GNU Emacs Manual
M.7.3.1 Basic Version Control with Locking
If locking is used for the file (as with SCCS, and RCS in its default
mode), C-x C-q can either lock a file or check it in:
If the file is not locked, C-x C-q locks it, and
makes it writable so that you can change it.
If the file is locked by you, and contains changes, C-x C-q checks
in the changes. In order to do this, it first reads the log entry
for the new version. See section M.7.3.4 Features of the Log Entry Buffer.
If the file is locked by you, but you have not changed it since you
locked it, C-x C-q releases the lock and makes the file read-only
If the file is locked by some other user, C-x C-q asks you whether
you want to "steal the lock" from that user. If you say yes, the file
becomes locked by you, but a message is sent to the person who had
formerly locked the file, to inform him of what has happened.
These rules also apply when you use CVS in locking mode, except
that there is no such thing as stealing a lock.