View source for SSH

=Display key fingerprints informations in /var/log/auth.log=
If you have multiple users connecting to a single SSH account (ie: root) and you want to identify clearly who's connecting:

Ensure this value in /etc/ssh/sshd_config:
 LogLevel VERBOSE

<syntaxhighlight lang="bash">
/etc/init.d/ssh restart
</syntaxhighlight>

Everytime a new SSH connexion is completed you could list the fingerprint used: tail -f /var/log/auth.log

=To identify a fingerprint's owner by listing all entries in /root/.ssh/authorized_keys=

<syntaxhighlight lang="bash">
while read l; do
  [[ -n $l && ${l###} = $l ]] && ssh-keygen -l -f /dev/stdin <<<$l;
done < /root/.ssh/authorized_keys
</syntaxhighlight>

=To disable SSH host key checking=
<syntaxhighlight lang="bash">
for i in 172.16.1.{1..12} 172.17.1.{1..10} 172.18.1.{1..3}; do scp -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no /etc/scribe/scribe.conf root@$i:/etc/scribe/scribe.conf; done
</syntaxhighlight>

=Improve copy performance by changing Cipher=
<syntaxhighlight lang="bash">
scp -o Cipher=arcfour local-file user@remote.example.com:/path/
</syntaxhighlight>

= Convert OpenSSH keys to .ppk (Putty) on Linux with puttygen =
(Adapt rsa / dsa)

<syntaxhighlight lang="bash">
apt-get install putty-tools
cd ~/.ssh/
puttygen id_dsa -o id_dsa.ppk
</syntaxhighlight>

= Enter SSH Passphrase only once =
If you want to prevent to be asked for your passphrase everytime you try a SSH connection with this message:

<i>Enter passphrase for key '/home/username/.ssh/id_rsa'</i>

Add in your .ssh/config one line at the beginning:

 AddKeysToAgent yes


= Deprecated options when restarting OpenSSH in Debian Stretch (Ex: Deprecated option KeyRegenerationInterval) =

You can remove deprecated configuration lines with this:

<syntaxhighlight lang="bash">
sed -i '/KeyRegenerationInterval/d' /etc/ssh/sshd_config
sed -i '/ServerKeyBits/d' /etc/ssh/sshd_config
sed -i '/RSAAuthentication/d' /etc/ssh/sshd_config
sed -i '/RhostsRSAAuthentication/d' /etc/ssh/sshd_config

/etc/init.d/ssh restart
</syntaxhighlight>