Good SSH tips

SSH Tips

1) COPY SSH KEYS TO USER@HOST TO ENABLE PASSWORD-LESS SSH LOGINS. (NOT ON MAC)

ssh-copy-id user@host

To generate the keys use the command ssh-keygen

2) START A TUNNEL FROM SOME MACHINE’S PORT 80 TO YOUR LOCAL POST 2001

ssh -N -L2001:localhost:80 somemachine

Now you can acces the website by going to http://localhost:2001/

3) MOUNT FOLDER/FILESYSTEM THROUGH SSH

sshfs name@server:/path/to/folder /path/to/mount/point

Install SSHFS from http://fuse.sourceforge.net/sshfs.html
Will allow you to mount a folder security over a network.

4) SSH CONNECTION THROUGH HOST IN THE MIDDLE

ssh -t reachable_host ssh unreachable_host

Unreachable_host is unavailable from local network, but it’s available from reachable_host’s network. This command creates a connection to unreachable_host through “hidden” connection to reachable_host.

5) COPY FROM HOST1 TO HOST2, THROUGH YOUR HOST

ssh root@host1 “cd /somedir/tocopy/ && tar -cf – .” | ssh root@host2 “cd /samedir/tocopyto/ && tar -xf -”
Good if only you have access to host1 and host2, but they have no access to your host (so ncat won’t work) and they have no direct access to each other.


6) CREATE A PERSISTENT CONNECTION TO A MACHINE

ssh -MNf <user>@<host>

Create a persistent SSH connection to the host in the background. Combine this with settings in your ~/.ssh/config:
Host host
ControlPath ~/.ssh/master-%r@%h:%p
ControlMaster no
All the SSH connections to the machine will then go through the persisten SSH socket. This is very useful if you are using SSH to synchronize files (using rsync/sftp/cvs/svn) on a regular basis because it won’t create a new socket each time to open an ssh connection.

7) ATTACH SCREEN OVER SSH

ssh -t remote_host screen -r

Directly attach a remote screen session (saves a useless parent bash process)

8) RUN COMPLEX REMOTE SHELL CMDS OVER SSH, WITHOUT ESCAPING QUOTES

ssh host -l user $(<cmd.txt)

Much simpler method. More portable version: ssh host -l user “`cat cmd.txt`”

9) COPY YOUR SSH PUBLIC KEY TO A SERVER FROM A MACHINE THAT DOESN’T HAVE SSH-COPY-ID

cat ~/.ssh/id_rsa.pub | ssh user@machine “mkdir ~/.ssh; cat >> ~/.ssh/authorized_keys”

If you use Mac OS X or some other *nix variant that doesn’t come with ssh-copy-id, this one-liner will allow you to add your public key to a remote machine so you can subsequently ssh to that machine without a password.

10) HOW TO ESTABLISH A REMOTE GNU SCREEN SESSION THAT YOU CAN RE-CONNECT TO

ssh -t [email protected] /usr/bin/screen -xRR

Long before tabbed terminals existed, people have been using Gnu screen to open many shells in a single text terminal. Combined with ssh, it gives you the ability to have many open shells with a single remote connection using the above options. If you detach with “Ctrl-a d” or if the ssh session is accidentally terminated, all processes running in your remote shells remain undisturbed, ready for you to reconnect. Other useful screen commands are “Ctrl-a c” (open new shell) and “Ctrl-a a” (alternate between shells). Read this quick reference for more screen commands: http://aperiodic.net/screen/quick_reference

11) HARDER, FASTER, STRONGER SSH CLIENTS

ssh -4 -C -c blowfish-cbc

We force IPv4, compress the stream, specify the cypher stream to be Blowfish. I suppose you could use aes256-ctr as well for cypher spec. I’m of course leaving out things like master control sessions and such as that may not be available on your shell although that would speed things up as well.

12) TRANSFER SSH PUBLIC KEY TO ANOTHER MACHINE IN ONE STEP

ssh-keygen; ssh-copy-id user@host; ssh user@host

This command sequence allows simple setup of (gasp!) password-less SSH logins. Be careful, as if you already have an SSH keypair in your ~/.ssh directory on the local machine, there is a possibility ssh-keygen may overwrite them. ssh-copy-id copies the public key to the remote host and appends it to the remote account’s ~/.ssh/authorized_keys file. When trying ssh, if you used no passphrase for your key, the remote shell appears soon after invoking ssh user@host.