CHOWN(2) System Calls Manual CHOWN(2)

chown, fchown, lchown, fchownatchange owner and group of a file

#include <unistd.h>

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

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

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

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

The owner ID and group ID of the file named by path or referenced by fildes 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.

The () system call clears the set-user-id and set-group-id bits on the file. The chown() system call follows symbolic links to operate on the target of the link rather than the link itself.

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

The () system call is similar to chown() but does not follow symbolic links.

The () system call is equivalent to the chown() and lchown() except in the case where path specifies a relative path. In this case the file to be changed is determined relative to the directory associated with the file descriptor fd instead of the current working directory.

Values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

If path names a symbolic link, ownership of the symbolic link is changed.
If path names a symbolic link, ownership of the symbolic link is changed. If any any other symbolic link is encountered it is not followed and an error is returned instead.

If () is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to chown() or lchown() respectively, depending on whether or not the AT_SYMLINK_NOFOLLOW bit is set in the flag argument.

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

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The chown() and lchown() system calls will fail if:

[]
Search permission is denied for a component of the path prefix.
[]
The path argument points outside the process's allocated address space.
[]
Too many symbolic links are encountered in translating the pathname. This is taken to be indicative of a looping symbolic link.
[]
If AT_SYMLINK_NOFOLLOW_ANY is passed a symbolic link was encountered in translating the pathname.
[]
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[]
A component of path does not exist.
[]
A component of the path prefix is not a directory.

The fchown() system call will fail if:

[]
The fildes argument does not refer to a valid descriptor.
[]
The fildes argument refers to a socket, not a file.

Any of these calls will fail if:

[]
Its execution is interrupted by a signal.
[]
An I/O error occurs while reading from or writing to the file system.
[]
The effective user ID does not match the owner of the file and the calling process does not have appropriate (i.e., root) privileges.
[]
The named file resides on a read-only file system.

In addition to the errors specified for chown() and lchown(), the fchownat() system call may fail if:

[]
The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for searching.
[]
The value of the flag argument is not valid.
[]
The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

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

The chown() system call is expected to conform to IEEE Std 1003.1-1990 (“POSIX.1”). The fchownat() system call is expected to conform to POSIX.1-2008 .

The chown() function appeared in Version 7 AT&T UNIX. The fchown() system call appeared in 4.2BSD.

The chown() and fchown() system calls were changed to follow symbolic links in 4.4BSD. The lchown() system call was added in FreeBSD 3.0 to compensate for the loss of functionality.

The fchownat() system call appeared in OS X 10.10

April 19, 1994 macOS 14.4