CHOWN

chown, fchown, lchown ? change ownership of a file

#include <sys/types.h>
#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);

The owner of the file specified by path or by fd is changed. Only the super-user 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. The super-user 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-super-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 behaviour 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.

On success, zero is returned. On error, ?1 is returned, and errno is set appropriately.

Depending on the file system, other errors can be returned. The more general errors for chown are listed below:

EPERM

The effective UID does not match the owner of the file, and is not zero; or the owner or group were specified incorrectly.

EROFS

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

EFAULT

path points outside your accessible address space.

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.

EACCES

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

ELOOP

Too many symbolic links were encountered in resolving path.

The general errors for fchown are listed below:

EBADF

The descriptor is not valid.

ENOENT

See above.

EPERM

See above.

EROFS

See above.

EIO

A low-level I/O error occurred while modifying the inode.

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 prototype for fchown is only available if __USE_BSD is defined.

The chown call conforms to SVr4, SVID, POSIX, X/OPEN. The 4.4BSD version can only be used by the superuser (that is, ordinary users cannot give away files). SVr4 documents EINVAL, EINTR, ENOLINK and EMULTIHOP returns, but no ENOMEM. POSIX.1 does not document ENOMEM or ELOOP error conditions.

The fchown call conforms to 4.4BSD and SVr4. SVr4 documents additional EINVAL, EIO, EINTR, and ENOLINK error conditions.

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.

chmod(2), flock(2)