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NAME

       unlink - remove a directory entry

SYNOPSIS

       #include <unistd.h>

       int unlink(const char *path);

DESCRIPTION

       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 link.

       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 closed.

       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 st_ctime
       and st_mtime fields of the parent directory. Also, if the  file’s  link
       count  is  not  0,  the  st_ctime field of the file shall be marked for
       update.

RETURN VALUE

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

ERRORS

       The unlink() function 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.

       ENAMETOOLONG
              The length of the path argument exceeds {PATH_MAX} or a pathname
              component is longer than {NAME_MAX}.

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

       ENOTDIR
              A component of the path prefix is not 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 directories.

       EPERM or EACCES

              The  S_ISVTX  flag  is  set on the directory containing the file
              referred to by the path argument and the caller is not the  file
              owner,  nor  is  the  caller  the  directory owner, nor does the
              caller have appropriate privileges.

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

       The unlink() function 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.

       ENAMETOOLONG
              As a result of encountering a symbolic link in resolution of the
              path  argument,  the  length  of the substituted pathname string
              exceeded {PATH_MAX}.

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

       The following sections are informative.

EXAMPLES

   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");
                  exit(1);
              }

              /* 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);
              }

   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);
                  unlink(LOCKFILE);
                  exit(1);
              }

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

              /* Remove saved password file. */
              unlink(SAVEFILE);

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

              /* Remove current password file. */
              unlink(PASSWDFILE);

              /* Save new password file as current password file. */
              link(LOCKFILE,PASSWDFILE);

              /* Remove lock file. */
              unlink(LOCKFILE);

              exit(0);

APPLICATION USAGE

       Applications should use rmdir() to remove a directory.

RATIONALE

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

       The  meaning  of  [EBUSY] in historical implementations is "mount point
       busy". Since this volume of IEEE Std 1003.1-2001  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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       close() , link() , remove() , rmdir() , the Base Definitions volume  of
       IEEE Std 1003.1-2001, <unistd.h>

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 .