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### 4.13 Reusing connection related information.

In order to reduce initial connection time, tramp stores connection related information persistently. The variable `tramp-persistency-file-name` keeps the file name where these information are written. Its default value is `~/.emacs.d/tramp`. It is recommended to choose a local file name.

tramp reads this file during startup, and writes it when exiting GNU Emacs. You can simply remove this file if tramp shall be urged to recompute these information next GNU Emacs startup time.

Using such persistent information can be disabled by setting `tramp-persistency-file-name` to `nil`.

Once consequence of reusing connection related information is that tramp needs to distinguish hosts. If you, for example, run a local `sshd` on port 3001, which tunnels `ssh` to another host, you could access both `/ssh :localhost:` and `/ssh:localhost#3001:`. tramp would use the same host related information (like paths, Perl variants, etc) for both connections, although the information is valid only for one of them.

In order to avoid trouble, you must use another host name for one of the connections, like introducing a `Host` section in `~/.ssh/config` (see Frequently Asked Questions) or applying multiple hops (see Multi-hops).

When tramp detects a changed operating system version on a remote host (via the command `uname -sr`), it flushes all connection related information for this host, and opens the connection, again.