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NAME

       chown, fchown, lchown - change ownership of a file

SYNOPSIS

       #include <unistd.h>

       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
       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 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
       process.  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
       supported  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
       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).

       #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] == '\0') {
               fprintf(stderr, "%s <owner> <file>\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

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