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       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 <= 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 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 is 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,  and  since  Linux  2.2.13,  root is treated like other users.  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().

       When  the  owner  or  group of an executable file is changed (by any user), all capability
       sets for the file are cleared.

       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

       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

       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 to indicate  the


       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

       EBADF  (fchown()) fd is not a valid open file descriptor.

       EBADF  (fchownat()) pathname is relative but dirfd is neither AT_FDCWD nor  a  valid  file

       EFAULT pathname points outside your accessible address space.

       EINVAL (fchownat()) Invalid flag specified in flags.

       EIO    (fchown()) A low-level I/O error occurred while modifying the inode.

       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.

              (fchownat())  pathname  is  relative  and dirfd is a file descriptor referring to a
              file other than 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 ioctl_iflags(2).)

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


       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,  including  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

       * 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 4.12, 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

       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(),
       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 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) {



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


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