23.8.2 Version Control and the Mode Line

When you visit a file that is under version control, Emacs indicates this on the mode line. For example, ‘RCS-1.3’ says that RCS is used for that file, and the current version is 1.3.

The character between the back-end name and the version number indicates the version control status of the file. ‘-’ means that the work file is not locked (if locking is in use), or not modified (if locking is not in use). ‘:’ indicates that the file is locked, or that it is modified. If the file is locked by some other user (for instance, ‘jim’), that is displayed as ‘RCS:jim:1.3’.

When Auto Revert mode (see section Reverting a Buffer) reverts a buffer that is under version control, it updates the version control information in the mode line. However, Auto Revert mode may not properly update this information if the version control status changes without changes to the work file, from outside the current Emacs session. If you set auto-revert-check-vc-info to t, Auto Revert mode updates the version control status information every auto-revert-interval seconds, even if the work file itself is unchanged. The resulting CPU usage depends on the version control system, but is usually not excessive.