplicable to
the file format being processed produces undefined results.
.LP
Keywords in the \fIoptions\fP argument shall be a string that would
be a valid portable filename as described in the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, Section 3.276, Portable
Filename Character Set. 
.TP 7
\fBNote:\fP
.RS
Keywords are not expected to be filenames, merely to follow the same
character composition rules as portable filenames.
.RE
.sp
.LP
Keywords can be preceded with white space. The \fIvalue\fP field shall
consist of zero or more characters; within \fIvalue\fP,
the application shall precede any literal comma with a backslash,
which shall be ignored, but preserves the comma as part of
\fIvalue\fP. A comma as the final character, or a comma followed solely
by white space as the final characters, in \fIoptions\fP
shall be ignored. Multiple \fB-o\fP options can be specified; if keywords
given to these multiple \fB-o\fP options conflict, the
keywords and values appearing later in command line sequence shall
take precedence and the earlier shall be silently ignored. The
following keyword values of \fIoptions\fP shall be supported for the
file formats as indicated:
.TP 7
\fBdelete\fP=\fIpattern\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fBpax\fP format.) When used in \fBwrite\fP
or \fBcopy\fP mode, \fIpax\fP shall omit from
extended header records that it produces any keywords matching the
string pattern. When used in \fBread\fP or \fBlist\fP mode,
\fIpax\fP shall ignore any keywords matching the string pattern in
the extended header records. In both cases, matching shall be
performed using the pattern matching notation described in \fIPatterns
Matching a Single
Character\fP and \fIPatterns Matching Multiple Characters\fP . For
example: 
.sp
.RS
.nf

\fB-o\fP \fBdelete\fP\fB=\fP\fIsecurity\fP\fB.*
\fP
.fi
.RE
.LP
would suppress security-related information. See pax Extended Header
for extended header record
keyword usage.
.RE
.TP 7
\fBexthdr.name\fP=\fIstring\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fBpax\fP format.) This keyword allows
user control over the name that is written into the
\fBustar\fP header blocks for the extended header produced under the
circumstances described in pax
Header Block . The name shall be the contents of \fIstring\fP, after
the following character substitutions have been made: 
.TS C
center; l lw(40).
\fB\fIstring\fP\fP	T{
.na
\fB\ \fP
.ad
T}
\fBIncludes:\fP	T{
.na
\fBReplaced By:\fP
.ad
T}
%d	T{
.na
The directory name of the file, equivalent to the result of the \fIdirname\fP utility on the translated pathname.
.ad
T}
%f	T{
.na
The filename of the file, equivalent to the result of the \fIbasename\fP utility on the translated pathname.
.ad
T}
%p	T{
.na
The process ID of the \fIpax\fP process.
.ad
T}
%%	T{
.na
A \fB'%'\fP character.
.ad
T}
.TE
.LP
Any other \fB'%'\fP characters in \fIstring\fP produce undefined results.
.LP
If no \fB-o\fP \fBexthdr.name=\fP \fIstring\fP is specified, \fIpax\fP
shall use the following default value:
.sp
.RS
.nf

\fB%d/PaxHeaders.%p/%f
\fP
.fi
.RE
.RE
.TP 7
\fBglobexthdr.name\fP=\fIstring\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fBpax\fP format.) When used in \fBwrite\fP
or \fBcopy\fP mode with the appropriate options,
\fIpax\fP shall create global extended header records with \fBustar\fP
header blocks that will be treated as regular files by
previous versions of \fIpax\fP. This keyword allows user control over
the name that is written into the \fBustar\fP header blocks
for global extended header records. The name shall be the contents
of string, after the following character substitutions have been
made: 
.TS C
center; l lw(40).
\fB\fIstring\fP\fP	T{
.na
\fB\ \fP
.ad
T}
\fBIncludes:\fP	T{
.na
\fBReplaced By:\fP
.ad
T}
%n	T{
.na
An integer that represents the sequence number of the global extended header record in the archive, starting at 1.
.ad
T}
%p	T{
.na
The process ID of the \fIpax\fP process.
.ad
T}
%%	T{
.na
A \fB'%'\fP character.
.ad
T}
.TE
.LP
Any other \fB'%'\fP characters in \fIstring\fP produce undefined results.
.LP
If no \fB-o\fP \fBglobexthdr.name=\fP \fIstring\fP is specified, \fIpax\fP
shall use the following default value:
.sp
.RS
.nf

\fB$TMPDIR/GlobalHead.%p.%n
\fP
.fi
.RE
.LP
where $ \fITMPDIR\fP represents the value of the \fITMPDIR\fP environment
variable. If \fITMPDIR\fP is not set, \fIpax\fP
shall use \fB/tmp\fP.
.RE
.TP 7
\fBinvalid\fP=\fIaction\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fBpax\fP format.) This keyword allows
user control over the action \fIpax\fP takes upon
encountering values in an extended header record that, in \fBread\fP
or \fBcopy\fP mode, are invalid in the destination hierarchy
or, in \fBlist\fP mode, cannot be written in the codeset and current
locale of the implementation. The following are invalid
values that shall be recognized by \fIpax\fP: 
.RS
.IP " *" 3
In \fBread\fP or \fBcopy\fP mode, a filename or link name that contains
character encodings invalid in the destination
hierarchy. (For example, the name may contain embedded NULs.)
.LP
.IP " *" 3
In \fBread\fP or \fBcopy\fP mode, a filename or link name that is
longer than the maximum allowed in the destination hierarchy
(for either a pathname component or the entire pathname).
.LP
.IP " *" 3
In \fBlist\fP mode, any character string value (filename, link name,
user name, and so on) that cannot be written in the
codeset and current locale of the implementation.
.LP
.RE
.LP
The following mutually-exclusive values of the \fIaction\fP argument
are supported:
.TP 7
\fBbypass\fP
.RS
In \fBread\fP or \fBcopy\fP mode, \fIpax\fP shall bypass the file,
causing no change to the destination hierarchy. In
\fBlist\fP mode, \fIpax\fP shall write all requested valid values
for the file, but its method for writing invalid values is
unspecified.
.RE
.TP 7
\fBrename\fP
.RS
In \fBread\fP or \fBcopy\fP mode, \fIpax\fP shall act as if the \fB-i\fP
option were in effect for each file with invalid
filename or link name values, allowing the user to provide a replacement
name interactively. In \fBlist\fP mode, \fIpax\fP shall
behave identically to the \fBbypass\fP action.
.RE
.TP 7
\fBUTF-8\fP
.RS
When used in \fBread\fP, \fBcopy\fP, or \fBlist\fP mode and a filename,
link name, owner name, or any other field in an
extended header record cannot be translated from the \fBpax\fP UTF-8
codeset format to the codeset and current locale of the
implementation, \fIpax\fP shall use the actual UTF-8 encoding for
the name.
.RE
.TP 7
\fBwrite\fP
.RS
In \fBread\fP or \fBcopy\fP mode, \fIpax\fP shall write the file,
translating or truncating the name, regardless of whether
this may overwrite an existing file with a valid name. In \fBlist\fP
mode, \fIpax\fP shall behave identically to the
\fBbypass\fP action.
.RE
.sp
.LP
If no \fB-o\fP \fBinvalid=\fP option is specified, \fIpax\fP shall
act as if \fB-o\fP \fBinvalid=\fP \fBbypass\fP were
specified. Any overwriting of existing files that may be allowed by
the \fB-o\fP \fBinvalid=\fP actions shall be subject to
permission ( \fB-p\fP) and modification time ( \fB-u\fP) restrictions,
and shall be suppressed if the \fB-k\fP option is also
specified.
.RE
.TP 7
\fBlinkdata\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fBpax\fP format.) In \fBwrite\fP
mode, \fIpax\fP shall write the contents of a file to the
archive even when that file is merely a hard link to a file whose
contents have already been written to the archive.
.RE
.TP 7
\fBlistopt\fP=\fIformat\fP
.RS
.sp
This keyword specifies the output format of the table of contents
produced when the \fB-v\fP option is specified in \fBlist\fP
mode. See List Mode Format Specifications . To avoid ambiguity, the
\fBlistopt=\fP \fIformat\fP
shall be the only or final \fBkeyword=\fP \fIvalue\fP pair in a \fB-o\fP
option-argument; all characters in the remainder of the
option-argument shall be considered part of the format string. When
multiple \fB-o\fP \fBlistopt=\fP \fIformat\fP options are
specified, the format strings shall be considered a single, concatenated
string, evaluated in command line order.
.RE
.TP 7
\fBtimes\fP
.RS
.sp
(Applicable only to the \fB-x\fP \fIpax\fP format.) When used in \fBwrite\fP
or \fBcopy\fP mode, \fIpax\fP shall include
\fBatime\fP, \fBctime\fP, and \fBmtime\fP extended header records
for each file. See pax Extended
Header File Times .
.RE
.sp
.LP
In addition to these keywords, if the \fB-x\fP \fIpax\fP format is
specified, any of the keywords and values defined in pax Extended
Header , including implementation extensions, can be used in \fB-o\fP
option-arguments,
in either of two modes:
.TP 7
\fBkeyword\fP=\fIvalue\fP
.RS
.sp
When used in \fBwrite\fP or \fBcopy\fP mode, these keyword/value pairs
shall be included at the beginning of the archive as
\fBtypeflag\fP \fBg\fP global extended header records. When used in
\fBread\fP or \fBlist\fP mode, these keyword/value pairs
shall act as if they had been at the beginning of the archive as \fBtypeflag\fP
\fBg\fP global extended header records.
.RE
.TP 7
\fBkeyword\fP:=\fIvalue\fP
.RS
.sp
When used in \fBwrite\fP or \fBcopy\fP mode, these keyword/value pairs
shall be included as records at the beginning of a
\fBtypeflag\fP \fBx\fP extended header for each file. (This shall
be equivalent to the equal-sign form except that it creates no
\fBtypeflag\fP \fBg\fP global extended header records.) When used
in \fBread\fP or \fBlist\fP mode, these keyword/value pairs
shall act as if they were included as records at the end of each extended
header; thus, they shall override any global or
file-specific extended header record keywords of the same names. For
example, in the command: 
.sp
.RS
.nf

\fBpax -r -o "
gname:=mygroup,
" <archive
\fP
.fi
.RE
.LP
the group name will be forced to a new value for all files read from
the archive.
.RE
.sp
.LP
The precedence of \fB-o\fP keywords over various fields in the archive
is described in pax Extended
Header Keyword Precedence .
.TP 7
\fB-p\ \fP \fIstring\fP
Specify one or more file characteristic options (privileges). The
\fIstring\fP option-argument shall be a string specifying
file characteristics to be retained or discarded on extraction. The
string shall consist of the specification characters \fBa\fP
, \fBe\fP , \fBm\fP , \fBo\fP , and \fBp\fP . Other implementation-defined
characters can be included. Multiple
characteristics can be concatenated within the same string and multiple
\fB-p\fP options can be specified. The meaning of the
specification characters are as follows: 
.TP 7
\fBa\fP
.RS
Do not preserve file access times.
.RE
.TP 7
\fBe\fP
.RS
Preserve the user ID, group ID, file mode bits (see the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, Section 3.168, File Mode Bits),
access time, modification time, and any other
implementation-defined file characteristics.
.RE
.TP 7
\fBm\fP
.RS
Do not preserve file modification times.
.RE
.TP 7
\fBo\fP
.RS
Preserve the user ID and group ID.
.RE
.TP 7
\fBp\fP
.RS
Preserve the file mode bits. Other implementation-defined file mode
attributes may be preserved.
.RE
.sp
.LP
In the preceding list, "preserve" indicates that an attribute stored
in the archive shall be given to the extracted file,
subject to the permissions of the invoking process. The access and
modification times of the file shall be preserved unless
otherwise specified with the \fB-p\fP option or not stored in the
archive. All attributes that are not preserved shall be
determined as part of the normal file creation action (see \fIFile
Read, Write, and
Creation\fP ).
.LP
If neither the \fBe\fP nor the \fBo\fP specification character is
specified, or the user ID and group ID are not preserved
for any reason, \fIpax\fP shall not set the S_ISUID and S_ISGID bits
of the file mode.
.LP
If the preservation of any of these items fails for any reason, \fIpax\fP
shall write a diagnostic message to standard error.
Failure to preserve these items shall affect the final exit status,
but shall not cause the extracted file to be deleted.
.LP
If file characteristic letters in any of the \fIstring\fP option-arguments
are duplicated or conflict with each other, the ones
given last shall take precedence. For example, if \fB-p\fP \fBeme\fP
is specified, file modification times are preserved.
.TP 7
\fB-s\ \fP \fIreplstr\fP
Modify file or archive member names named by \fIpattern\fP or \fIfile\fP
operands according to the substitution expression
\fIreplstr\fP, using the syntax of the \fIed\fP utility. The concepts
of "address" and
"line" are meaningless in the context of the \fIpax\fP utility, and
shall not be supplied. The format shall be: 
.sp
.RS
.nf

