unlink(3p) — Linux manual page


UNLINK(3P)              POSIX Programmer's Manual             UNLINK(3P)

PROLOG         top

       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.

NAME         top

       unlink, unlinkat — remove a directory entry

SYNOPSIS         top

       #include <unistd.h>

       int unlink(const char *path);

       #include <fcntl.h>

       int unlinkat(int fd, const char *path, int flag);

DESCRIPTION         top

       The unlink() function shall remove a link to a file. If path
       names a symbolic link, unlink() shall remove the symbolic link
       named by path and shall not affect any file or directory named by
       the contents of the symbolic link. Otherwise, unlink() shall
       remove the link named by the pathname pointed to by path and
       shall decrement the link count of the file referenced by the

       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 unlink() returns, but the removal of the file
       contents shall be postponed until all references to the file are

       The path argument shall not name a directory unless the process
       has appropriate privileges and the implementation supports using
       unlink() on directories.

       Upon successful completion, unlink() 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.

       The unlinkat() function shall be equivalent to the unlink() or
       rmdir() function except in the case where 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 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.

       Values for flag are constructed by a bitwise-inclusive OR of
       flags from the following list, defined in <fcntl.h>:

             Remove the directory entry specified by fd and path as a
             directory, not a normal file.

       If unlinkat() is passed the special value AT_FDCWD in the fd
       parameter, the current working directory shall be used and the
       behavior shall be identical to a call to unlink() or rmdir()
       respectively, depending on whether or not the AT_REMOVEDIR bit is
       set in flag.

RETURN VALUE         top

       Upon successful completion, these functions shall return 0.
       Otherwise, these functions shall return -1 and set errno to
       indicate the error. If -1 is returned, the named file shall not
       be changed.

ERRORS         top

       These functions shall fail and shall not unlink the file if:

       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.

       EBUSY  The file named by the path argument cannot be unlinked
              because it is being used by the system or another process
              and the implementation considers this an error.

       ELOOP  A loop exists in symbolic links encountered during
              resolution of the path argument.

              The length of a component of a pathname is longer than

       ENOENT A component of path does not name an existing file or path
              is an empty string.

              A component of the path prefix names an existing file that
              is neither a directory nor a symbolic link to a directory,
              or the path argument contains at least one non-<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.

       EPERM  The file named by path is a directory, and either the
              calling process does not have appropriate privileges, or
              the implementation prohibits using unlink() on

       EPERM or EACCES
              The S_ISVTX flag is set on the directory containing the
              file referred to by the path argument and the process does
              not satisfy the criteria specified in the Base Definitions
              volume of POSIX.1‐2017, Section 4.3, Directory Protection.

       EROFS  The directory entry to be unlinked is part of a read-only
              file system.

       The unlinkat() function shall fail if:

       EACCES The access mode of the open file description associated
              with fd is not O_SEARCH and the permissions of the
              directory underlying fd do not permit directory searches.

       EBADF  The path argument does not specify an absolute path and
              the fd argument is neither AT_FDCWD nor a valid file
              descriptor open for reading or searching.

              The path argument is not an absolute path and fd is a file
              descriptor associated with a non-directory file.

              The flag parameter has the AT_REMOVEDIR bit set and the
              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.

              The flag parameter has the AT_REMOVEDIR bit set and path
              does not name a directory.

       These functions may fail and not unlink the file if:

       EBUSY  The file named by path is a named STREAM.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered
              during resolution of the path argument.

              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}.

              The entry to be unlinked is the last directory entry to a
              pure procedure (shared text) file that is being executed.

       The unlinkat() function may fail if:

       EINVAL The value of the flag argument is not valid.

       The following sections are informative.

EXAMPLES         top

   Removing a Link to a File
       The following example shows how to remove a link to a file named
       /home/cnd/mod1 by removing the entry named /modules/pass1.

           #include <unistd.h>

           char *path = "/modules/pass1";
           int   status;
           status = unlink(path);

   Checking for an Error
       The following example fragment creates a temporary password lock
       file named LOCKFILE, which is defined as /etc/ptmp, and gets a
       file descriptor for it. If the file cannot be opened for writing,
       unlink() is used to remove the link between the file descriptor
       and LOCKFILE.

           #include <sys/types.h>
           #include <stdio.h>
           #include <fcntl.h>
           #include <errno.h>
           #include <unistd.h>
           #include <sys/stat.h>

           #define LOCKFILE "/etc/ptmp"

           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.\n");

           /* Lock file created; proceed with fdopen of lock file so that
              putpwent() can be used.
           if ((fpfd = fdopen(pfd, "w")) == NULL) {

   Replacing Files
       The following example fragment uses unlink() to discard links to
       files, so that they can be replaced with new versions of the
       files. The first call removes the link to LOCKFILE if an error
       occurs. Successive calls remove the links to SAVEFILE and
       PASSWDFILE so that new links can be created, then removes the
       link to LOCKFILE when it is no longer needed.

           #include <sys/types.h>
           #include <stdio.h>
           #include <fcntl.h>
           #include <errno.h>
           #include <unistd.h>
           #include <sys/stat.h>

           #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\n", user);

           /* Change permissions on new password file. */
           chmod(LOCKFILE, S_IRUSR | S_IRGRP | S_IROTH);

           /* Remove saved password file. */

           /* Save current password file. */
           link(PASSWDFILE, SAVEFILE);

           /* Remove current password file. */

           /* Save new password file as current password file. */

           /* Remove lock file. */



       Applications should use rmdir() to remove a directory.

RATIONALE         top

       Unlinking a directory is restricted to the superuser in many
       historical implementations for reasons given in link() (see also

       The meaning of [EBUSY] in historical implementations is ``mount
       point busy''. Since this volume of POSIX.1‐2017 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

       The standard developers reviewed TR 24715‐2006 and noted that
       LSB-conforming implementations may return [EISDIR] instead of
       [EPERM] when unlinking a directory. A change to permit this
       behavior by changing the requirement for [EPERM] to [EPERM] or
       [EISDIR] was considered, but decided against since it would break
       existing strictly conforming and conforming applications.
       Applications written for portability to both POSIX.1‐2008 and the
       LSB should be prepared to handle either error code.

       The purpose of the unlinkat() 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 unlink(),
       resulting in unspecified behavior. By opening a file descriptor
       for the target directory and using the unlinkat() function it can
       be guaranteed that the removed directory entry is located
       relative to the desired directory.



SEE ALSO         top

       close(3p), link(3p), remove(3p), rename(3p), rmdir(3p),

       The Base Definitions volume of POSIX.1‐2017, Section 4.3,
       Directory Protection, fcntl.h(0p), unistd.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                        UNLINK(3P)

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