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NAME

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

SYNOPSIS

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

       fchownat():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE

DESCRIPTION

       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
       specified:

       * 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
       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().

   fchownat()
       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.

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

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

RETURN VALUE

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

ERRORS

       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.

       ENAMETOOLONG
              pathname 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.

       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.

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

VERSIONS

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

CONFORMING TO

       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.

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  filesystem user ID of the creating
       process.  The group  of  the  file  depends  on  a  range  of  factors,
       including  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,   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
       supported 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
       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).

   Program source
       #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] == '') {
               fprintf(stderr, "%s <owner> <file>
", argv[0]);
               exit(EXIT_FAILURE);
           }

           uid = strtol(argv[1], &endptr, 10);  /* Allow a numeric string */

           if (*endptr != '') {         /* 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), flock(2), path_resolution(7), symlink(7)

COLOPHON

       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/.



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