NAME

chown, lchown, fchown, fchownat — change owner and group of a file

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>

int
chown(const char *path, uid_t owner, gid_t group);

int
lchown(const char *path, uid_t owner, gid_t group);

int
fchown(int fd, uid_t owner, gid_t group);

#include <fcntl.h>

int
fchownat(int fd, const char *path, uid_t owner, gid_t group, int flag);

DESCRIPTION

The owner ID and group ID of the file named by path or referenced by fd is changed as specified by the arguments owner and group. The owner of a file may change the group to a group of which he or she is a member, but the change owner capability is restricted to the super-user.

When called to change the owner of a file, chown(), lchown() and fchown() clear the set-user-id (S_ISUID) bit on the file. When a called to change the group of a file, chown(), lchown() and fchown() clear the set-group-id (S_ISGID) bit on the file. These actions are taken to prevent accidental or mischievous creation of set-user-id and set-group-id programs.

lchown() is like chown() except in the case where the named file is a symbolic link, in which case lchown() changes the owner and group of the link, while chown() changes the owner and group of the file the link references.

fchown() is particularly useful when used in conjunction with the file locking primitives (see flock(2)).

fchownat() works the same way as chown() (or lchown() if AT_SYMLINK_NOFOLLOW is set in flag) except if path is relative. In that case, it is looked up from a directory whose file descriptor was passed as fd. Search permission is required on this directory. fd can be set to AT_FDCWD in order to specify the current directory.

One of the owner or group id's may be left unchanged by specifying it as (uid_t)-1 or (gid_t)-1 respectively.

RETURN VALUES

The chown(), lchown(), fchown(), and fchownat() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

chown(), lchown() and fchownat() will fail and the file will be unchanged if:

[EACCES]

Search permission is denied for a component of the path prefix.

[EFAULT]

path points outside the process's allocated address space.

[EIO]

An I/O error occurred while reading from or writing to the file system.

[ELOOP]

Too many symbolic links were encountered in translating the pathname.

[ENAMETOOLONG]

A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.

[ENOENT]

The named file does not exist.

[ENOTDIR]

A component of the path prefix is not a directory.

[EPERM]

The effective user ID is not the super-user.

[EROFS]

The named file resides on a read-only file system.

In addition, fchownat() will fail if:

[EBADF]

path does not specify an absolute path and fd is neither AT_FDCWD nor a valid file descriptor open for reading or searching.

[ENOTDIR]

path is not an absolute path and fd is a file descriptor associated with a non-directory file.

fchown() will fail if:

[EBADF]

fd does not refer to a valid descriptor.

[EINVAL]

fd refers to a socket, not a file.

[EIO]

An I/O error occurred while reading from or writing to the file system.

[EPERM]

The effective user ID is not the super-user.

[EROFS]

The named file resides on a read-only file system.

SEE ALSO

chgrp(1), chmod(2), flock(2), symlink(7), chown(8)

STANDARDS

The chown() function deviates from the semantics defined in IEEE Std 1003.1-1990 (“POSIX.1”), which specifies that, unless the caller is the super-user, both the set-user-id and set-group-id bits on a file shall be cleared, regardless of the file attribute changed. The lchown() and fchown() functions, as defined by X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”), provide the same semantics. fchownat() conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

To retain conformance to these standards, compatibility interfaces are provided by the POSIX Compatibility Library (libposix, -lposix) as follows:

• The chown() function conforms to IEEE Std 1003.1-1990 (“POSIX.1”) and X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”).
• The lchown() and fchown() functions conform to X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”).

HISTORY

The fchown() function call appeared in 4.2BSD.

The chown() and fchown() functions were changed to follow symbolic links in 4.4BSD. The lchown() function call appeared in NetBSD 1.3.