\fB-s /\fP\fIold\fP\fB/\fP\fInew\fP\fB/\fP\fB[\fP\fBgp\fP\fB]\fP
.fi
.RE
.LP
where as in \fIed\fP, \fIold\fP is a basic regular expression and
\fInew\fP can contain an
ampersand, \fB'\\n'\fP (where \fIn\fP is a digit) backreferences,
or subexpression matching. The \fIold\fP string shall also be
permitted to contain <newline>s.
.LP
Any non-null character can be used as a delimiter ( \fB'/'\fP shown
here). Multiple \fB-s\fP expressions can be specified;
the expressions shall be applied in the order specified, terminating
with the first successful substitution. The optional trailing
\fB'g'\fP is as defined in the \fIed\fP utility. The optional trailing
\fB'p'\fP shall
cause successful substitutions to be written to standard error. File
or archive member names that substitute to the empty string
shall be ignored when reading and writing archives.
.TP 7
\fB-t\fP
When reading files from the file system, and if the user has the permissions
required by \fIutime\fP() to do so, set the access time of each file
read to the access time that it had before
being read by \fIpax\fP.
.TP 7
\fB-u\fP
Ignore files that are older (having a less recent file modification
time) than a pre-existing file or archive member with the
same name. In \fBread\fP mode, an archive member with the same name
as a file in the file system shall be extracted if the archive
member is newer than the file. In \fBwrite\fP mode, an archive file
member with the same name as a file in the file system shall
be superseded if the file is newer than the archive member. If \fB-a\fP
is also specified, this is accomplished by appending to
the archive; otherwise, it is unspecified whether this is accomplished
by actual replacement in the archive or by appending to the
archive. In \fBcopy\fP mode, the file in the destination hierarchy
shall be replaced by the file in the source hierarchy or by a
link to the file in the source hierarchy if the file in the source
hierarchy is newer.
.TP 7
\fB-v\fP
In \fBlist\fP mode, produce a verbose table of contents (see the STDOUT
section). Otherwise, write archive member pathnames to
standard error (see the STDERR section).
.TP 7
\fB-x\ \fP \fIformat\fP
Specify the output archive format. The \fIpax\fP utility shall support
the following formats: 
.TP 7
\fBcpio\fP
.RS
The \fBcpio\fP interchange format; see the EXTENDED DESCRIPTION section.
The default \fIblocksize\fP for this format for
character special archive files shall be 5120. Implementations shall
support all \fIblocksize\fP values less than or equal to
32256 that are multiples of 512.
.RE
.TP 7
\fBpax\fP
.RS
The \fBpax\fP interchange format; see the EXTENDED DESCRIPTION section.
The default \fIblocksize\fP for this format for
character special archive files shall be 5120. Implementations shall
support all \fIblocksize\fP values less than or equal to
32256 that are multiples of 512.
.RE
.TP 7
\fBustar\fP
.RS
The \fBtar\fP interchange format; see the EXTENDED DESCRIPTION section.
The default \fIblocksize\fP for this format for
character special archive files shall be 10240. Implementations shall
support all \fIblocksize\fP values less than or equal to
32256 that are multiples of 512.
.RE
.sp
.LP
Implementation-defined formats shall specify a default block size
as well as any other block sizes supported for character
special archive files.
.LP
Any attempt to append to an archive file in a format different from
the existing archive format shall cause \fIpax\fP to exit
immediately with a non-zero exit status.
.LP
In \fBcopy\fP mode, if no \fB-x\fP format is specified, \fIpax\fP
shall behave as if \fB-x\fP \fIpax\fP were specified.
.TP 7
\fB-X\fP
When traversing the file hierarchy specified by a pathname, \fIpax\fP
shall not descend into directories that have a different
device ID ( \fIst_dev\fP; see the System Interfaces volume of IEEE\ Std\ 1003.1-2001,
\fIstat\fP()).
.sp
.LP
The options that operate on the names of files or archive members
( \fB-c\fP, \fB-i\fP, \fB-n\fP, \fB-s\fP, \fB-u\fP, and
\fB-v\fP) shall interact as follows. In \fBread\fP mode, the archive
members shall be selected based on the user-specified
\fIpattern\fP operands as modified by the \fB-c\fP, \fB-n\fP, and
\fB-u\fP options. Then, any \fB-s\fP and \fB-i\fP options
shall modify, in that order, the names of the selected files. The
\fB-v\fP option shall write names resulting from these
modifications.
.LP
In \fBwrite\fP mode, the files shall be selected based on the user-specified
pathnames as modified by the \fB-n\fP and
\fB-u\fP options. Then, any \fB-s\fP and \fB-i\fP options shall modify,
in that order, the names of these selected files. The
\fB-v\fP option shall write names resulting from these modifications.
.LP
If both the \fB-u\fP and \fB-n\fP options are specified, \fIpax\fP
shall not consider a file selected unless it is newer than
the file to which it is compared.
.SS List Mode Format Specifications
.LP
In \fBlist\fP mode with the \fB-o\fP \fBlistopt=\fP \fIformat\fP option,
the \fIformat\fP argument shall be applied for
each selected file. The \fIpax\fP utility shall append a <newline>
to the \fBlistopt\fP output for each selected file. The
\fIformat\fP argument shall be used as the \fIformat\fP string described
in the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Chapter 5, File Format Notation, with the
exceptions 1.
through 5. defined in the EXTENDED DESCRIPTION section of \fIprintf\fP,
plus the following
exceptions:
.TP 7
6.
The sequence ( \fIkeyword\fP) can occur before a format conversion
specifier. The conversion argument is defined by the value
of \fIkeyword\fP. The implementation shall support the following keywords:
.RS
.IP " *" 3
Any of the Field Name entries in ustar Header Block and Octet-Oriented
cpio
Archive Entry . The implementation may support the \fIcpio\fP keywords
without the leading \fBc_\fP in addition to the form
required by Values for cpio c_mode Field .
.LP
.IP " *" 3
Any keyword defined for the extended header in pax Extended Header
\&.
.LP
.IP " *" 3
Any keyword provided as an implementation-defined extension within
the extended header defined in pax Extended Header .
.LP
.RE
.LP
For example, the sequence \fB"%(charset)s"\fP is the string value
of the name of the character set in the extended
header.
.LP
The result of the keyword conversion argument shall be the value from
the applicable header field or extended header, without
any trailing NULs.
.LP
All keyword values used as conversion arguments shall be translated
from the UTF-8 encoding to the character set appropriate for
the local file system, user database, and so on, as applicable.
.TP 7
7.
An additional conversion specifier character, \fBT\fP , shall be used
to specify time formats. The \fBT\fP conversion
specifier character can be preceded by the sequence ( \fIkeyword=\fP
\fIsubformat\fP), where \fIsubformat\fP is a date format as
defined by \fIdate\fP operands. The default \fIkeyword\fP shall be
\fBmtime\fP and the
default subformat shall be: 
.sp
.RS
.nf

\fB%b %e %H:%M %Y
\fP
.fi
.RE
.TP 7
8.
An additional conversion specifier character, \fBM\fP , shall be used
to specify the file mode string as defined in \fIls\fP Standard Output.
If ( \fIkeyword\fP) is omitted, the \fBmode\fP keyword shall be used.
For
example, \fB%.1M\fP writes the single character corresponding to the
<\fIentry\ type\fP> field of the \fIls\fP \fB-l\fP command.
.TP 7
9.
An additional conversion specifier character, \fBD\fP , shall be used
to specify the device for block or special files, if
applicable, in an implementation-defined format. If not applicable,
and ( \fIkeyword\fP) is specified, then this conversion shall
be equivalent to \fB%(\fP\fIkeyword\fP\fB)u\fP. If not applicable,
and ( \fIkeyword\fP) is omitted, then this conversion
shall be equivalent to <space>.
.TP 7
10.
An additional conversion specifier character, \fBF\fP , shall be used
to specify a pathname. The \fBF\fP conversion
character can be preceded by a sequence of comma-separated keywords:
.sp
.RS
.nf

\fB(\fP\fIkeyword\fP\fB[\fP\fB,\fP\fIkeyword\fP\fB]\fP \fB... )
\fP
.fi
.RE
.LP
The values for all the keywords that are non-null shall be concatenated
together, each separated by a \fB'/'\fP . The default
shall be ( \fBpath\fP) if the keyword \fBpath\fP is defined; otherwise,
the default shall be ( \fBprefix\fP, \fBname\fP).
.TP 7
11.
An additional conversion specifier character, \fBL\fP , shall be used
to specify a symbolic line expansion. If the current
file is a symbolic link, then \fB%L\fP shall expand to: 
.sp
.RS
.nf

\fB"%s -> %s", <\fP\fIvalue of keyword\fP\fB>, <\fP\fIcontents of link\fP\fB>
\fP
.fi
.RE
.LP
Otherwise, the \fB%L\fP conversion specification shall be the equivalent
of \fB%F\fP .
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIdirectory\fP
The destination directory pathname for \fBcopy\fP mode.
.TP 7
\fIfile\fP
A pathname of a file to be copied or archived.
.TP 7
\fIpattern\fP
A pattern matching one or more pathnames of archive members. A pattern
must be given in the name-generating notation of the
pattern matching notation in \fIPattern Matching Notation\fP , including
the filename
expansion rules in \fIPatterns Used for Filename Expansion\fP . The
default, if no
\fIpattern\fP is specified, is to select all members in the archive.
.sp
.SH STDIN
.LP
In \fBwrite\fP mode, the standard input shall be used only if no \fIfile\fP
operands are specified. It shall be a text file
containing a list of pathnames, one per line, without leading or trailing
<blank>s.
.LP
In \fBlist\fP and \fBread\fP modes, if \fB-f\fP is not specified,
the standard input shall be an archive file.
.LP
Otherwise, the standard input shall not be used.
.SH INPUT FILES
.LP
The input file named by the \fIarchive\fP option-argument, or standard
input when the archive is read from there, shall be a
file formatted according to one of the specifications in the EXTENDED
DESCRIPTION section or some other implementation-defined
format.
.LP
The file \fB/dev/tty\fP shall be used to write prompts and read responses.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIpax\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_COLLATE\fP
.sp
Determine the locale for the behavior of ranges, equivalence classes,
and multi-character collating elements used in the pattern
matching expressions for the \fIpattern\fP operand, the basic regular
expression for the \fB-s\fP option, and the extended
regular expression defined for the \fByesexpr\fP locale keyword in
the \fILC_MESSAGES\fP category.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files), the
behavior of character classes used in the extended regular
expression defined for the \fByesexpr\fP locale keyword in the \fILC_MESSAGES\fP
category, and pattern matching.
.TP 7
\fILC_MESSAGES\fP
Determine the locale for the processing of affirmative responses that
should be used to affect the format and contents of
diagnostic messages written to standard error.
.TP 7
\fILC_TIME\fP
Determine the format and contents of date and time strings when the
\fB-v\fP option is specified.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fITMPDIR\fP
Determine the pathname that provides part of the default global extended
header record file, as described for the \fB-o\fP
\fBglobexthdr=\fP keyword in the OPTIONS section.
.TP 7
\fITZ\fP
Determine the timezone used to calculate date and time strings when
the \fB-v\fP option is specified. If \fITZ\fP is unset or
null, an unspecified default timezone shall be used.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
In \fBwrite\fP mode, if \fB-f\fP is not specified, the standard output
shall be the archive formatted according to one of the
specifications in the EXTENDED DESCRIPTION section, or some other
implementation-defined format (see \fB-x\fP \fIformat\fP).
.LP
In \fBlist\fP mode, when the \fB-o\fP \fBlistopt\fP= \fIformat\fP
has been specified, the selected archive members shall be
written to standard output using the format described under List Mode
Format Specifications . In
\fBlist\fP mode without the \fB-o\fP \fBlistopt\fP= \fIformat\fP option,
the table of contents of the selected archive members
shall be written to standard output using the following format:
.sp
.RS
.nf

