CHOWN(2)

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 the file specified by path or by fd. 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 (with clear S_IXGRP bit) 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
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 arguemnt. 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)