SSH¶

Converting SSH2 Keys¶

From ssh2 to openssh

ssh-keygen -i -f id_dsa.pub > id_dsa_open.pub

From OpenSSH to ssh2

ssh-keygen -e -f id_dsa.pub > id_dsa_ssh2.pub

SCP Speed UP¶

To increase speed on transfer you can force cipher to arcfour.
You can use same mechanism with rsync when you use ssh encapsulation.

scp -c arcfour <source> <destination>

rsync -av -e "ssh -c arcfour -l <username>" <Source> <Destination>

NOTE: THis reduce your security though

SSH Tunnels¶

Forward Tunnel¶

It is used when you want to forward local port to remote port over SSH.

ssh -f -N -L 5445:localhost:5432 root@<machine>

Reverse Tunnel¶

It is used when you want to forward Remote Port to Local Port.
Usually used to allow access other way around.

ssh -f -N -R 5445:localhost:5432 root@<machine>

SSH Agent automation¶

Undefine existing value and define new value in session.
This also keep the value same since nothing is changing.

File: .screenrc

    unsetenv SSH_AUTH_SOCK
    setenv SSH_AUTH_SOCK $HOME/.screen/ssh-auth-sock.$USERNAME

Each call of screen command will overwrite the existing symlink.

File: .bashrc

    _ssh_auth_save() {
            ln -sf "$SSH_AUTH_SOCK" "$HOME/.screen/ssh-auth-sock.$USERNAME"
    }
    alias screen='_ssh_auth_save ; screen'

Now add key to your session with "ssh-add".
That should do it.

Tips & Tricks¶

Show fingerprint of key¶

Important: You can use -v to print random ASCII Image

# Using -E can specify MD5 has which mostly require to compare
ssh-keygen -lf .ssh/OLD/id_rsa.pub.old

OR

ssh-keygen -l -F ip.k2patel.in

It will print for all public key in single file if there is multiple key in it.
Also, it is usefull in identifying MITM Attack by comparing against your known host.

You can enabled printing of server key by setting following variable.

Tip: you can setup on any of following file /etc/ssh/ssh_config OR .ssh/config
VisualHostKey yes

Run Command from file Remotely¶

Place all your command in xyz file. And run as follows

ssh -l k2patel nice.k2patel.in "`cat xzy`"

Comment on public key¶

You can control comment on public key during generation using following command.

ssh-keygen -t rsa -C "k2patel rsync to remote server xyz" -f .ssh/remote_xyz

Temporarily disable ssh key forwarding¶

This will disable key forwarding, while login with the key.

ssh yahoo.com -i .ssh/id_ed25519 -o IdentitiesOnly=yes -F /dev/null -l ketan