\fB"%s\\n", <\fP\fIpathname\fP\fB>
\fP
.fi
.RE
.LP
If the \fB-v\fP option is specified in \fBlist\fP mode, the table
of contents of the selected archive members shall be written
to standard output using the following formats.
.LP
For pathnames representing hard links to previous members of the archive:
.sp
.RS
.nf

\fB"%s == %s\\n", <\fP\fIls\fP \fB-l\fP \fIlisting\fP\fB>, <\fP\fIlinkname\fP\fB>
\fP
.fi
.RE
.LP
For all other pathnames:
.sp
.RS
.nf

\fB"%s\\n", <\fP\fIls\fP \fB-l\fP \fIlisting\fP\fB>
\fP
.fi
.RE
.LP
where <\fIls\ \fP -l\ \fIlisting\fP> shall be the format specified
by the \fIls\fP utility with the \fB-l\fP option. When writing pathnames
in this format, it is unspecified
what is written for fields for which the underlying archive format
does not have the correct information, although the correct
number of <blank>-separated fields shall be written.
.LP
In \fBlist\fP mode, standard output shall not be buffered more than
a line at a time.
.SH STDERR
.LP
If \fB-v\fP is specified in \fBread\fP, \fBwrite\fP, or \fBcopy\fP
modes, \fIpax\fP shall write the pathnames it processes
to the standard error output using the following format:
.sp
.RS
.nf

\fB"%s\\n", <\fP\fIpathname\fP\fB>
\fP
.fi
.RE
.LP
These pathnames shall be written as soon as processing is begun on
the file or archive member, and shall be flushed to standard
error. The trailing <newline>, which shall not be buffered, is written
when the file has been read or written.
.LP
If the \fB-s\fP option is specified, and the replacement string has
a trailing \fB'p'\fP , substitutions shall be written to
standard error in the following format:
.sp
.RS
.nf

\fB"%s >> %s\\n", <\fP\fIoriginal pathname\fP\fB>, <\fP\fInew pathname\fP\fB>
\fP
.fi
.RE
.LP
In all operating modes of \fIpax\fP, optional messages of unspecified
format concerning the input archive format and volume
number, the number of files, blocks, volumes, and media parts as well
as other diagnostic messages may be written to standard
error.
.LP
In all formats, for both standard output and standard error, it is
unspecified how non-printable characters in pathnames or link
names are written.
.LP
When \fIpax\fP is in \fBread\fP mode or \fBlist\fP mode, using the
\fB-x\fP \fBpax\fP archive format, and a filename, link
name, owner name, or any other field in an extended header record
cannot be translated from the \fBpax\fP UTF-8 codeset format to
the codeset and current locale of the implementation, \fIpax\fP shall
write a diagnostic message to standard error, shall process
the file as described for the \fB-o\fP \fBinvalid=\fP option, and
then shall process the next file in the archive.
.SH OUTPUT FILES
.LP
In \fBread\fP mode, the extracted output files shall be of the archived
file type. In \fBcopy\fP mode, the copied output files
shall be the type of the file being copied. In either mode, existing
files in the destination hierarchy shall be overwritten only
when all permission ( \fB-p\fP), modification time ( \fB-u\fP), and
invalid-value ( \fB-o\fP \fBinvalid\fP=) tests allow
it.
.LP
In \fBwrite\fP mode, the output file named by the \fB-f\fP option-argument
shall be a file formatted according to one of the
specifications in the EXTENDED DESCRIPTION section, or some other
implementation-defined format.
.SH EXTENDED DESCRIPTION
.SS pax Interchange Format
.LP
A \fIpax\fP archive tape or file produced in the \fB-x\fP \fBpax\fP
format shall contain a series of blocks. The physical
layout of the archive shall be identical to the \fBustar\fP format
described in ustar Interchange
Format . Each file archived shall be represented by the following
sequence:
.IP " *" 3
An optional header block with extended header records. This header
block is of the form described in pax Header Block , with a \fItypeflag\fP
value of \fBx\fP or \fBg\fP. The extended header records,
described in pax Extended Header , shall be included as the data for
this header block.
.LP
.IP " *" 3
A header block that describes the file. Any fields in the preceding
optional extended header shall override the associated
fields in this header block for this file.
.LP
.IP " *" 3
Zero or more blocks that contain the contents of the file.
.LP
.LP
At the end of the archive file there shall be two 512-byte blocks
filled with binary zeros, interpreted as an end-of-archive
indicator.
.LP
A schematic of an example archive with global extended header records
and two actual files is shown in pax
Format Archive Example . In the example, the second file in the archive
has no extended header preceding it, presumably because
it has no need for extended attributes.
.TP 7
.sp
.sp
.ce 1
\fBFigure: pax Format Archive Example\fP
.SS pax Header Block
.LP
The \fBpax\fP header block shall be identical to the \fBustar\fP header
block described in ustar
Interchange Format , except that two additional \fItypeflag\fP values
are defined:
.TP 7
\fBx\fP
Represents extended header records for the following file in the archive
(which shall have its own \fBustar\fP header block).
The format of these extended header records shall be as described
in pax Extended Header .
.TP 7
\fBg\fP
Represents global extended header records for the following files
in the archive. The format of these extended header records
shall be as described in pax Extended Header . Each value shall affect
all subsequent files that do
not override that value in their own extended header record and until
another global extended header record is reached that
provides another value for the same field. The \fItypeflag\fP \fBg\fP
global headers should not be used with interchange media
that could suffer partial data loss in transporting the archive.
.sp
.LP
For both of these types, the \fIsize\fP field shall be the size of
the extended header records in octets. The other fields in
the header block are not meaningful to this version of the \fIpax\fP
utility. However, if this archive is read by a \fIpax\fP
utility conforming to the ISO\ POSIX-2:1993 standard, the header block
fields are used to create a regular file that contains
the extended header records as data. Therefore, header block field
values should be selected to provide reasonable file access to
this regular file.
.LP
A further difference from the \fBustar\fP header block is that data
blocks for files of \fItypeflag\fP 1 (the digit one) (hard
link) may be included, which means that the size field may be greater
than zero. Archives created by \fIpax\fP \fB-o\fP
\fBlinkdata\fP shall include these data blocks with the hard links.
.SS pax Extended Header
.LP
A \fBpax\fP extended header contains values that are inappropriate
for the \fBustar\fP header block because of limitations in
that format: fields requiring a character encoding other than that
described in the ISO/IEC\ 646:1991 standard, fields
representing file attributes not described in the \fBustar\fP header,
and fields whose format or length do not fit the
requirements of the \fBustar\fP header. The values in an extended
header add attributes to the following file (or files; see the
description of the \fItypeflag\fP \fBg\fP header block) or override
values in the following header block(s), as indicated in the
following list of keywords.
.LP
An extended header shall consist of one or more records, each constructed
as follows:
.sp
.RS
.nf

