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

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

       #include <unistd.h>

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

       #include <fcntl.h>	    /* Definition of AT_* constants */
       #include <unistd.h>

       int fchownat(int dirfd, const char *pathname,
		    uid_t owner, gid_t group, int flags);

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

       fchown(), lchown():
	   _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
	   || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

	   Since glibc 2.10:
	       _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
	   Before glibc 2.10:

       These system calls change the owner and group of a file.	 The  chown(),
       fchown(),  and  lchown()	 system	 calls	differ only in how the file is

       * chown() changes the ownership of  the	file  specified	 by  pathname,
	 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‐

       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

       The fchownat() system call operates in exactly the same way as chown(),
       except for the differences described here.

       If  the	pathname given in pathname is relative, then it is interpreted
       relative to the directory referred to  by  the  file  descriptor	 dirfd
       (rather	than  relative to the current working directory of the calling
       process, as is done by chown() for a relative pathname).

       If pathname is relative and dirfd is the special value  AT_FDCWD,  then
       pathname	 is  interpreted  relative to the current working directory of
       the calling process (like chown()).

       If pathname is absolute, then dirfd is ignored.

       The flags argument is a bit mask created by ORing together 0 or more of
       the following values;

       AT_EMPTY_PATH (since Linux 2.6.39)
	      If  pathname is an empty string, operate on the file referred to
	      by dirfd (which may have been obtained using the open(2)	O_PATH
	      flag).   In  this case, dirfd can refer to any type of file, not
	      just a directory.	 If dirfd is AT_FDCWD, the  call  operates  on
	      the  current  working  directory.	  This flag is Linux-specific;
	      define _GNU_SOURCE to obtain its definition.

	      If pathname is a symbolic link, do not dereference  it:  instead
	      operate  on the link itself, like lchown().  (By default, fchow‐
	      nat() dereferences symbolic links, like chown().)

       See openat(2) for an explanation of the need for fchownat().

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

       Depending  on  the filesystem, errors other than those listed below 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 pathname points outside your accessible address space.

       ELOOP  Too many symbolic links were encountered in resolving pathname.

	      pathname is too long.

       ENOENT The file does not exist.

       ENOMEM Insufficient kernel memory was available.

	      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.

       The same errors that occur for chown() can also occur  for  fchownat().
       The following additional errors can occur for fchownat():

       EBADF  dirfd is not a valid file descriptor.

       EINVAL Invalid flag specified in flags.

	      pathname is relative and dirfd is a file descriptor referring to
	      a file other than a directory.

       fchownat() was added to Linux in kernel	2.6.16;	 library  support  was
       added to glibc in version 2.4.

       chown(), fchown(), lchown(): 4.4BSD, SVr4, POSIX.1-2001, POSIX.1-2008.

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

       fchownat(): POSIX.1-2008.

       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.

       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).

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

       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]);

	   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) {

	       uid = pwd->pw_uid;

	   if (chown(argv[2], uid, -1) == -1) {


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

       This  page  is  part of release 3.65 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				  2014-03-19			      CHOWN(2)

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