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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 ||
	   _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.	  They	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 an unpriv‐
       ileged 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 filesystem, 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 filesystem.

       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 be used only by the superuser (that is, ordinary
       users cannot give away files).

NOTES
       The original Linux chown(), fchown(), and lchown()  system  calls  sup‐
       ported  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  filesystem user ID of the creating
       process.	 The group of the file depends on a range of factors,  includ‐
       ing  the	 type of filesystem, the options used to mount the filesystem,
       and whether or not the set-group-ID permission bit is  enabled  on  the
       parent directory.  If the filesystem supports the -o grpid (or, synony‐
       mously -o bsdgroups) and -o nogrpid  (or,  synonymously	-o sysvgroups)
       mount(8) options, then the rules are as follows:

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

       * If the filesystem 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 filesystem GID.

       * If the filesystem 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.	Filesystems that don't support
       these mount options follow the -o nogrpid rules.

       The chown() semantics are  deliberately	violated  on  NFS  filesystems
       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);
	   }

	   exit(EXIT_SUCCESS);
       }

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

COLOPHON
       This  page  is  part of release 3.54 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				  2010-11-22			      CHOWN(2)
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