\fB"%d %s=%s\\n", <\fP\fIlength\fP\fB>, <\fP\fIkeyword\fP\fB>, <\fP\fIvalue\fP\fB>
\fP
.fi
.RE
.LP
The extended header records shall be encoded according to the ISO/IEC\ 10646-1:2000
standard (UTF-8). The
<\fIlength\fP> field, <blank>, equals sign, and <newline> shown shall
be limited to the portable character set,
as encoded in UTF-8. The <\fIkeyword\fP> and <\fIvalue\fP> fields
can be any UTF-8 characters. The
<\fIlength\fP> field shall be the decimal length of the extended header
record in octets, including the trailing
<newline>.
.LP
The <\fIkeyword\fP> field shall be one of the entries from the following
list or a keyword provided as an implementation
extension. Keywords consisting entirely of lowercase letters, digits,
and periods are reserved for future standardization. A
keyword shall not include an equals sign. (In the following list,
the notations "file(s)" or "block(s)" is used to acknowledge
that a keyword affects the following single file after a \fItypeflag\fP
\fBx\fP extended header, but possibly multiple files
after \fItypeflag\fP \fBg\fP. Any requirements in the list for \fIpax\fP
to include a record when in \fBwrite\fP or \fBcopy\fP
mode shall apply only when such a record has not already been provided
through the use of the \fB-o\fP option. When used in
\fBcopy\fP mode, \fIpax\fP shall behave as if an archive had been
created with applicable extended header records and then
extracted.)
.TP 7
\fBatime\fP
The file access time for the following file(s), equivalent to the
value of the \fIst_atime\fP member of the \fBstat\fP
structure for a file, as described by the \fIstat\fP() function. The
access time shall be
restored if the process has the appropriate privilege required to
do so. The format of the <\fIvalue\fP> shall be as
described in pax Extended Header File Times .
.TP 7
\fBcharset\fP
The name of the character set used to encode the data in the following
file(s). The entries in the following table are defined
to refer to known standards; additional names may be agreed on between
the originator and recipient. 
.TS C
center; l2 l.
\fB<value>\fP	\fBFormal Standard\fP
ISO-IR 646 1990	ISO/IEC 646:1990
ISO-IR 8859 1 1998	ISO/IEC 8859-1:1998
ISO-IR 8859 2 1999	ISO/IEC 8859-2:1999
ISO-IR 8859 3 1999	ISO/IEC 8859-3:1999
ISO-IR 8859 4 1998	ISO/IEC 8859-4:1998
ISO-IR 8859 5 1999	ISO/IEC 8859-5:1999
ISO-IR 8859 6 1999	ISO/IEC 8859-6:1999
ISO-IR 8859 7 1987	ISO/IEC 8859-7:1987
ISO-IR 8859 8 1999	ISO/IEC 8859-8:1999
ISO-IR 8859 9 1999	ISO/IEC 8859-9:1999
ISO-IR 8859 10 1998	ISO/IEC 8859-10:1998
ISO-IR 8859 13 1998	ISO/IEC 8859-13:1998
ISO-IR 8859 14 1998	ISO/IEC 8859-14:1998
ISO-IR 8859 15 1999	ISO/IEC 8859-15:1999
ISO-IR 10646 2000	ISO/IEC 10646:2000
ISO-IR 10646 2000 UTF-8	ISO/IEC 10646, UTF-8 encoding
BINARY	None.
.TE
.LP
The encoding is included in an extended header for information only;
when \fIpax\fP is used as described in
IEEE\ Std\ 1003.1-2001, it shall not translate the file data into
any other encoding. The \fBBINARY\fP entry indicates
unencoded binary data.
.LP
When used in \fBwrite\fP or \fBcopy\fP mode, it is implementation-defined
whether \fIpax\fP includes a \fBcharset\fP
extended header record for a file.
.TP 7
\fBcomment\fP
A series of characters used as a comment. All characters in the <\fIvalue\fP>
field shall be ignored by \fIpax\fP.
.TP 7
\fBctime\fP
The file creation time for the following file(s), equivalent to the
value of the \fIst_ctime\fP member of the \fBstat\fP
structure for a file, as described by the \fIstat\fP() function. The
creation time shall be
restored if the process has the appropriate privilege required to
do so. The format of the <\fIvalue\fP> shall be as
described in pax Extended Header File Times .
.TP 7
\fBgid\fP
The group ID of the group that owns the file, expressed as a decimal
number using digits from the ISO/IEC\ 646:1991
standard. This record shall override the \fIgid\fP field in the following
header block(s). When used in \fBwrite\fP or
\fBcopy\fP mode, \fIpax\fP shall include a \fIgid\fP extended header
record for each file whose group ID is greater than 2097151
(octal 7777777).
.TP 7
\fBgname\fP
The group of the file(s), formatted as a group name in the group database.
This record shall override the \fIgid\fP and
\fIgname\fP fields in the following header block(s), and any \fIgid\fP
extended header record. When used in \fBread\fP,
\fBcopy\fP, or \fBlist\fP mode, \fIpax\fP shall translate the name
from the UTF-8 encoding in the header record to the character
set appropriate for the group database on the receiving system. If
any of the UTF-8 characters cannot be translated, and if the
\fB-o\fP \fBinvalid=\fP UTF-8 option is not specified, the results
are implementation-defined. When used in \fBwrite\fP or
\fBcopy\fP mode, \fIpax\fP shall include a \fBgname\fP extended header
record for each file whose group name cannot be
represented entirely with the letters and digits of the portable character
set.
.TP 7
\fBlinkpath\fP
The pathname of a link being created to another file, of any type,
previously archived. This record shall override the
\fIlinkname\fP field in the following \fBustar\fP header block(s).
The following \fBustar\fP header block shall determine the
type of link created. If \fItypeflag\fP of the following header block
is 1, it shall be a hard link. If \fItypeflag\fP is 2, it
shall be a symbolic link and the \fBlinkpath\fP value shall be the
contents of the symbolic link. The \fIpax\fP utility shall
translate the name of the link (contents of the symbolic link) from
the UTF-8 encoding to the character set appropriate for the
local file system. When used in \fBwrite\fP or \fBcopy\fP mode, \fIpax\fP
shall include a \fBlinkpath\fP extended header record
for each link whose pathname cannot be represented entirely with the
members of the portable character set other than NUL.
.TP 7
\fBmtime\fP
The file modification time of the following file(s), equivalent to
the value of the \fIst_mtime\fP member of the \fBstat\fP
structure for a file, as described in the \fIstat\fP() function. This
record shall override
the \fImtime\fP field in the following header block(s). The modification
time shall be restored if the process has the appropriate
privilege required to do so. The format of the <\fIvalue\fP> shall
be as described in pax
Extended Header File Times .
.TP 7
\fBpath\fP
The pathname of the following file(s). This record shall override
the \fIname\fP and \fIprefix\fP fields in the following
header block(s). The \fIpax\fP utility shall translate the pathname
of the file from the UTF-8 encoding to the character set
appropriate for the local file system. 
.LP
When used in \fBwrite\fP or \fBcopy\fP mode, \fIpax\fP shall include
a \fIpath\fP extended header record for each file whose
pathname cannot be represented entirely with the members of the portable
character set other than NUL.
.TP 7
\fBrealtime.\fP\fIany\fP
The keywords prefixed by "realtime." are reserved for future standardization.
.TP 7
\fBsecurity.\fP\fIany\fP
The keywords prefixed by "security." are reserved for future standardization.
.TP 7
\fBsize\fP
The size of the file in octets, expressed as a decimal number using
digits from the ISO/IEC\ 646:1991 standard. This record
shall override the \fIsize\fP field in the following header block(s).
When used in \fBwrite\fP or \fBcopy\fP mode, \fIpax\fP
shall include a \fIsize\fP extended header record for each file with
a size value greater than 8589934591 (octal
77777777777).
.TP 7
\fBuid\fP
The user ID of the file owner, expressed as a decimal number using
digits from the ISO/IEC\ 646:1991 standard. This record
shall override the \fIuid\fP field in the following header block(s).
When used in \fBwrite\fP or \fBcopy\fP mode, \fIpax\fP
shall include a \fIuid\fP extended header record for each file whose
owner ID is greater than 2097151 (octal 7777777).
.TP 7
\fBuname\fP
The owner of the following file(s), formatted as a user name in the
user database. This record shall override the \fIuid\fP
and \fIuname\fP fields in the following header block(s), and any \fIuid\fP
extended header record. When used in \fBread\fP,
\fBcopy\fP, or \fBlist\fP mode, \fIpax\fP shall translate the name
from the UTF-8 encoding in the header record to the character
set appropriate for the user database on the receiving system. If
any of the UTF-8 characters cannot be translated, and if the
\fB-o\fP \fBinvalid=\fP UTF-8 option is not specified, the results
are implementation-defined. When used in \fBwrite\fP or
\fBcopy\fP mode, \fIpax\fP shall include a \fBuname\fP extended header
record for each file whose user name cannot be
represented entirely with the letters and digits of the portable character
set.
.sp
.LP
If the <\fIvalue\fP> field is zero length, it shall delete any header
block field, previously entered extended header
value, or global extended header value of the same name.
.LP
If a keyword in an extended header record (or in a \fB-o\fP option-argument)
overrides or deletes a corresponding field in the
\fBustar\fP header block, \fIpax\fP shall ignore the contents of that
header block field.
.LP
Unlike the \fBustar\fP header block fields, NULs shall not delimit
<\fIvalue\fP>s; all characters within the
<\fIvalue\fP> field shall be considered data for the field. None of
the length limitations of the \fBustar\fP header block
fields in ustar Header Block shall apply to the extended header records.
.SS pax Extended Header Keyword Precedence
.LP
This section describes the precedence in which the various header
records and fields and command line options are selected to
apply to a file in the archive. When \fIpax\fP is used in \fBread\fP
or \fBlist\fP modes, it shall determine a file attribute in
the following sequence:
.IP " 1." 4
If \fB-o\fP \fBdelete=\fP \fIkeyword-prefix\fP is used, the affected
attributes shall be determined from step 7., if
applicable, or ignored otherwise.
.LP
.IP " 2." 4
If \fB-o\fP \fIkeyword\fP:= is used, the affected attributes shall
be ignored.
.LP
.IP " 3." 4
If \fB-o\fP \fIkeyword\fP \fB:=\fP \fIvalue\fP is used, the affected
attribute shall be assigned the value.
.LP
.IP " 4." 4
If there is a \fItypeflag\fP \fBx\fP extended header record, the affected
attribute shall be assigned the
<\fIvalue\fP>. When extended header records conflict, the last one
given in the header shall take precedence.
.LP
.IP " 5." 4
If \fB-o\fP \fIkeyword\fP \fB=\fP \fIvalue\fP is used, the affected
attribute shall be assigned the value.
.LP
.IP " 6." 4
If there is a \fItypeflag\fP \fBg\fP global extended header record,
the affected attribute shall be assigned the
<\fIvalue\fP>. When global extended header records conflict, the last
one given in the global header shall take
precedence.
.LP
.IP " 7." 4
Otherwise, the attribute shall be determined from the \fBustar\fP
header block.
.LP
.SS pax Extended Header File Times
.LP
The \fIpax\fP utility shall write an \fBmtime\fP record for each file
in \fBwrite\fP or \fBcopy\fP modes if the file's
modification time cannot be represented exactly in the \fBustar\fP
header logical record described in ustar Interchange Format . This
can occur if the time is out of \fBustar\fP range, or if the file
system
of the underlying implementation supports non-integer time granularities
and the time is not an integer. All of these time records
shall be formatted as a decimal representation of the time in seconds
since the Epoch. If a period ( \fB'.'\fP ) decimal point
character is present, the digits to the right of the point shall represent
the units of a subsecond timing granularity, where the
first digit is tenths of a second and each subsequent digit is a tenth
of the previous digit. In \fBread\fP or \fBcopy\fP mode,
the \fIpax\fP utility shall truncate the time of a file to the greatest
value that is not greater than the input header file time.
In \fBwrite\fP or \fBcopy\fP mode, the \fIpax\fP utility shall output
a time exactly if it can be represented exactly as a
decimal number, and otherwise shall generate only enough digits so
that the same time shall be recovered if the file is extracted
on a system whose underlying implementation supports the same time
granularity.
.SS ustar Interchange Format
.LP
A \fBustar\fP archive tape or file shall contain a series of logical
records. Each logical record shall be a fixed-size logical
record of 512 octets (see below). Although this format may be thought
of as being stored on 9-track industry-standard 12.7 mm (0.5
in) magnetic tape, other types of transportable media are not excluded.
Each file archived shall be represented by a header logical
record that describes the file, followed by zero or more logical records
that give the contents of the file. At the end of the
archive file there shall be two 512-octet logical records filled with
binary zeros, interpreted as an end-of-archive indicator.
.LP
The logical records may be grouped for physical I/O operations, as
described under the \fB-b\fP \fIblocksize\fP and \fB-x\fP
\fBustar\fP options. Each group of logical records may be written
with a single operation equivalent to the \fIwrite\fP() function.
On magnetic tape, the result of this write shall be a single tape
physical
block. The last physical block shall always be the full size, so logical
records after the two zero logical records may contain
undefined data.
.LP
The header logical record shall be structured as shown in the following
table. All lengths and offsets are in decimal.
.br
.sp
.ce 1
\fBTable: ustar Header Block\fP
.TS C
center; l l l.
\fBField Name\fP	\fBOctet Offset\fP	\fBLength (in Octets)\fP
\fIname\fP	0	100
\fImode\fP	100	8
\fIuid\fP	108	8
\fIgid\fP	116	8
\fIsize\fP	124	12
\fImtime\fP	136	12
\fIchksum\fP	148	8
\fItypeflag\fP	156	1
\fIlinkname\fP	157	100
\fImagic\fP	257	6
\fIversion\fP	263	2
\fIuname\fP	265	32
\fIgname\fP	297	32
\fIdevmajor\fP	329	8
\fIdevminor\fP	337	8
\fIprefix\fP	345	155
.TE
.LP
All characters in the header logical record shall be represented in
the coded character set of the ISO/IEC\ 646:1991
standard. For maximum portability between implementations, names should
be selected from characters represented by the portable
filename character set as octets with the most significant bit zero.
If an implementation supports the use of characters outside of
slash and the portable filename character set in names for files,
users, and groups, one or more implementation-defined encodings
of these characters shall be provided for interchange purposes.
.LP
However, the \fIpax\fP utility shall never create filenames on the
local system that cannot be accessed via the procedures
described in IEEE\ Std\ 1003.1-2001. If a filename is found on the
medium that would create an invalid filename, it is
implementation-defined whether the data from the file is stored on
the file hierarchy and under what name it is stored. The
\fIpax\fP utility may choose to ignore these files as long as it produces
an error indicating that the file is being ignored.
.LP
Each field within the header logical record is contiguous; that is,
there is no padding used. Each character on the archive
medium shall be stored contiguously.
.LP
The fields \fImagic\fP, \fIuname\fP, and \fIgname\fP are character
strings each terminated by a NUL character. The fields
\fIname\fP, \fIlinkname\fP, and \fIprefix\fP are NUL-terminated character
strings except when all characters in the array
contain non-NUL characters including the last character. The \fIversion\fP
field is two octets containing the characters
\fB"00"\fP (zero-zero). The \fItypeflag\fP contains a single character.
All other fields are leading zero-filled octal numbers
using digits from the ISO/IEC\ 646:1991 standard IRV. Each numeric
field is terminated by one or more <space> or NUL
characters.
.LP
The \fIname\fP and the \fIprefix\fP fields shall produce the pathname
of the file. A new pathname shall be formed, if
\fIprefix\fP is not an empty string (its first character is not NUL),
by concatenating \fIprefix\fP (up to the first NUL
character), a slash character, and \fIname\fP; otherwise, \fIname\fP
is used alone. In either case, \fIname\fP is terminated at
the first NUL character. If \fIprefix\fP begins with a NUL character,
it shall be ignored. In this manner, pathnames of at most
256 characters can be supported. If a pathname does not fit in the
space provided, \fIpax\fP shall notify the user of the error,
and shall not store any part of the file-header or data-on the medium.
.LP
The \fIlinkname\fP field, described below, shall not use the \fIprefix\fP
to produce a pathname. As such, a \fIlinkname\fP is
limited to 100 characters. If the name does not fit in the space provided,
\fIpax\fP shall notify the user of the error, and shall
not attempt to store the link on the medium.
.LP
The \fImode\fP field provides 12 bits encoded in the ISO/IEC\ 646:1991
standard octal digit representation. The encoded
bits shall represent the following values:
.br
.sp
.ce 1
\fBTable: ustar \fImode\fP Field\fP
.TS C
center; l1 l1 lw(37).
\fBBit Value\fP	\fBIEEE\ Std\ 1003.1-2001 Bit\fP	T{
.na
\fBDescription\fP
.ad
T}
04000	S_ISUID	T{
.na
Set UID on execution.
.ad
T}
02000	S_ISGID	T{
.na
Set GID on execution.
.ad
T}
01000	<reserved>	T{
.na
Reserved for future standardization.
.ad
T}
00400	S_IRUSR	T{
.na
Read permission for file owner class.
.ad
T}
00200	S_IWUSR	T{
.na
Write permission for file owner class.
.ad
T}
00100	S_IXUSR	T{
.na
Execute/search permission for file owner class.
.ad
T}
00040	S_IRGRP	T{
.na
Read permission for file group class.
.ad
T}
00020	S_IWGRP	T{
.na
Write permission for file group class.
.ad
T}
00010	S_IXGRP	T{
.na
Execute/search permission for file group class.
.ad
T}
00004	S_IROTH	T{
.na
Read permission for file other class.
.ad
T}
00002	S_IWOTH	T{
.na
Write permission for file other class.
.ad
T}
00001	S_IXOTH	T{
.na
Execute/search permission for file other class.
.ad
T}
.TE
.LP
When appropriate privilege is required to set one of these mode bits,
and the user restoring the files from the archive does not
have the appropriate privilege, the mode bits for which the user does
not have appropriate privilege shall be ignored. Some of the
mode bits in the archive format are not mentioned elsewhere in this
volume of IEEE\ Std\ 1003.1-2001. If the implementation
does not support those bits, they may be ignored.
.LP
The \fIuid\fP and \fIgid\fP fields are the user and group ID of the
owner and group of the file, respectively.
.LP
The \fIsize\fP field is the size of the file in octets. If the \fItypeflag\fP
field is set to specify a file to be of type 1
(a link) or 2 (a symbolic link), the \fIsize\fP field shall be specified
as zero. If the \fItypeflag\fP field is set to specify a
file of type 5 (directory), the \fIsize\fP field shall be interpreted
as described under the definition of that record type. No
data logical records are stored for types 1, 2, or 5. If the \fItypeflag\fP
field is set to 3 (character special file), 4 (block
special file), or 6 (FIFO), the meaning of the \fIsize\fP field is
unspecified by this volume of IEEE\ Std\ 1003.1-2001,
and no data logical records shall be stored on the medium. Additionally,
for type 6, the \fIsize\fP field shall be ignored when
reading. If the \fItypeflag\fP field is set to any other value, the
number of logical records written following the header shall
be ( \fIsize\fP+511)/512, ignoring any fraction in the result of the
division.
.LP
The \fImtime\fP field shall be the modification time of the file at
the time it was archived. It is the ISO/IEC\ 646:1991
standard representation of the octal value of the modification time
obtained from the \fIstat\fP() function.
.LP
The \fIchksum\fP field shall be the ISO/IEC\ 646:1991 standard IRV
representation of the octal value of the simple sum of
all octets in the header logical record. Each octet in the header
shall be treated as an unsigned value. These values shall be
added to an unsigned integer, initialized to zero, the precision of
which is not less than 17 bits. When calculating the checksum,
the \fIchksum\fP field is treated as if it were all spaces.
.LP
The \fItypeflag\fP field specifies the type of file archived. If a
particular implementation does not recognize the type, or
the user does not have appropriate privilege to create that type,
the file shall be extracted as if it were a regular file if the
file type is defined to have a meaning for the \fIsize\fP field that
could cause data logical records to be written on the medium
(see the previous description for \fIsize\fP). If conversion to a
regular file occurs, the \fIpax\fP utility shall produce an
error indicating that the conversion took place. All of the \fItypeflag\fP
fields shall be coded in the ISO/IEC\ 646:1991
standard IRV:
.TP 7
\fB0\fP
Represents a regular file. For backwards-compatibility, a \fItypeflag\fP
value of binary zero ( \fB'\\0'\fP ) should be
recognized as meaning a regular file when extracting files from the
archive. Archives written with this version of the archive file
format create regular files with a \fItypeflag\fP value of the ISO/IEC\ 646:1991
standard IRV \fB'0'\fP .
.TP 7
\fB1\fP
Represents a file linked to another file, of any type, previously
archived. Such files are identified by each file having the
same device and file serial number. The linked-to name is specified
in the \fIlinkname\fP field with a NUL-character terminator if
it is less than 100 octets in length.
.TP 7
\fB2\fP
Represents a symbolic link. The contents of the symbolic link shall
be stored in the \fIlinkname\fP field.
.TP 7
\fB3,4\fP
Represent character special files and block special files respectively.
In this case the \fIdevmajor\fP and \fIdevminor\fP
fields shall contain information defining the device, the format of
which is unspecified by this volume of
IEEE\ Std\ 1003.1-2001. Implementations may map the device specifications
to their own local specification or may ignore
the entry.
.TP 7
\fB5\fP
Specifies a directory or subdirectory. On systems where disk allocation
is performed on a directory basis, the \fIsize\fP
field shall contain the maximum number of octets (which may be rounded
to the nearest disk block allocation unit) that the
directory may hold. A \fIsize\fP field of zero indicates no such limiting.
Systems that do not support limiting in this manner
should ignore the \fIsize\fP field.
.TP 7
\fB6\fP
Specifies a FIFO special file. Note that the archiving of a FIFO file
archives the existence of this file and not its
contents.
.TP 7
\fB7\fP
Reserved to represent a file to which an implementation has associated
some high-performance attribute. Implementations without
such extensions should treat this file as a regular file (type 0).
.TP 7
\fBA-Z\fP
The letters \fB'A'\fP to \fB'Z'\fP , inclusive, are reserved for custom
implementations. All other values are reserved
for future versions of IEEE\ Std\ 1003.1-2001.
.sp
.LP
Attempts to archive a socket using \fBustar\fP interchange format
shall produce a diagnostic message. Handling of other file
types is implementation-defined.
.LP
The \fImagic\fP field is the specification that this archive was output
in this archive format. If this field contains
\fBustar\fP (the five characters from the ISO/IEC\ 646:1991 standard
IRV shown followed by NUL), the \fIuname\fP and
\fIgname\fP fields shall contain the ISO/IEC\ 646:1991 standard IRV
representation of the owner and group of the file,
respectively (truncated to fit, if necessary). When the file is restored
by a privileged, protection-preserving version of the
utility, the user and group databases shall be scanned for these names.
If found, the user and group IDs contained within these
files shall be used rather than the values contained within the \fIuid\fP
and \fIgid\fP fields.
.SS cpio Interchange Format
.LP
The octet-oriented \fBcpio\fP archive format shall be a series of
entries, each comprising a header that describes the file,
the name of the file, and then the contents of the file.
.LP
An archive may be recorded as a series of fixed-size blocks of octets.
This blocking shall be used only to make physical I/O
more efficient. The last group of blocks shall always be at the full
size.
.LP
For the octet-oriented \fBcpio\fP archive format, the individual entry
information shall be in the order indicated and
described by the following table; see also the \fI<cpio.h>\fP header.
.br
.sp
.ce 1
\fBTable: Octet-Oriented cpio Archive Entry\fP
.TS C
center; l2 l2 l.
\fBHeader Field Name\fP	\fBLength (in Octets)\fP	\fBInterpreted as\fP
\fIc_magic\fP	6	Octal number
\fIc_dev\fP	6	Octal number
\fIc_ino\fP	6	Octal number
\fIc_mode\fP	6	Octal number
\fIc_uid\fP	6	Octal number
\fIc_gid\fP	6	Octal number
\fIc_nlink\fP	6	Octal number
\fIc_rdev\fP	6	Octal number
\fIc_mtime\fP	11	Octal number
\fIc_namesize\fP	6	Octal number
\fIc_filesize\fP	11	Octal number
\fBFilename Field Name\fP	\fBLength\fP	\fBInterpreted as\fP
\fIc_name\fP	\fIc_namesize\fP	Pathname string
\fBFile Data Field Name\fP	\fBLength\fP	\fBInterpreted as\fP
\fIc_filedata\fP	\fIc_filesize\fP	Data
.TE
.SS cpio Header
.LP
For each file in the archive, a header as defined previously shall
be written. The information in the header fields is written
as streams of the ISO/IEC\ 646:1991 standard characters interpreted
as octal numbers. The octal numbers shall be extended to
the necessary length by appending the ISO/IEC\ 646:1991 standard IRV
zeros at the most-significant-digit end of the number; the
result is written to the most-significant digit of the stream of octets
first. The fields shall be interpreted as follows:
.TP 7
\fIc_magic\fP
Identify the archive as being a transportable archive by containing
the identifying value \fB"070707"\fP .
.TP 7
\fIc_dev\fP,\ \fIc_ino\fP
Contains values that uniquely identify the file within the archive
(that is, no files contain the same pair of \fIc_dev\fP and
\fIc_ino\fP values unless they are links to the same file). The values
shall be determined in an unspecified manner.
.TP 7
\fIc_mode\fP
Contains the file type and access permissions as defined in the following
table.
.br
.sp
.ce 1
\fBTable: Values for cpio c_mode Field\fP
.TS C
center; l2 l2 l.
\fBFile Permissions Name\fP	\fBValue\fP	\fBIndicates\fP
C_IRUSR	000400	Read by owner
C_IWUSR	000200	Write by owner
C_IXUSR	000100	Execute by owner
C_IRGRP	000040	Read by group
C_IWGRP	000020	Write by group
C_IXGRP	000010	Execute by group
C_IROTH	000004	Read by others
C_IWOTH	000002	Write by others
C_IXOTH	000001	Execute by others
C_ISUID	004000	Set \fIuid\fP
C_ISGID	002000	Set \fIgid\fP
C_ISVTX	001000	Reserved
\fBFile Type Name\fP	\fBValue\fP	\fBIndicates\fP
C_ISDIR	040000	Directory
C_ISFIFO	010000	FIFO
C_ISREG	0100000	Regular file
C_ISLNK	0120000	Symbolic link
C_ISBLK	060000	Block special file
C_ISCHR	020000	Character special file
C_ISSOCK	0140000	Socket
C_ISCTG	0110000	Reserved
.TE
.LP
Directories, FIFOs, symbolic links, and regular files shall be supported
on a system conforming to this volume of
IEEE\ Std\ 1003.1-2001; additional values defined previously are reserved
for compatibility with existing systems.
Additional file types may be supported; however, such files should
not be written to archives intended to be transported to other
systems.
.TP 7
\fIc_uid\fP
Contains the user ID of the owner.
.TP 7
\fIc_gid\fP
Contains the group ID of the group.
.TP 7
\fIc_nlink\fP
Contains the number of links referencing the file at the time the
archive was created.
.TP 7
\fIc_rdev\fP
Contains implementation-defined information for character or block
special files.
.TP 7
\fIc_mtime\fP
Contains the latest time of modification of the file at the time the
archive was created.
.TP 7
\fIc_namesize\fP
Contains the length of the pathname, including the terminating NUL
character.
.TP 7
\fIc_filesize\fP
Contains the length of the file in octets. This shall be the length
of the data section following the header structure.
.sp
.SS cpio Filename
.LP
The \fIc_name\fP field shall contain the pathname of the file. The
length of this field in octets is the value of
\fIc_namesize\fP.
.LP
If a filename is found on the medium that would create an invalid
pathname, it is implementation-defined whether the data from
the file is stored on the file hierarchy and under what name it is
stored.
.LP
All characters shall be represented in the ISO/IEC\ 646:1991 standard
IRV. For maximum portability between implementations,
names should be selected from characters represented by the portable
filename character set as octets with the most significant bit
zero. If an implementation supports the use of characters outside
the portable filename character set in names for files, users,
and groups, one or more implementation-defined encodings of these
characters shall be provided for interchange purposes. However,
the \fIpax\fP utility shall never create filenames on the local system
that cannot be accessed via the procedures described
previously in this volume of IEEE\ Std\ 1003.1-2001. If a filename
is found on the medium that would create an invalid
filename, it is implementation-defined whether the data from the file
is stored on the local file system and under what name it is
stored. The \fIpax\fP utility may choose to ignore these files as
long as it produces an error indicating that the file is being
ignored.
.SS cpio File Data
.LP
Following \fIc_name\fP, there shall be \fIc_filesize\fP octets of
data. Interpretation of such data occurs in a manner
dependent on the file. If \fIc_filesize\fP is zero, no data shall
be contained in \fIc_filedata\fP.
.LP
When restoring from an archive:
.IP " *" 3
If the user does not have the appropriate privilege to create a file
of the specified type, \fIpax\fP shall ignore the entry
and write an error message to standard error.
.LP
.IP " *" 3
Only regular files have data to be restored. Presuming a regular file
meets any selection criteria that might be imposed on the
format-reading utility by the user, such data shall be restored.
.LP
.IP " *" 3
If a user does not have appropriate privilege to set a particular
mode flag, the flag shall be ignored. Some of the mode flags
in the archive format are not mentioned elsewhere in this volume of
IEEE\ Std\ 1003.1-2001. If the implementation does not
support those flags, they may be ignored.
.LP
.SS cpio Special Entries
.LP
FIFO special files, directories, and the trailer shall be recorded
with \fIc_filesize\fP equal to zero. For other special
files, \fIc_filesize\fP is unspecified by this volume of IEEE\ Std\ 1003.1-2001.
The header for the next file entry in the
archive shall be written directly after the last octet of the file
entry preceding it. A header denoting the filename
\fBTRAILER!!!\fP shall indicate the end of the archive; the contents
of octets in the last block of the archive following such a
header are undefined.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
All files were processed successfully.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
If \fIpax\fP cannot create a file or a link when reading an archive
or cannot find a file when writing an archive, or cannot
preserve the user ID, group ID, or file mode when the \fB-p\fP option
is specified, a diagnostic message shall be written to
standard error and a non-zero exit status shall be returned, but processing
shall continue. In the case where \fIpax\fP cannot
create a link to a file, \fIpax\fP shall not, by default, create a
second copy of the file.
.LP
If the extraction of a file from an archive is prematurely terminated
by a signal or error, \fIpax\fP may have only partially
extracted the file or (if the \fB-n\fP option was not specified) may
have extracted a file of the same name as that specified by
the user, but which is not the file the user wanted. Additionally,
the file modes of extracted directories may have additional bits
from the S_IRWXU mask set as well as incorrect modification and access
times.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fB-p\fP (privileges) option was invented to reconcile differences
between historical \fItar\fP and \fIcpio\fP
implementations. In particular, the two utilities use \fB-m\fP in
diametrically opposed ways. The \fB-p\fP option also provides a
consistent means of extending the ways in which future file attributes
can be addressed, such as for enhanced security systems or
high-performance files. Although it may seem complex, there are really
two modes that are most commonly used:
.TP 7
\fB-p\ e\fP
``Preserve everything". This would be used by the historical superuser,
someone with all the appropriate privileges, to
preserve all aspects of the files as they are recorded in the archive.
The \fBe\fP flag is the sum of \fBo\fP and \fBp\fP, and
other implementation-defined attributes.
.TP 7
\fB-p\ p\fP
``Preserve" the file mode bits. This would be used by the user with
regular privileges who wished to preserve aspects of the
file other than the ownership. The file times are preserved by default,
but two other flags are offered to disable these and use
the time of extraction.
.sp
.LP
The one pathname per line format of standard input precludes pathnames
containing <newline>s. Although such pathnames
violate the portable filename guidelines, they may exist and their
presence may inhibit usage of \fIpax\fP within shell scripts.
This problem is inherited from historical archive programs. The problem
can be avoided by listing filename arguments on the command
line instead of on standard input.
.LP
It is almost certain that appropriate privileges are required for
\fIpax\fP to accomplish parts of this volume of
IEEE\ Std\ 1003.1-2001. Specifically, creating files of type block
special or character special, restoring file access
times unless the files are owned by the user (the \fB-t\fP option),
or preserving file owner, group, and mode (the \fB-p\fP
option) all probably require appropriate privileges.
.LP
In \fBread\fP mode, implementations are permitted to overwrite files
when the archive has multiple members with the same name.
This may fail if permissions on the first version of the file do not
permit it to be overwritten.
.LP
The \fBcpio\fP and \fBustar\fP formats can only support files up to
8589934592 bytes (8 * 2^30) in size.
.SH EXAMPLES
.LP
The following command:
.sp
.RS
.nf

