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



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

SYNOPSIS
       #include 

       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 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 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 system user ID of the creating pro-
       cess.  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  sup-
       ported  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	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 
       #include 
       #include 
       #include 

       int
       main(int argc, char *argv[])
       {
	   uid_t uid;
	   struct passwd *pwd;
	   char *endptr;

	   if (argc != 3 || argv[1][0] == '\0') {
	       fprintf(stderr, "%s  \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 information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux				  2008-06-16			      CHOWN(2)