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diff --git a/man-pages-posix-2017/man3p/chmod.3p b/man-pages-posix-2017/man3p/chmod.3p new file mode 100644 index 0000000..13ea518 --- /dev/null +++ b/man-pages-posix-2017/man3p/chmod.3p @@ -0,0 +1,372 @@ +'\" et +.TH CHMOD "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual" +.\" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. +.\" +.SH NAME +chmod, fchmodat +\(em change mode of a file +.SH SYNOPSIS +.LP +.nf +#include <sys/stat.h> +.P +int chmod(const char *\fIpath\fP, mode_t \fImode\fP); +.P +#include <fcntl.h> +.P +int fchmodat(int \fIfd\fP, const char *\fIpath\fP, mode_t \fImode\fP, int \fIflag\fP); +.fi +.SH DESCRIPTION +The +\fIchmod\fR() +function shall change S_ISUID, S_ISGID, +S_ISVTX, +and the file permission bits of the file named by the pathname pointed +to by the +.IR path +argument to the corresponding bits in the +.IR mode +argument. The application shall ensure that the effective user ID +of the process matches the owner of the file or the process has +appropriate privileges in order to do this. +.P +S_ISUID, S_ISGID, +S_ISVTX, +and the file permission bits +are described in +.IR <sys/stat.h> . +.P +If the calling process does not have appropriate privileges, and if the +group ID of the file does not match the effective group ID or one of +the supplementary group IDs and if the file is a regular file, bit +S_ISGID (set-group-ID on execution) in the file's mode shall be cleared +upon successful return from +\fIchmod\fR(). +.P +Additional implementation-defined restrictions may cause the S_ISUID +and S_ISGID bits in +.IR mode +to be ignored. +.P +Upon successful completion, +\fIchmod\fR() +shall mark for update the last file status change timestamp of the file. +.P +The +\fIfchmodat\fR() +function shall be equivalent to the +\fIchmod\fR() +function except in the case where +.IR path +specifies a relative path. In this case the file to be changed is +determined relative to the directory associated with the file +descriptor +.IR fd +instead of the current working directory. If the access mode of the +open file description associated with the file descriptor is not +O_SEARCH, the function shall check whether directory searches +are permitted using the current permissions of the directory +underlying the file descriptor. If the access mode is +O_SEARCH, the function shall not perform the check. +.P +Values for +.IR flag +are constructed by a bitwise-inclusive OR of flags from the following +list, defined in +.IR <fcntl.h> : +.IP AT_SYMLINK_NOFOLLOW 6 +.br +If +.IR path +names a symbolic link, then the mode of the symbolic link is changed. +.P +If +\fIfchmodat\fR() +is passed the special value AT_FDCWD in the +.IR fd +parameter, the current working directory shall be used. If also +.IR flag +is zero, the behavior shall be identical to a call to +\fIchmod\fR(). +.SH "RETURN VALUE" +Upon successful completion, these functions shall return 0. +Otherwise, these functions shall return \-1 and set +.IR errno +to indicate the error. If \-1 is returned, no change to the +file mode occurs. +.SH ERRORS +These functions shall fail if: +.TP +.BR EACCES +Search permission is denied on a component of the path prefix. +.TP +.BR ELOOP +A loop exists in symbolic links encountered during resolution of the +.IR path +argument. +.TP +.BR ENAMETOOLONG +.br +The length of a component of a pathname is longer than +{NAME_MAX}. +.TP +.BR ENOENT +A component of +.IR path +does not name an existing file or +.IR path +is an empty string. +.TP +.BR ENOTDIR +A component of the path prefix names an existing file that is neither +a directory nor a symbolic link to a directory, or the +.IR path +argument contains at least one non-\c +<slash> +character and ends with one or more trailing +<slash> +characters and the last pathname component names an existing file +that is neither a directory nor a symbolic link to a directory. +.TP +.BR EPERM +The effective user ID does not match the owner of the file and the +process does not have appropriate privileges. +.TP +.BR EROFS +The named file resides on a read-only file system. +.P +The +\fIfchmodat\fR() +function shall fail if: +.TP +.BR EACCES +The access mode of the open file description associated with +.IR fd +is not O_SEARCH and the permissions of the directory underlying +.IR fd +do not permit directory searches. +.TP +.BR EBADF +The +.IR path +argument does not specify an absolute path and the +.IR fd +argument is neither AT_FDCWD nor a valid file descriptor open +for reading or searching. +.TP +.BR ENOTDIR +The +.IR path +argument is not an absolute path and +.IR fd +is a file descriptor associated with a non-directory file. +.P +These functions may fail if: +.TP +.BR EINTR +A signal was caught during execution of the function. +.TP +.BR EINVAL +The value of the +.IR mode +argument is invalid. +.TP +.BR ELOOP +More than +{SYMLOOP_MAX} +symbolic