\fBpax -w -f /dev/rmt/1m .
\fP
.fi
.RE
.LP
copies the contents of the current directory to tape drive 1, medium
density (assuming historical System V device naming
procedures-the historical BSD device name would be \fB/dev/rmt9\fP).
.LP
The following commands:
.sp
.RS
.nf

\fBmkdir\fP \fInewdir\fP\fBpax -rw\fP \fIolddir newdir\fP
.fi
.RE
.LP
copy the \fIolddir\fP directory hierarchy to \fInewdir\fP.
.sp
.RS
.nf

\fBpax -r -s ',^//*usr//*,,' -f a.pax
\fP
.fi
.RE
.LP
reads the archive \fBa.pax\fP, with all files rooted in \fB/usr\fP
in the archive extracted relative to the current
directory.
.LP
Using the option:
.sp
.RS
.nf

\fB-o listopt="%M %(atime)T %(size)D %(name)s"
\fP
.fi
.RE
.LP
overrides the default output description in Standard Output and instead
writes:
.sp
.RS
.nf

\fB-rw-rw--- Jan 12 15:53 1492 /usr/foo/bar
\fP
.fi
.RE
.LP
Using the options:
.sp
.RS
.nf

\fB-o listopt='%L\\t%(size)D\\n%.7' \\
-o listopt='(name)s\\n%(ctime)T\\n%T'
\fP
.fi
.RE
.LP
overrides the default output description in Standard Output and instead
writes:
.sp
.RS
.nf

\fB/usr/foo/bar -> /tmp   1492
/usr/fo
Jan 12 1991
Jan 31 15:53
\fP
.fi
.RE
.SH RATIONALE
.LP
The \fIpax\fP utility was new for the ISO\ POSIX-2:1993 standard.
It represents a peaceful compromise between advocates of
the historical \fItar\fP and \fIcpio\fP utilities.
.LP
A fundamental difference between \fIcpio\fP and \fItar\fP was in the
way directories were treated. The \fIcpio\fP utility did
not treat directories differently from other files, and to select
a directory and its contents required that each file in the
hierarchy be explicitly specified. For \fItar\fP, a directory matched
every file in the file hierarchy it rooted.
.LP
The \fIpax\fP utility offers both interfaces; by default, directories
map into the file hierarchy they root. The \fB-d\fP
option causes \fIpax\fP to skip any file not explicitly referenced,
as \fIcpio\fP historically did. The \fItar\fP \fB-\fP
\fIstyle\fP behavior was chosen as the default because it was believed
that this was the more common usage and because \fItar\fP
is the more commonly available interface, as it was historically provided
on both System V and BSD implementations.
.LP
The data interchange format specification in this volume of IEEE\ Std\ 1003.1-2001
requires that processes with
"appropriate privileges" shall always restore the ownership and permissions
of extracted files exactly as archived. If viewed
from the historic equivalence between superuser and "appropriate privileges",
there are two problems with this requirement.
First, users running as superusers may unknowingly set dangerous permissions
on extracted files. Second, it is needlessly limiting,
in that superusers cannot extract files and own them as superuser
unless the archive was created by the superuser. (It should be
noted that restoration of ownerships and permissions for the superuser,
by default, is historical practice in \fIcpio\fP, but not
in \fItar\fP.) In order to avoid these two problems, the \fIpax\fP
specification has an additional "privilege" mechanism, the
\fB-p\fP option. Only a \fIpax\fP invocation with the privileges needed,
and which has the \fB-p\fP option set using the
\fBe\fP specification character, has the "appropriate privilege" to
restore full ownership and permission information.
.LP
Note also that this volume of IEEE\ Std\ 1003.1-2001 requires that
the file ownership and access permissions shall be
set, on extraction, in the same fashion as the \fIcreat\fP() function
when provided with the
mode stored in the archive. This means that the file creation mask
of the user is applied to the file permissions.
.LP
Users should note that directories may be created by \fIpax\fP while
extracting files with permissions that are different from
those that existed at the time the archive was created. When extracting
sensitive information into a directory hierarchy that no
longer exists, users are encouraged to set their file creation mask
appropriately to protect these files during extraction.
.LP
The table of contents output is written to standard output to facilitate
pipeline processing.
.LP
An early proposal had hard links displaying for all pathnames. This
was removed because it complicates the output of the case
where \fB-v\fP is not specified and does not match historical \fIcpio\fP
usage. The hard-link information is available in the
\fB-v\fP display.
.LP
The description of the \fB-l\fP option allows implementations to make
hard links to symbolic links.
IEEE\ Std\ 1003.1-2001 does not specify any way to create a hard link
to a symbolic link, but many implementations provide
this capability as an extension. If there are hard links to symbolic
links when an archive is created, the implementation is
required to archive the hard link in the archive (unless \fB-H\fP
or \fB-L\fP is specified). When in \fBread\fP mode and in
\fBcopy\fP mode, implementations supporting hard links to symbolic
links should use them when appropriate.
.LP
The archive formats inherited from the POSIX.1-1990 standard have
certain restrictions that have been brought along from
historical usage. For example, there are restrictions on the length
of pathnames stored in the archive. When \fIpax\fP is used in
\fBcopy\fP( \fB-rw\fP) mode (copying directory hierarchies), the ability
to use extensions from the \fB-x\fP \fBpax\fP format
overcomes these restrictions.
.LP
The default \fIblocksize\fP value of 5120 bytes for \fIcpio\fP was
selected because it is one of the standard block-size
values for \fIcpio\fP, set when the \fB-B\fP option is specified.
(The other default block-size value for \fIcpio\fP is 512
bytes, and this was considered to be too small.) The default block
value of 10240 bytes for \fItar\fP was selected because that is
the standard block-size value for BSD \fItar\fP. The maximum block
size of 32256 bytes (2**15-512 bytes)
is the largest multiple of 512 bytes that fits into a signed 16-bit
tape controller transfer register. There are known limitations
in some historical systems that would prevent larger blocks from being
accepted. Historical values were chosen to improve
compatibility with historical scripts using \fIdd\fP or similar utilities
to manipulate
archives. Also, default block sizes for any file type other than character
special file has been deleted from this volume of
IEEE\ Std\ 1003.1-2001 as unimportant and not likely to affect the
structure of the resulting archive.
.LP
Implementations are permitted to modify the block-size value based
on the archive format or the device to which the archive is
being written. This is to provide implementations with the opportunity
to take advantage of special types of devices, and it should
not be used without a great deal of consideration as it almost certainly
decreases archive portability.
.LP
The intended use of the \fB-n\fP option was to permit extraction of
one or more files from the archive without processing the
entire archive. This was viewed by the standard developers as offering
significant performance advantages over historical
implementations. The \fB-n\fP option in early proposals had three
effects; the first was to cause special characters in patterns
to not be treated specially. The second was to cause only the first
file that matched a pattern to be extracted. The third was to
cause \fIpax\fP to write a diagnostic message to standard error when
no file was found matching a specified pattern. Only the
second behavior is retained by this volume of IEEE\ Std\ 1003.1-2001,
for many reasons. First, it is in general not
acceptable for a single option to have multiple effects. Second, the
ability to make pattern matching characters act as normal
characters is useful for parts of \fIpax\fP other than file extraction.
Third, a finer degree of control over the special
characters is useful because users may wish to normalize only a single
special character in a single filename. Fourth, given a more
general escape mechanism, the previous behavior of the \fB-n\fP option
can be easily obtained using the \fB-s\fP option or a \fIsed\fP script.
Finally, writing a diagnostic message when a pattern specified by
the user is
unmatched by any file is useful behavior in all cases.
.LP
In this version, the \fB-n\fP was removed from the \fBcopy\fP mode
synopsis of \fIpax\fP; it is inapplicable because there
are no pattern operands specified in this mode.
.LP
There is another method than \fIpax\fP for copying subtrees in IEEE\ Std\ 1003.1-2001
described as part of the \fIcp\fP utility. Both methods are historical
practice: \fIcp\fP
provides a simpler, more intuitive interface, while \fIpax\fP offers
a finer granularity of control. Each provides additional
functionality to the other; in particular, \fIpax\fP maintains the
hard-link structure of the hierarchy while \fIcp\fP does not. It is
the intention of the standard developers that the results be similar
(using
appropriate option combinations in both utilities). The results are
not required to be identical; there seemed insufficient gain to
applications to balance the difficulty of implementations having to
guarantee that the results would be exactly identical.
.LP
A single archive may span more than one file. It is suggested that
implementations provide informative messages to the user on
standard error whenever the archive file is changed.
.LP
The \fB-d\fP option (do not create intermediate directories not listed
in the archive) found in early proposals was originally
provided as a complement to the historic \fB-d\fP option of \fIcpio\fP.
It has been deleted.
.LP
The \fB-s\fP option in early proposals specified a subset of the substitution
command from the \fIed\fP utility. As there was no reason for only
a subset to be supported, the \fB-s\fP option is now
compatible with the current \fIed\fP specification. Since the delimiter
can be any non-null
character, the following usage with single spaces is valid:
.sp
.RS
.nf

