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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 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

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  an  unprivileged  user  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

       The original Linux chown(), fchown(), and lchown() system calls supported only 16-bit user
       and  group  IDs.   Subsequently,  Linux  2.4  added chown32(), fchown32(), and lchown32(),
       supporting 32-bit IDs.  The  glibc  chown(),  fchown(),  and  lchown()  wrapper  functions
       transparently deal with the variations across kernel versions.

       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, 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.   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 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);
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO

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

COLOPHON

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