links were encountered during resolution of the +.IR path +argument. +.TP +.BR ENAMETOOLONG +.br +The length of a pathname exceeds +{PATH_MAX}, +or pathname resolution of a symbolic link produced an intermediate +result with a length that exceeds +{PATH_MAX}. +.P +The +\fIfchmodat\fR() +function may fail if: +.TP +.BR EINVAL +The value of the +.IR flag +argument is invalid. +.TP +.BR EOPNOTSUPP +The AT_SYMLINK_NOFOLLOW bit is set in the +.IR flag +argument, +.IR path +names a symbolic link, and the system does not support changing the +mode of a symbolic link. +.br +.LP +.IR "The following sections are informative." +.SH EXAMPLES +.SS "Setting Read Permissions for User, Group, and Others" +.P +The following example sets read permissions for the owner, group, and +others. +.sp +.RS 4 +.nf + +#include <sys/stat.h> +.P +const char *path; +\&... +chmod(path, S_IRUSR|S_IRGRP|S_IROTH); +.fi +.P +.RE +.SS "Setting Read, Write, and Execute Permissions for the Owner Only" +.P +The following example sets read, write, and execute permissions for the +owner, and no permissions for group and others. +.sp +.RS 4 +.nf + +#include <sys/stat.h> +.P +const char *path; +\&... +chmod(path, S_IRWXU); +.fi +.P +.RE +.SS "Setting Different Permissions for Owner, Group, and Other" +.P +The following example sets owner permissions for CHANGEFILE to read, +write, and execute, group permissions to read and execute, and other +permissions to read. +.sp +.RS 4 +.nf + +#include <sys/stat.h> +.P +#define CHANGEFILE "/etc/myfile" +\&... +chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH); +.fi +.P +.RE +.SS "Setting and Checking File Permissions" +.P +The following example sets the file permission bits for a file named +.BR /home/cnd/mod1 , +then calls the +\fIstat\fR() +function to verify the permissions. +.sp +.RS 4 +.nf + +#include <sys/types.h> +#include <sys/stat.h> +.P +int status; +struct stat buffer +\&... +chmod("/home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH); +status = stat("/home/cnd/mod1", &buffer); +.fi +.P +.RE +.SH "APPLICATION USAGE" +In order to ensure that the S_ISUID and S_ISGID +bits are set, an application requiring this should use +\fIstat\fR() +after a successful +\fIchmod\fR() +to verify this. +.P +Any file descriptors currently open by any process on the file could +possibly become invalid if the mode of the file is changed to a value +which would deny access to that process. One situation where this could +occur is on a stateless file system. This behavior will not occur in a +conforming environment. +.SH RATIONALE +This volume of POSIX.1\(hy2017 specifies that the S_ISGID bit is cleared by +\fIchmod\fR() +on a regular file under certain conditions. This is specified on the +assumption that regular files may be executed, and the system should +prevent users from making executable +\fIsetgid\fR() +files perform with privileges that the caller does not have. On +implementations that support execution of other file types, the S_ISGID +bit should be cleared for those file types under the same +circumstances. +.P +Implementations that use the S_ISUID bit to indicate some other +function (for example, mandatory record locking) on non-executable +files need not clear this bit on writing. They should clear the bit +for executable files and any other cases where the bit grants special +powers to processes that change the file contents. Similar comments +apply to the S_ISGID bit. +.P +The purpose of the +\fIfchmodat\fR() +function is to enable changing the mode of files in directories other +than the current working directory without exposure to race conditions. +Any part of the path of a file could be changed in parallel to a call +to +\fIchmod\fR(), +resulting in unspecified behavior. By opening a file descriptor for +the target directory and using the +\fIfchmodat\fR() +function it can be guaranteed that the changed file is located relative +to the desired directory. Some implementations might allow changing +the mode of symbolic links. This is not supported by the interfaces in +the POSIX specification. Systems with such support provide an +interface named +.IR lchmod (\|). +To support such implementations +\fIfchmodat\fR() +has a +.IR flag +parameter. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "\fIaccess\fR\^(\|)", +.IR "\fIchown\fR\^(\|)", +.IR "\fIexec\fR\^", +.IR "\fIfstatat\fR\^(\|)", +.IR "\fIfstatvfs\fR\^(\|)", +.IR "\fImkdir\fR\^(\|)", +.IR "\fImkfifo\fR\^(\|)", +.IR "\fImknod\fR\^(\|)", +.IR "\fIopen\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2017, +.IR "\fB<fcntl.h>\fP", +.IR "\fB<sys_stat.h>\fP", +.IR "\fB<sys_types.h>\fP" +.\" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1-2017, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, 2018 Edition, +Copyright (C) 2018 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 . +.PP +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |