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diff --git a/man-pages-posix-2017/man3p/unlink.3p b/man-pages-posix-2017/man3p/unlink.3p new file mode 100644 index 0000000..ee7069a --- /dev/null +++ b/man-pages-posix-2017/man3p/unlink.3p @@ -0,0 +1,455 @@ +'\" et +.TH UNLINK "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 +unlink, unlinkat +\(em remove a directory entry +.SH SYNOPSIS +.LP +.nf +#include <unistd.h> +.P +int unlink(const char *\fIpath\fP); +.P +#include <fcntl.h> +.P +int unlinkat(int \fIfd\fP, const char *\fIpath\fP, int \fIflag\fP); +.fi +.SH DESCRIPTION +The +\fIunlink\fR() +function shall remove a link to a file. If +.IR path +names a symbolic link, +\fIunlink\fR() +shall remove the symbolic link named by +.IR path +and shall not affect any file or directory named by the contents of the +symbolic link. Otherwise, +\fIunlink\fR() +shall remove the link named by the pathname pointed to by +.IR path +and shall decrement the link count of the file referenced by the link. +.P +When the file's link count becomes 0 and no process has the file open, +the space occupied by the file shall be freed and the file shall no +longer be accessible. If one or more processes have the file open when +the last link is removed, the link shall be removed before +\fIunlink\fR() +returns, but the removal of the file contents shall be postponed until +all references to the file are closed. +.P +The +.IR path +argument shall not name a directory unless the process has appropriate +privileges and the implementation supports using +\fIunlink\fR() +on directories. +.P +Upon successful completion, +\fIunlink\fR() +shall mark for update the last data modification and last file status +change timestamps of the parent directory. Also, if the file's link +count is not 0, the last file status change timestamp of the file shall +be marked for update. +.P +The +\fIunlinkat\fR() +function shall be equivalent to the +\fIunlink\fR() +or +\fIrmdir\fR() +function except in the case where +.IR path +specifies a relative path. In this case the directory entry to be +removed 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_REMOVEDIR 6 +.br +Remove the directory entry specified by +.IR fd +and +.IR path +as a directory, not a normal file. +.P +If +\fIunlinkat\fR() +is passed the special value AT_FDCWD in the +.IR fd +parameter, the current working directory shall be used and the behavior +shall be identical to a call to +\fIunlink\fR() +or +\fIrmdir\fR() +respectively, depending on whether or not the AT_REMOVEDIR bit is set in +.IR flag . +.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, the named file shall not +be changed. +.SH ERRORS +These functions shall fail and shall not unlink the file if: +.TP +.BR EACCES +Search permission is denied for a component of the path prefix, or +write permission is denied on the directory containing the directory +entry to be removed. +.TP +.BR EBUSY +The file named by the +.IR path +argument cannot be unlinked because it is being used by the system or +another process and the implementation considers this an error. +.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 file named by +.IR path +is a directory, and either the calling process does not have +appropriate privileges, or the implementation prohibits using +\fIunlink\fR() +on directories. +.TP +.BR EPERM " or " EACCES +.br +The S_ISVTX flag is set on the directory containing the file referred +to by the +.IR path +argument and the process does not satisfy the criteria specified in the Base Definitions volume of POSIX.1\(hy2017, +.IR "Section 4.3" ", " "Directory Protection". +.TP +.BR EROFS +The directory entry to be unlinked is part of a read-only file system. +.P +The +\fIunlinkat\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. +.TP +.BR EEXIST " or " ENOTEMPTY +.br +The +.IR flag +parameter has the AT_REMOVEDIR bit set and the +.IR path +argument names a directory that is not an empty directory, or there are +hard links to the directory other than dot or a single entry in dot-dot. +.TP +.BR ENOTDIR +The +.IR flag +parameter has the AT_REMOVEDIR bit set and +.IR path +does not name a directory. +.P +These functions may fail and not unlink the file if: +.TP +.BR EBUSY +The file named by +.IR path +is a named STREAM. +.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}. +.TP +.BR ETXTBSY +The entry to be unlinked is the last directory entry to a pure +procedure (shared text) file that is being executed. +.br +.P +The +\fIunlinkat\fR() +function may fail if: +.TP +.BR EINVAL +The value of the +.IR flag +argument is not valid. +.LP +.IR "The following sections are informative." +.SH EXAMPLES +.SS "Removing a Link to a File" +.P +The following example shows how to remove a link to a file named +.BR /home/cnd/mod1 +by removing the entry named +.BR /modules/pass1 . +.sp +.RS 4 +.nf + +#include <unistd.h> +.P +char *path = "/modules/pass1"; +int status; +\&... +status = unlink(path); +.fi +.P +.RE +.SS "Checking for an Error" +.P +The following example fragment creates a temporary password lock file +named +.BR LOCKFILE , +which is defined as +.BR /etc/ptmp , +and gets a file descriptor for it. If the file cannot be opened for +writing, +\fIunlink\fR() +is used to remove the link between the file descriptor and +.BR LOCKFILE . +.sp +.RS 4 +.nf + +#include <sys/types.h> +#include <stdio.h> +#include <fcntl.h> +#include <errno.h> +#include <unistd.h> +#include <sys/stat.h> +.P +#define LOCKFILE "/etc/ptmp" +.P +int pfd; /* Integer for file descriptor returned by open call. */ +FILE *fpfd; /* File pointer for use in putpwent(). */ +\&... +/* Open password Lock file. If it exists, this is an error. */ +if ((pfd = open(LOCKFILE, O_WRONLY| O_CREAT | O_EXCL, S_IRUSR + | S_IWUSR | S_IRGRP | S_IROTH)) == -1) { + fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\en"); + exit(1); +} +.P +/* Lock file created; proceed with fdopen of lock file so that + putpwent() can be used. + */ +if ((fpfd = fdopen(pfd, "w")) == NULL) { + close(pfd); + unlink(LOCKFILE); + exit(1); +} +.fi +.P +.RE +.SS "Replacing Files" +.P +The following example fragment uses +\fIunlink\fR() +to discard links to files, so that they can be replaced with new +versions of the files. The first call removes the link to +.BR LOCKFILE +if an error occurs. Successive calls remove the links to +.BR SAVEFILE +and +.BR PASSWDFILE +so that new links can be created, then removes the link to +.BR LOCKFILE +when it is no longer needed. +.sp +.RS 4 +.nf + +#include <sys/types.h> +#include <stdio.h> +#include <fcntl.h> +#include <errno.h> +#include <unistd.h> +#include <sys/stat.h> +.P +#define LOCKFILE "/etc/ptmp" +#define PASSWDFILE "/etc/passwd" +#define SAVEFILE "/etc/opasswd" +\&... +/* If no change was made, assume error and leave passwd unchanged. */ +if (!valid_change) { + fprintf(stderr, "Could not change password for user %s\en", user); + unlink(LOCKFILE); + exit(1); +} +.P +/* Change permissions on new password file. */ +chmod(LOCKFILE, S_IRUSR | S_IRGRP | S_IROTH); +.P +/* Remove saved password file. */ +unlink(SAVEFILE); +.P +/* Save current password file. */ +link(PASSWDFILE, SAVEFILE); +.P +/* Remove current password file. */ +unlink(PASSWDFILE); +.P +/* Save new password file as current password file. */ +link(LOCKFILE,PASSWDFILE); +.P +/* Remove lock file. */ +unlink(LOCKFILE); +.P +exit(0); +.fi +.P +.RE +.SH "APPLICATION USAGE" +Applications should use +\fIrmdir\fR() +to remove a directory. +.SH RATIONALE +Unlinking a directory is restricted to the superuser +in many historical implementations for reasons given in +\fIlink\fR() +(see also +\fIrename\fR()). +.P +The meaning of +.BR [EBUSY] +in historical implementations is ``mount point busy''. Since this volume of POSIX.1\(hy2017 does +not cover the system administration concepts of mounting and unmounting, +the description of the error was changed to ``resource busy''. (This +meaning is used by some device drivers when a second process tries to +open an exclusive use device.) The wording is also intended to allow +implementations to refuse to remove a directory if it is the root or +current working directory of any process. +.P +The standard developers reviewed TR 24715\(hy2006 and noted that +LSB-conforming implementations may return +.BR [EISDIR] +instead of +.BR [EPERM] +when unlinking a directory. A change to permit this behavior by +changing the requirement for +.BR [EPERM] +to +.BR [EPERM] +or +.BR [EISDIR] +was considered, but decided against since it would break existing +strictly conforming and conforming applications. Applications written +for portability to both POSIX.1\(hy2008 and the LSB should be prepared to +handle either error code. +.P +The purpose of the +\fIunlinkat\fR() +function is to remove directory entries 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 +\fIunlink\fR(), +resulting in unspecified behavior. By opening a file descriptor for +the target directory and using the +\fIunlinkat\fR() +function it can be guaranteed that the removed directory entry is +located relative to the desired directory. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "\fIclose\fR\^(\|)", +.IR "\fIlink\fR\^(\|)", +.IR "\fIremove\fR\^(\|)", +.IR "\fIrename\fR\^(\|)", +.IR "\fIrmdir\fR\^(\|)", +.IR "\fIsymlink\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2017, +.IR "Section 4.3" ", " "Directory Protection", +.IR "\fB<fcntl.h>\fP", +.IR "\fB<unistd.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 . |