Single or Numbered Backups

When Emacs makes a backup file, its name is normally constructed by appending ‘~’ to the file name being edited; thus, the backup file for eval.c would be eval.c~.

If access control stops Emacs from writing backup files under the usual names, it writes the backup file as ~/.emacs.d/%backup%~. Only one such file can exist, so only the most recently made such backup is available.

Emacs can also make numbered backup files. Numbered backup file names contain ‘.~’, the number, and another ‘~’ after the original file name. Thus, the backup files of eval.c would be called eval.c.~1~, eval.c.~2~, and so on, all the way through names like eval.c.~259~ and beyond.

The variable version-control determines whether to make single backup files or multiple numbered backup files. Its possible values are:


Make numbered backups for files that have numbered backups already. Otherwise, make single backups. This is the default.


Make numbered backups.


Never make numbered backups; always make single backups.

The usual way to set this variable is globally, through your init file or the customization buffer. However, you can set version-control locally in an individual buffer to control the making of backups for that buffer’s file (see Local Variables). Some modes, such as Rmail mode, set this variable. You can also have Emacs set version-control locally whenever you visit a given file (see Local Variables in Files).

If you set the environment variable VERSION_CONTROL, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable version-control accordingly at startup. If the environment variable’s value is ‘t’ or ‘numbered’, then version-control becomes t; if the value is ‘nil’ or ‘existing’, then version-control becomes nil; if it is ‘never’ or ‘simple’, then version-control becomes never.

If you set the variable make-backup-file-name-function to a suitable Lisp function, you can override the usual way Emacs constructs backup file names.