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           #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 ||
               || /* 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
           * 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 are changed by an unpriv-
           ileged 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-
           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
           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.


           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.
           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  pro-
           cess.   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.
           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) {


           chmod(2), flock(2), path_resolution(7), symlink(7)

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