Tribblix: manual page: chown.2

CHOWN(2) System Calls CHOWN(2)

NAME

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

SYNOPSIS

#include <unistd.h>
#include <sys/types.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 fildes, uid_t owner, gid_t group);

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

DESCRIPTION

The chown() and fchown() functions set the owner ID and group ID of the
file specified by path or referenced by the open file descriptor fildes
to owner and group respectively. If owner or group is specified as -1,
chown() and fchown() do not change the corresponding ID of the file.

The lchown() function sets the owner ID and group ID of the named file
in the same manner as chown(), unless the named file is a symbolic
link. In this case, lchown() changes the ownership of the symbolic
link file itself, while chown() changes the ownership of the file or
directory to which the symbolic link refers.

The fchownat() function sets the owner ID and group ID of the named
file in the same manner as chown(). If, however, the path argument is
relative (does not start with a "/"), the path is resolved relative to
the fildes argument rather than the current working directory. If the
fildes argument has the special value AT_FDCWD, the path resolution
reverts back to current working directory relative. If the flag
argument is set to AT_SYMLINK_NOFOLLOW, the function behaves like
lchown() with respect to symbolic links. If the path argument is
absolute, the fildes argument is ignored. If the path argument is a
null pointer, the function behaves like fchown().

If chown(), lchown(), fchown(), or fchownat() is invoked by a process
that does not have {PRIV_FILE_SETID} asserted in its effective set, the
set-user-ID and set-group-ID bits of the file mode, S_ISUID and S_ISGID
respectively, are cleared (see chmod(2)). Additional restrictions
apply when changing the ownership to uid 0.

The operating system defines several privileges to override
restrictions on the chown() family of functions. When the
{PRIV_FILE_CHOWN} privilege is asserted in the effective set of the
current process, there are no restrictions except in the special
circumstances of changing ownership to or from uid 0. When the
{PRIV_FILE_CHOWN_SELF} privilege is asserted, ownership changes are
restricted to the files of which the ownership matches the effective
user ID of the current process. If neither privilege is asserted in
the effective set of the calling process, ownership changes are limited
to changes of the group of the file to the list of supplementary group
IDs and the effective group ID.

The operating system provides a configuration option,
{_POSIX_CHOWN_RESTRICTED}, to control the default behavior of processes
and the behavior of the NFS server. If {B_POSIX_CHOWN_RESTRICTED} is
not in effect, the privilege {PRIV_FILE_CHOWN_SELF} is asserted in the
inheritable set of all processes unless overridden by policy.conf(5) or
user_attr(5). To set this configuration option, include the following
line in /etc/system:

set rstchown = 1

To disable this option, include the following line in /etc/system:

set rstchown = 0

See system(5) and fpathconf(2).

Upon successful completion, chown(), fchown(), lchown(), and fchownat()
mark for update the st_ctime field of the file.

RETURN VALUES

Upon successful completion, 0 is returned. Otherwise, -1 is returned,
the owner and group of the named file remain unchanged, and errno is
set to indicate the error.

ERRORS

All of these functions will fail if:

EPERM The effective user ID does not match the owner of
the file and the {PRIV_FILE_CHOWN} privilege is not
asserted in the effective set of the calling
process, or the {PRIV_FILE_CHOWN_SELF} privilege is
not asserted in the effective set of the calling
process.

The chown(), lchown(), and fchownat() functions will fail if:

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

EFAULT The path argument points to an illegal address and
for fchownat(), the file descriptor has the value
AT_FDCWD.

EINTR A signal was caught during the execution of the
chown() or lchown() function.

EINVAL The group or owner argument is out of range.

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

ELOOP Too many symbolic links were encountered in
translating path.

ENAMETOOLONG The length of the path argument exceeds {PATH_MAX},
or the length of a path component exceeds {NAME_MAX}
while {_POSIX_NO_TRUNC} is in effect.

ENOLINK The path argument points to a remote machine and the
link to that machine is no longer active.

ENOENT Either a component of the path prefix or the file
referred to by path does not exist or is a null
pathname.

ENOTDIR A component of the path prefix of path is not a
directory, or the path supplied to fchownat() is
relative and the file descriptor provided does not
refer to a valid directory.

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

The chown() and fchownat() functions will fail if:

EBADF For fchown(), the fildes argument is not an open
file descriptor.

For fchownat(), the path argument is not absolute
and the fildes argument is neither AT_FDCWD, nor an
open file descriptor.

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

EINTR A signal was caught during execution of the
function.

ENOLINK The fildes argument points to a remote machine and
the link to that machine is no longer active.

EINVAL The group or owner argument is out of range.

EROFS The named file referred to by fildes resides on a
read-only file system.

INTERFACE STABILITY