chown and -F formats

username, UID

That user; no group.

username:

That user and the corresponding login group.

{username, UID}:{groupname, GID}

That user and group.

:group, :GID

No user; that group.

In all cases, a user or group name takes precedence over the ID (i.e. if a 1312 user exists, that argument will resolve thereto, rather than UID 1312).

Research UNIX

chown appears in the first edition of the UNIX Programmer's Manual as chown(I):

The owner may be decimal, which takes precedent (if the first character of owner is a digit), or a name as it appeared in /etc/uids (the world-readable companion to /etc/passwd, which "should be updated along with the password file").

Version 3 AT&T UNIX sees encrypt(III)ed passwords in /etc/passwd, hence its world-readability, and, hence, use as the single point of ID look-up. chown(II) unconditionally clears the set-user-ID bit instead of denying the operation if it's set.

Version 4 AT&T UNIX preserves it if done by root or real ID of the new owner — i.e. if chown is invoked by the new owner (possibly transitively) set-user-ID current owner.

Version 5 AT&T UNIX only persists the set-user-ID bit for root.

Version 6 AT&T UNIX says it forbids ownership changes to anyone but root "in order to simplify as yet unimplemented accounting procedures", and, hence, moves the manual to section VIII. But doesn't actually do it, and the owner can still give away files. The set-user-ID is no longer cleared, either. chgrp(VIII) appears for the first time as well, with identical restrictions and manual page, drawing upon /etc/group.

Version 7 AT&T UNIX keeps up the lie and merges the manuals into a common chown(1).

The BSD

3BSD sees an off-by-default (and otherwise undocumented) -DERNIE kernel macro, controlling clearing of set-user- and -group-ID bits. 4BSD moves the page back to section 8, executables to /etc, and replaces previous macros with a strictly controlled and documented list, among which INSECURE, off-by-default, enables "old style non-vanishing suid bits" — in a default configuration, both bits are cleared.

4.2BSD sees

4.3BSD sees

4.3BSD-Tahoe chown supports, though undocumented, .group and owner. forms, both setting only the specified arguments.

4.3BSD-Reno moves chown to the familiar /usr/sbin, with the appropriate SYNOPSIS change, and chgrp to /usr/bin.

Changing the owner is only allowed for root, and changing the group is also allowed if the caller is a member — as present-day. If the owner (group) was changed by not root, the appropriate set-user- or -group-ID bit is cleared.

4.4BSD sees

User and group names are given precedence over IDs, for compatibility with IEEE Std 1003.2 (“POSIX.2”). Symlink ownership is unchangeable as a system limitation, making these operations effectively successful no-ops thereon.

4.4BSD-Lite2 Sees [-HRfh] replaced with [-R [-H -| -L -| -P]] [-f], as present-day. Symbolic links have lost owners entirely.

System V

Sees Version 7 AT&T UNIX chown and chgrp, except with set-user- and -group-ID clearing for non-root, until AT&T System V Release 3 UNIX, which validates numeric IDs to be ushorts (16-bit), rather than blindly passing through ints from atoi(3) — 16 bits on the PDP-11, but 32 bits on the 3B2.

AT&T System V Release 4 UNIX sees

A recurring comment in the filesystems' *setattr() functions notes:

/*
 * Change file ownership; must be the owner of the file
 * or the super-user.  If the system was configured with
 * the "rstchown" option, the owner is not permitted to
 * give away the file, and can change the group id only
 * to a group of which he or she is a member.
 */

Standards

X/Open Portability Guide Issue 2 (“XPG2”) describes chown and chgrp as they're found in AT&T UNIX, permitting any sort of restriction, but outlining that "some systems" permit ⟨root and owner⟩, ⟨just root⟩, or ⟨root and owner (if in groups)⟩ limitations. The name/ID precedence is unspecified except for hinted at with "The owner may be either a decimal user ID or a login name found in the User Database", and likewise for the group.

IEEE Std 1003.2-1992 (“POSIX.2”) sees

The : separator is a refinement of the 4.3BSD . syntax, since users and groups are allowed to have names that contain "."s, but no systems support ones with ":"s.

IEEE Std 1003.1-2001 (“POSIX.1”) adds -h and -PHL, as present-day.