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

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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 direc-
	      tory 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 implementa-
	      tion 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.
");
		  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
", 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 implementa-
       tions 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 Technol-
       ogy -- 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 .

IEEE
/The Open Group						       2003								UNLINK(3P)