`ssh` configuration

ssh configuration

ubuntu ssh


The default ssh configuration shipped with your GNU/Linux distribution may not be ideal. Here are some tweaks I use:

Idle connection

The remote ssh server (or a router/firewall in-between) may disconnect an idle connection. To prevent that, it’s possible to send keep-alive from the client site, by editing /etc/ssh/ssh_config or ~/ssh/config:

Host *
ServerAliveInterval 240

or from the server side by editing /etc/ssh/sshd_config

ClientAliveInterval 60

known_host and changing IP

IP addresses may be re-used on some networks, and storing the server fingerprint with the IP address can be disabled.

Host *
CheckHostIP no


Using your local locale on a remote system may not be desirable, the remote host may try to use your a non existent locale and display a lot of warnings, for instance:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
 LANGUAGE = "en_US:en",
 LC_ALL = (unset),
 LC_TIME = "de_CH.UTF-8",
 LC_ADDRESS = "de_CH.UTF-8",
 LC_NAME = "de_CH.UTF-8",
 LC_NUMERIC = "de_CH.UTF-8",
 LC_PAPER = "de_CH.UTF-8",
 LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").
locale: Cannot set LC_ALL to default locale: No such file or directory

To prevent your host from sending the locale edit /etc/ssh/ssh_config (or your user’s ~/.ssh/config) and and remove LANG and LC_* from the sent variables :

#SendEnv LANG LC_*

To prevent the remote machine form accepting the locale edit /etc/ssh/sshd_config (dont’ forget the d) and remove LANG and LC_* from the accepted environment variable:

#AcceptEnv LANG LC_*


Question, remark, bug? Don't hesitate to contact me or report a bug.