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



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

SYNOPSIS
       #include <unistd.h>

       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 arbitrarily.

       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  sys-
       tem  user  ID of the creating process.  The group of the file depends on a range of factors, including 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, synonymously -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 supported 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.   Addition-
       ally,  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  ownership  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 command-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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-16                          CHOWN(2)