\fBpax -s " foo bar " ...
\fP
.fi
.RE
.LP
The \fB-t\fP description is worded so as to note that this may cause
the access time update caused by some other activity
(which occurs while the file is being read) to be overwritten.
.LP
The default behavior of \fIpax\fP with regard to file modification
times is the same as historical implementations of
\fItar\fP. It is not the historical behavior of \fIcpio\fP.
.LP
Because the \fB-i\fP option uses \fB/dev/tty\fP, utilities without
a controlling terminal are not able to use this option.
.LP
The \fB-y\fP option, found in early proposals, has been deleted because
a line containing a single period for the \fB-i\fP
option has equivalent functionality. The special lines for the \fB-i\fP
option (a single period and the empty line) are historical
practice in \fIcpio\fP.
.LP
In early drafts, a \fB-e\fP \fIcharmap\fP option was included to increase
portability of files between systems using different
coded character sets. This option was omitted because it was apparent
that consensus could not be formed for it. In this version,
the use of UTF-8 should be an adequate substitute.
.LP
The \fB-k\fP option was added to address international concerns about
the dangers involved in the character set transformations
of \fB-e\fP (if the target character set were different from the source,
the filenames might be transformed into names matching
existing files) and also was made more general to protect files transferred
between file systems with different {NAME_MAX} values
(truncating a filename on a smaller system might also inadvertently
overwrite existing files). As stated, it prevents any
overwriting, even if the target file is older than the source. This
version adds more granularity of options to solve this problem
by introducing the \fB-o\fP \fBinvalid=\fP option-specifically the
UTF-8 action. (Note that an existing file that is named with a
UTF-8 encoding is still subject to overwriting in this case. The \fB-k\fP
option closes that loophole.)
.LP
Some of the file characteristics referenced in this volume of IEEE\ Std\ 1003.1-2001
might not be supported by some
archive formats. For example, neither the \fBtar\fP nor \fBcpio\fP
formats contain the file access time. For this reason, the
\fBe\fP specification character has been provided, intended to cause
all file characteristics specified in the archive to be
retained.
.LP
It is required that extracted directories, by default, have their
access and modification times and permissions set to the
values specified in the archive. This has obvious problems in that
the directories are almost certainly modified after being
extracted and that directory permissions may not permit file creation.
One possible solution is to create directories with the mode
specified in the archive, as modified by the \fIumask\fP of the user,
with sufficient
permissions to allow file creation. After all files have been extracted,
\fIpax\fP would then reset the access and modification
times and permissions as necessary.
.LP
The list-mode formatting description borrows heavily from the one
defined by the \fIprintf\fP utility. However, since there is no separate
operand list to get conversion arguments,
the format was extended to allow specifying the name of the conversion
argument as part of the conversion specification.
.LP
The \fBT\fP conversion specifier allows time fields to be displayed
in any of the date formats. Unlike the \fIls\fP utility, \fIpax\fP
does not adjust the format when the date is less than six months in
the
past. This makes parsing the output more predictable.
.LP
The \fBD\fP conversion specifier handles the ability to display the
major/minor or file size, as with \fIls\fP, by using \fB%-8(\fP\fIsize\fP\fB)D\fP.
.LP
The \fBL\fP conversion specifier handles the \fIls\fP display for
symbolic links.
.LP
Conversion specifiers were added to generate existing known types
used for \fIls\fP.
.SS pax Interchange Format
.LP
The new POSIX data interchange format was developed primarily to satisfy
international concerns that the \fBustar\fP and
\fBcpio\fP formats did not provide for file, user, and group names
encoded in characters outside a subset of the
ISO/IEC\ 646:1991 standard. The standard developers realized that
this new POSIX data interchange format should be very
extensible because there were other requirements they foresaw in the
near future:
.IP " *" 3
Support international character encodings and locale information
.LP
.IP " *" 3
Support security information (ACLs, and so on)
.LP
.IP " *" 3
Support future file types, such as realtime or contiguous files
.LP
.IP " *" 3
Include data areas for implementation use
.LP
.IP " *" 3
Support systems with words larger than 32 bits and timers with subsecond
granularity
.LP
.LP
The following were not goals for this format because these are better
handled by separate utilities or are inappropriate for a
portable format:
.IP " *" 3
Encryption
.LP
.IP " *" 3
Compression
.LP
.IP " *" 3
Data translation between locales and codesets
.LP
.IP " *" 3
\fIinode\fP storage
.LP
.LP
The format chosen to support the goals is an extension of the \fBustar\fP
format. Of the two formats previously available, only
the \fBustar\fP format was selected for extensions because:
.IP " *" 3
It was easier to extend in an upwards-compatible way. It offered version
flags and header block type fields with room for future
standardization. The \fBcpio\fP format, while possessing a more flexible
file naming methodology, could not be extended without
breaking some theoretical implementation or using a dummy filename
that could be a legitimate filename.
.LP
.IP " *" 3
Industry experience since the original " \fItar\fP wars" fought in
developing the ISO\ POSIX-1 standard has clearly been
in favor of the \fBustar\fP format, which is generally the default
output format selected for \fIpax\fP implementations on new
systems.
.LP
.LP
The new format was designed with one additional goal in mind: reasonable
behavior when an older \fItar\fP or \fIpax\fP utility
happened to read an archive. Since the POSIX.1-1990 standard mandated
that a "format-reading utility" had to treat unrecognized
\fItypeflag\fP values as regular files, this allowed the format to
include all the extended information in a pseudo-regular file
that preceded each real file. An option is given that allows the archive
creator to set up reasonable names for these files on the
older systems. Also, the normative text suggests that reasonable file
access values be used for this \fBustar\fP header block.
Making these header files inaccessible for convenient reading and
deleting would not be reasonable. File permissions of 600 or 700
are suggested.
.LP
The \fBustar\fP \fItypeflag\fP field was used to accommodate the additional
functionality of the new format rather than magic
or version because the POSIX.1-1990 standard (and, by reference, the
previous version of \fIpax\fP), mandated the behavior of the
format-reading utility when it encountered an unknown \fItypeflag\fP,
but was silent about the other two fields.
.LP
Early proposals of the first revision to IEEE\ Std\ 1003.1-2001 contained
a proposed archive format that was based on
compatibility with the standard for tape files (ISO\ 1001, similar
to the format used historically on many mainframes and
minicomputers). This format was overly complex and required considerable
overhead in volume and header records. Furthermore, the
standard developers felt that it would not be acceptable to the community
of POSIX developers, so it was later changed to be a
format more closely related to historical practice on POSIX systems.
.LP
The prefix and name split of pathnames in \fBustar\fP was replaced
by the single path extended header record for
simplicity.
.LP
The concept of a global extended header ( \fItypeflag\fP \fBg\fP)
was controversial. If this were applied to an archive being
recorded on magnetic tape, a few unreadable blocks at the beginning
of the tape could be a serious problem; a utility attempting to
extract as many files as possible from a damaged archive could lose
a large percentage of file header information in this case.
However, if the archive were on a reliable medium, such as a CD-ROM,
the global extended header offers considerable potential size
reductions by eliminating redundant information. Thus, the text warns
against using the global method for unreliable media and
provides a method for implanting global information in the extended
header for each file, rather than in the \fItypeflag\fP
\fBg\fP records.
.LP
No facility for data translation or filtering on a per-file basis
is included because the standard developers could not invent
an interface that would allow this in an efficient manner. If a filter,
such as encryption or compression, is to be applied to all
the files, it is more efficient to apply the filter to the entire
archive as a single file. The standard developers considered
interfaces that would invoke a shell script for each file going into
or out of the archive, but the system overhead in this
approach was considered to be too high.
.LP
One such approach would be to have \fBfilter=\fP records that give
a pathname for an executable. When the program is invoked,
the file and archive would be open for standard input/output and all
the header fields would be available as environment variables
or command-line arguments. The standard developers did discuss such
schemes, but they were omitted from
IEEE\ Std\ 1003.1-2001 due to concerns about excessive overhead. Also,
the program itself would need to be in the archive
if it were to be used portably.
.LP
There is currently no portable means of identifying the character
set(s) used for a file in the file system. Therefore,
\fIpax\fP has not been given a mechanism to generate charset records
automatically. The only portable means of doing this is for
the user to write the archive using the \fB-o\fP \fBcharset=\fP \fIstring\fP
command line option. This assumes that all of the
files in the archive use the same encoding. The "implementation-defined"
text is included to allow for a system that can identify
the encodings used for each of its files.
.LP
The table of standards that accompanies the charset record description
is acknowledged to be very limited. Only a limited number
of character set standards is reasonable for maximal interchange.
Any character set is, of course, possible by prior agreement. It
was suggested that EBCDIC be listed, but it was omitted because it
is not defined by a formal standard. Formal standards, and then
only those with reasonably large followings, can be included here,
simply as a matter of practicality. The <\fIvalue\fP>s
represent names of officially registered character sets in the format
required by the ISO\ 2375:1985 standard.
.LP
The normal comma or <blank>-separated list rules are not followed
in the case of keyword options to allow ease of argument
parsing for \fIgetopts\fP.
.LP
Further information on character encodings is in pax Archive Character
Set Encoding/Decoding
\&.
.LP
The standard developers have reserved keyword name space for vendor
extensions. It is suggested that the format to be used
is:
.sp
.RS
.nf

