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tramp: Auto-save and Backup

 
 4.18 Auto-save and Backup configuration
 =======================================
 
 To avoid TRAMP from saving backup files owned by root to locations
 accessible to others, default backup settings in
 ‘backup-directory-alist’ have to be altered.
 
    Here’s a scenario where files could be inadvertently exposed.  Emacs
 by default writes backup files to the same directory as the original
 files unless changed to another location, such as ‘~/.emacs.d/backups/’.
 Such a directory will also be used by default by TRAMP when using, say,
 a restricted file ‘/su:root@localhost:/etc/secretfile’.  The backup file
 of the secretfile is now owned by the user logged in from tramp and not
 root.
 
    When ‘backup-directory-alist’ is ‘nil’ (the default), such problems
 do not occur.
 
    To “turn off” the backup feature for TRAMP files and stop TRAMP from
 saving to the backup directory, use this:
 
      (add-to-list 'backup-directory-alist
                   (cons tramp-file-name-regexp nil))
 
 Disabling backups can be targeted to just the ‘su’ and ‘sudo’ methods:
 
      (setq backup-enable-predicate
            (lambda (name)
              (and (normal-backup-enable-predicate name)
                   (not
                    (let ((method (file-remote-p name 'method)))
                      (when (stringp method)
                        (member method '("su" "sudo"))))))))
 
    Another option is to create better backup file naming with user and
 host names prefixed to the file name.  For example, transforming
 ‘/etc/secretfile’ to
 ‘~/.emacs.d/backups/!su:root@localhost:!etc!secretfile’, set the TRAMP
 variable ‘tramp-backup-directory-alist’ from the existing variable
 ‘backup-directory-alist’.
 
    Then TRAMP backs up to a file name that is transformed with a prefix
 consisting of the DIRECTORY name.  This file name prefixing happens only
 when the DIRECTORY is an absolute local file name.
 
 Example:
 
      (add-to-list 'backup-directory-alist
                   (cons "." "~/.emacs.d/backups/"))
      (setq tramp-backup-directory-alist backup-directory-alist)
 
 The backup file name of ‘/su:root@localhost:/etc/secretfile’ would be
 ‘/su:root@localhost:~/.emacs.d/backups/!su:root@localhost:!etc!secretfile~’
 
    Just as for backup files, similar issues of file naming affect
 auto-saving TRAMP files.  Auto-saved files are saved in the directory
 specified by the variable ‘auto-save-file-name-transforms’.  By default
 this is set to the local temporary directory.  But in some versions of
 Debian GNU/Linux, this points to the source directory where the Emacs
 was compiled.  Reset such values to a valid directory.
 
    Set ‘auto-save-file-name-transforms’ to ‘nil’ to save auto-saved
 files to the same directory as the original file.
 
    Alternatively, set the variable ‘tramp-auto-save-directory’ to direct
 all auto saves to that location.
 

Info Catalog tramp: Android shell setup tramp: Configuration tramp: Windows setup hints