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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

           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 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

       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  ver‐
       sion.   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().

       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 inter‐
       preted 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 val‐

       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, fchownat() dereferences symbolic  links,  like

       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_res‐

       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 addi‐
       tional 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 ver‐
       sion 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,  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  fol‐

       * 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

       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

   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 symbolic link in /proc/self/fd that corresponds to the  dirfd  argu‐

       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.

   Historical details
       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(), sup‐
       porting 32-bit IDs.  The glibc chown(), fchown(), and lchown() wrapper functions transpar‐
       ently 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 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>

       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 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.

Linux                                       2014-08-19                                   CHOWN(2)

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