\fIVENDOR.keyword\fP
.fi
.RE
.LP
where \fIVENDOR\fP is the name of the vendor or organization in all
uppercase letters. It is further suggested that the keyword
following the period be named differently than any of the standard
keywords so that it could be used for future standardization, if
appropriate, by omitting the \fIVENDOR\fP prefix.
.LP
The <\fIlength\fP> field in the extended header record was included
to make it simpler to step through the records, even
if a record contains an unknown format (to a particular \fIpax\fP)
with complex interactions of special characters. It also
provides a minor integrity checkpoint within the records to aid a
program attempting to recover files from a damaged archive.
.LP
There are no extended header versions of the \fIdevmajor\fP and \fIdevminor\fP
fields because the unspecified format
\fBustar\fP header field should be sufficient. If they are not, vendor-specific
extended keywords (such as \fIVENDOR.devmajor\fP)
should be used.
.LP
Device and \fIi\fP-number labeling of files was not adopted from \fIcpio\fP;
files are interchanged strictly on a symbolic
name basis, as in \fBustar\fP.
.LP
Just as with the \fBustar\fP format descriptions, the new format makes
no special arrangements for multi-volume archives. Each
of the \fIpax\fP archive types is assumed to be inside a single POSIX
file and splitting that file over multiple volumes
(diskettes, tape cartridges, and so on), processing their labels,
and mounting each in the proper sequence are considered to be
implementation details that cannot be described portably.
.LP
The \fBpax\fP format is intended for interchange, not only for backup
on a single (family of) systems. It is not as densely
packed as might be possible for backup:
.IP " *" 3
It contains information as coded characters that could be coded in
binary.
.LP
.IP " *" 3
It identifies extended records with name fields that could be omitted
in favor of a fixed-field layout.
.LP
.IP " *" 3
It translates names into a portable character set and identifies locale-related
information, both of which are probably
unnecessary for backup.
.LP
.LP
The requirements on restoring from an archive are slightly different
from the historical wording, allowing for non-monolithic
privilege to bring forward as much as possible. In particular, attributes
such as "high performance file" might be broadly but
not universally granted while set-user-ID or \fIchown\fP() might be
much more restricted.
There is no implication in IEEE\ Std\ 1003.1-2001 that the security
information be honored after it is restored to the file
hierarchy, in spite of what might be improperly inferred by the silence
on that topic. That is a topic for another standard.
.LP
Links are recorded in the fashion described here because a link can
be to any file type. It is desirable in general to be able
to restore part of an archive selectively and restore all of those
files completely. If the data is not associated with each link,
it is not possible to do this. However, the data associated with a
file can be large, and when selective restoration is not needed,
this can be a significant burden. The archive is structured so that
files that have no associated data can always be restored by
the name of any link name of any link, and the user may choose whether
data is recorded with each instance of a file that contains
data. The format permits mixing of both types of links in a single
archive; this can be done for special needs, and \fIpax\fP is
expected to interpret such archives on input properly, despite the
fact that there is no \fIpax\fP option that would force this
mixed case on output. (When \fB-o\fP \fBlinkdata\fP is used, the output
must contain the duplicate data, but the implementation
is free to include it or omit it when \fB-o\fP \fBlinkdata\fP is not
used.)
.LP
The time values are included as extended header records for those
implementations needing more than the eleven octal digits
allowed by the \fBustar\fP format. Portable file timestamps cannot
be negative. If \fIpax\fP encounters a file with a negative
timestamp in \fBcopy\fP or \fBwrite\fP mode, it can reject the file,
substitute a non-negative timestamp, or generate a
non-portable timestamp with a leading \fB'-'\fP . Even though some
implementations can support finer file-time granularities
than seconds, the normative text requires support only for seconds
since the Epoch because the ISO\ POSIX-1 standard states
them that way. The \fBustar\fP format includes only \fImtime\fP; the
new format adds \fIatime\fP and \fIctime\fP for symmetry.
The \fIatime\fP access time restored to the file system will be affected
by the \fB-p\fP \fBa\fP and \fB-p\fP \fBe\fP options.
The \fIctime\fP creation time (actually \fIinode\fP modification time)
is described with "appropriate privilege" so that it can
be ignored when writing to the file system. POSIX does not provide
a portable means to change file creation time. Nothing is
intended to prevent a non-portable implementation of \fIpax\fP from
restoring the value.
.LP
The \fIgid\fP, \fIsize\fP, and \fIuid\fP extended header records were
included to allow expansion beyond the sizes specified
in the regular \fItar\fP header. New file system architectures are
emerging that will exhaust the 12-digit size field. There are
probably not many systems requiring more than 8 digits for user and
group IDs, but the extended header values were included for
completeness, allowing overrides for all of the decimal values in
the \fItar\fP header.
.LP
The standard developers intended to describe the effective results
of \fIpax\fP with regard to file ownerships and permissions;
implementations are not restricted in timing or sequencing the restoration
of such, provided the results are as specified.
.LP
Much of the text describing the extended headers refers to use in
" \fBwrite\fP or \fBcopy\fP modes". The \fBcopy\fP mode
references are due to the normative text: "The effect of the copy
shall be as if the copied files were written to an archive file
and then subsequently extracted ...". There is certainly no way to
test whether \fIpax\fP is actually generating the extended
headers in \fBcopy\fP mode, but the effects must be as if it had.
.SS pax Archive Character Set Encoding/Decoding
.LP
There is a need to exchange archives of files between systems of different
native codesets. Filenames, group names, and user
names must be preserved to the fullest extent possible when an archive
is read on the receiving platform. Translation of the
contents of files is not within the scope of the \fIpax\fP utility.
.LP
There will also be the need to represent characters that are not available
on the receiving platform. These unsupported
characters cannot be automatically folded to the local set of characters
due to the chance of collisions. This could result in
overwriting previous extracted files from the archive or pre-existing
files on the system.
.LP
For these reasons, the codeset used to represent characters within
the extended header records of the \fIpax\fP archive must be
sufficiently rich to handle all commonly used character sets. The
fields requiring translation include, at a minimum, filenames,
user names, group names, and link pathnames. Implementations may wish
to have localized extended keywords that use non-portable
characters.
.LP
The standard developers considered the following options:
.IP " *" 3
The archive creator specifies the well-defined name of the source
codeset. The receiver must then recognize the codeset name and
perform the appropriate translations to the destination codeset.
.LP
.IP " *" 3
The archive creator includes within the archive the character mapping
table for the source codeset used to encode extended
header records. The receiver must then read the character mapping
table and perform the appropriate translations to the destination
codeset.
.LP
.IP " *" 3
The archive creator translates the extended header records in the
source codeset into a canonical form. The receiver must then
perform the appropriate translations to the destination codeset.
.LP
.LP
The approach that incorporates the name of the source codeset poses
the problem of codeset name registration, and makes the
archive useless to \fIpax\fP archive decoders that do not recognize
that codeset.
.LP
Because parts of an archive may be corrupted, the standard developers
felt that including the character map of the source
codeset was too fragile. The loss of this one key component could
result in making the entire archive useless. (The difference
between this and the global extended header decision was that the
latter has a workaround-duplicating extended header records on
unreliable media-but this would be too burdensome for large character
set maps.)
.LP
Both of the above approaches also put an undue burden on the \fIpax\fP
archive receiver to handle the cross-product of all
source and destination codesets.
.LP
To simplify the translation from the source codeset to the canonical
form and from the canonical form to the destination
codeset, the standard developers decided that the internal representation
should be a stateless encoding. A stateless encoding is
one where each codepoint has the same meaning, without regard to the
decoder being in a specific state. An example of a stateful
encoding would be the Japanese Shift-JIS; an example of a stateless
encoding would be the ISO/IEC\ 646:1991 standard
(equivalent to 7-bit ASCII).
.LP
For these reasons, the standard developers decided to adopt a canonical
format for the representation of file information
strings. The obvious, well-endorsed candidate is the ISO/IEC\ 10646-1:2000
standard (based in part on Unicode), which can be
used to represent the characters of virtually all standardized character
sets. The standard developers initially agreed upon using
UCS2 (16-bit Unicode) as the internal representation. This repertoire
of characters provides a sufficiently rich set to represent
all commonly-used codesets.
.LP
However, the standard developers found that the 16-bit Unicode representation
had some problems. It forced the issue of
standardizing byte ordering. The 2-byte length of each character made
the extended header records twice as long for the case of
strings coded entirely from historical 7-bit ASCII. For these reasons,
the standard developers chose the UTF-8 defined in the
ISO/IEC\ 10646-1:2000 standard. This multi-byte representation encodes
UCS2 or UCS4 characters reliably and deterministically,
eliminating the need for a canonical byte ordering. In addition, NUL
octets and other characters possibly confusing to POSIX file
systems do not appear, except to represent themselves. It was realized
that certain national codesets take up more space after the
encoding, due to their placement within the UCS range; it was felt
that the usefulness of the encoding of the names outweighs the
disadvantage of size increase for file, user, and group names.
.LP
The encoding of UTF-8 is as follows:
.sp
.RS
.nf

\fBUCS4 Hex Encoding  UTF-8 Binary Encoding
.sp

00000000-0000007F  0xxxxxxx
00000080-000007FF  110xxxxx 10xxxxxx
00000800-0000FFFF  1110xxxx 10xxxxxx 10xxxxxx
00010000-001FFFFF  11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
00200000-03FFFFFF  111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
04000000-7FFFFFFF  1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
\fP
.fi
.RE
.LP
where each \fB'x'\fP represents a bit value from the character being
translated.
.SS ustar Interchange Format
.LP
The description of the \fBustar\fP format reflects numerous enhancements
over pre-1988 versions of the historical \fItar\fP
utility. The goal of these changes was not only to provide the functional
enhancements desired, but also to retain compatibility
between new and old versions. This compatibility has been retained.
Archives written using the old archive format are compatible
with the new format.
.LP
Implementors should be aware that the previous file format did not
include a mechanism to archive directory type files. For this
reason, the convention of using a filename ending with slash was adopted
to specify a directory on the archive.
.LP
The total size of the \fIname\fP and \fIprefix\fP fields have been
set to meet the minimum requirements for {PATH_MAX}. If a
pathname will fit within the \fIname\fP field, it is recommended that
the pathname be stored there without the use of the
\fIprefix\fP field. Although the name field is known to be too small
to contain {PATH_MAX} characters, the value was not changed
in this version of the archive file format to retain backwards-compatibility,
and instead the prefix was introduced. Also, because
of the earlier version of the format, there is no way to remove the
restriction on the \fIlinkname\fP field being limited in size
to just that of the \fIname\fP field.
.LP
The \fIsize\fP field is required to be meaningful in all implementation
extensions, although it could be zero. This is required
so that the data blocks can always be properly counted.
.LP
It is suggested that if device special files need to be represented
that cannot be represented in the standard format, that one
of the extension types ( \fBA\fP- \fBZ\fP) be used, and that the additional
information for the special file be represented as
data and be reflected in the \fIsize\fP field.
.LP
Attempting to restore a special file type, where it is converted to
ordinary data and conflicts with an existing filename, need
not be specially detected by the utility. If run as an ordinary user,
\fIpax\fP should not be able to overwrite the entries in,
for example, \fB/dev\fP in any case (whether the file is converted
to another type or not). If run as a privileged user, it should
be able to do so, and it would be considered a bug if it did not.
The same is true of ordinary data files and similarly named
special files; it is impossible to anticipate the needs of the user
(who could really intend to overwrite the file), so the
behavior should be predictable (and thus regular) and rely on the
protection system as required.
.LP
The value 7 in the \fItypeflag\fP field is intended to define how
contiguous files can be stored in a \fBustar\fP archive.
IEEE\ Std\ 1003.1-2001 does not require the contiguous file extension,
but does define a standard way of archiving such
files so that all conforming systems can interpret these file types
in a meaningful and consistent manner. On a system that does
not support extended file types, the \fIpax\fP utility should do the
best it can with the file and go on to the next.
.LP
The file protection modes are those conventionally used by the \fIls\fP
utility. This is
extended beyond the usage in the ISO\ POSIX-2 standard to support
the "shared text" or "sticky" bit. It is intended that
the conformance document should not document anything beyond the existence
of and support of such a mode. Further extensions are
expected to these bits, particularly with overloading the set-user-ID
and set-group-ID flags.
.SS cpio Interchange Format
.LP
The reference to appropriate privilege in the \fBcpio\fP format refers
to an error on standard output; the \fBustar\fP format
does not make comparable statements.
.LP
The model for this format was the historical System V \fIcpio\fP \fB-c\fP
data interchange format. This model documents the
portable version of the \fBcpio\fP format and not the binary version.
It has the flexibility to transfer data of any type
described within IEEE\ Std\ 1003.1-2001, yet is extensible to transfer
data types specific to extensions beyond
IEEE\ Std\ 1003.1-2001 (for example, contiguous files). Because it
describes existing practice, there is no question of
maintaining upwards-compatibility.
.SS cpio Header
.LP
There has been some concern that the size of the \fIc_ino\fP field
of the header is too small to handle those systems that have
very large \fIinode\fP numbers. However, the \fIc_ino\fP field in
the header is used strictly as a hard-link resolution mechanism
for archives. It is not necessarily the same value as the \fIinode\fP
number of the file in the location from which that file is
extracted.
.LP
The name \fIc_magic\fP is based on historical usage.
.SS cpio Filename
.LP
For most historical implementations of the \fIcpio\fP utility, {PATH_MAX}
octets can be used to describe the pathname without
the addition of any other header fields (the NUL character would be
included in this count). {PATH_MAX} is the minimum value for
pathname size, documented as 256 bytes. However, an implementation
may use \fIc_namesize\fP to determine the exact length of the
pathname. With the current description of the \fI<cpio.h>\fP header,
this pathname
size can be as large as a number that is described in six octal digits.
.LP
Two values are documented under the \fIc_mode\fP field values to provide
for extensibility for known file types:
.TP 7
\fB0110\ 000\fP
Reserved for contiguous files. The implementation may treat the rest
of the information for this archive like a regular file.
If this file type is undefined, the implementation may create the
file as a regular file.
.sp
.LP
This provides for extensibility of the \fBcpio\fP format while allowing
for the ability to read old archives. Files of an
unknown type may be read as "regular files" on some implementations.
On a system that does not support extended file types, the
\fIpax\fP utility should do the best it can with the file and go on
to the next.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIShell Command Language\fP , \fIcp\fP , \fIed\fP , \fIgetopts\fP
, \fIls\fP , \fIprintf\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<cpio.h>\fP, the System Interfaces volume of IEEE\ Std\ 1003.1-2001,
\fIchown\fP(), \fIcreat\fP(), \fImkdir\fP(), \fImkfifo\fP(), \fIstat\fP(),
\fIutime\fP(), \fIwrite\fP()
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .