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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():
	   /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
	       || _XOPEN_SOURCE >= 500
	       || /* Glibc versions <= 2.19: */ _BSD_SOURCE

	   Since glibc 2.10:
	       _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 is changed by an unprivi-
       leged 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.

       EPERM  The   file   is	marked	 immutable   or	  append-only.	  (See

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

       The general errors for fchown() are listed below:

       EBADF  fd is not a valid open file descriptor.

       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.

   Ownership of new files
       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 mode bit is enabled on  the	parent
       directory.   If	the filesystem 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  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.

   Glibc notes
       On older kernels where fchownat() is  unavailable,  the	glibc  wrapper
       function	 falls back to the use of chown() and lchown().	 When pathname
       is a relative pathname, glibc constructs a pathname based on  the  sym-
       bolic link in /proc/self/fd that corresponds to the dirfd argument.

       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.

   Historical details
       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.

       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) {


       chgrp(1), chown(1), chmod(2), flock(2), path_resolution(7), symlink(7)

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Linux				  2016-12-12			      CHOWN(2)