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CHOWN(2)                   Linux Programmer's Manual                  CHOWN(2)



NAME
       chown, fchown, lchown - change ownership of a file

SYNOPSIS
       #include <&lt;unistd.h>&gt;

       int chown(const char *path, uid_t owner, gid_t group);
       int fchown(int fd, uid_t owner, gid_t group);
       int lchown(const char *path, uid_t owner, gid_t group);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       fchown(), lchown(): _BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION
       These  system  calls  change the owner and group of a file.  The differ
       only in how the file is specified:

       * chown() changes the ownership of the file specified by path, which is
         dereferenced if it is a symbolic link.

       * fchown()  changes  the  ownership of the file referred to by the open
         file descriptor fd.

       * lchown() is like chown(), but does not dereference symbolic links.

       Only a privileged process (Linux: one with  the  CAP_CHOWN  capability)
       may  change  the  owner  of a file.  The owner of a file may change the
       group of the file to any group of which that  owner  is  a  member.   A
       privileged  process  (Linux: with CAP_CHOWN) may change the group arbi-
       trarily.

       If the owner or group is specified as -1, then that ID is not changed.

       When the owner or group of an executable file are  changed  by  a  non-
       superuser,  the  S_ISUID and S_ISGID mode bits are cleared.  POSIX does
       not specify whether this also should happen when root does the chown();
       the  Linux  behavior  depends on the kernel version.  In case of a non-
       group-executable file (i.e., one for which the S_IXGRP bit is not  set)
       the  S_ISGID  bit  indicates mandatory locking, and is not cleared by a
       chown().

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

ERRORS
       Depending  on  the file system, other errors can be returned.  The more
       general errors for chown() are listed below.

       EACCES Search permission is denied on a component of the  path  prefix.
              (See also path_resolution(7).)

       EFAULT path points outside your accessible address space.

       ELOOP  Too many symbolic links were encountered in resolving path.

       ENAMETOOLONG
              path is too long.

       ENOENT The file does not exist.

       ENOMEM Insufficient kernel memory was available.

       ENOTDIR
              A component of the path prefix is not a directory.

       EPERM  The  calling  process did not have the required permissions (see
              above) to change owner and/or group.

       EROFS  The named file resides on a read-only file system.

       The general errors for fchown() are listed below:

       EBADF  The descriptor is not valid.

       EIO    A low-level I/O error occurred while modifying the inode.

       ENOENT See above.

       EPERM  See above.

       EROFS  See above.

CONFORMING TO
       4.4BSD, SVr4, POSIX.1-2001.

       The 4.4BSD version can only be used by the superuser (that is, ordinary
       users cannot give away files).

NOTES
       When  a new file is created (by, for example, open(2) or mkdir(2)), its
       owner is made the same as the file  system  user  ID  of  the  creating
       process.   The group of the file depends on a range of factors, includ-
       ing the type of file system, the options used to mount the file system,
       and  whether  or  not the set-group-ID permission bit is enabled on the
       parent directory.  If the file system supports the -o grpid  (or,  syn-
       onymously -o bsdgroups) and -o nogrpid (or, synonymously -o sysvgroups)
       mount(8) options, then the rules are as follows:

       * If the file system is mounted with -o grpid, then the group of a  new
         file is made the same as that of the parent directory.

       * If  the  file  system is mounted with -o nogrpid and the set-group-ID
         bit is disabled on the parent directory, then the group of a new file
         is made the same as the process's file system GID.

       * If  the  file  system is mounted with -o nogrpid and the set-group-ID
         bit is enabled on the parent directory, then the group of a new  file
         is made the same as that of the parent directory.

       As  at Linux 2.6.25, the -o grpid and -o nogrpid mount options are sup-
       ported by ext2, ext3, ext4, and XFS.  File systems that  don't  support
       these mount options follow the -o nogrpid rules.

       The  chown()  semantics  are  deliberately violated on NFS file systems
       which have UID mapping enabled.  Additionally,  the  semantics  of  all
       system  calls  which  access  the  file  contents are violated, because
       chown() may cause immediate access revocation on  already  open  files.
       Client  side  caching may lead to a delay between the time where owner-
       ship have been changed to allow access for a user and  the  time  where
       the file can actually be accessed by the user on other clients.

       In  versions  of  Linux  prior  to  2.1.81  (and distinct from 2.1.46),
       chown() did not follow symbolic links.   Since  Linux  2.1.81,  chown()
       does  follow  symbolic  links,  and there is a new system call lchown()
       that does not follow symbolic links.  Since Linux 2.1.86, this new call
       (that  has  the  same  semantics  as  the old chown()) has got the same
       syscall number, and chown() got the newly introduced number.

EXAMPLE
       The following program changes the ownership of the file  named  in  its
       second  command-line  argument to the value specified in its first com-
       mand-line argument.  The new owner can be specified either as a numeric
       user  ID,  or  as  a username (which is converted to a user ID by using
       getpwnam(3) to perform a lookup in the system password file).

       #include <pwd.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
           uid_t uid;
           struct passwd *pwd;
           char *endptr;

           if (argc != 3 || argv[1][0] == '\0') {
               fprintf(stderr, "%s <owner> <file>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           uid = strtol(argv[1], &endptr, 10);  /* Allow a numeric string */

           if (*endptr != '\0') {         /* Was not pure numeric string */
               pwd = getpwnam(argv[1]);   /* Try getting UID for username */
               if (pwd == NULL) {
                   perror("getpwnam");
                   exit(EXIT_FAILURE);
               }

               uid = pwd->pw_uid;
           }

           if (chown(argv[2], uid, -1) == -1) {
               perror("chown");
               exit(EXIT_FAILURE);
           } /* if */

           exit(EXIT_SUCCESS);
       } /* main */

SEE ALSO
       chmod(2), fchownat(2), flock(2), path_resolution(7), symlink(7)

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-16                          CHOWN(2)