Ssh – killing a process on a remote machine when the machine is stuck

You can also use ssh to configure password-less login to a remote computer.

It is just (on computer a):

$ ssh-keygen # use an empty password!
$ scp ~/.ssh/id_rsa.pub computer_b:.ssh/authorized_keys

That's it.

Now you can do a

$ ssh computer_b

without having to enter a password.

You can optionally configure things like:

• host alias for computer_b, e.g. to be able to enter ssh alias
• set public-key authentication as default for that host/alias
• allow only public-key authentication (for the sshd on computer_b)

Unless you can't use ssh, it seems to be much more convenient to setup than rlogin.

Plus, ssh protects you against main-in-the-middle attacks and eavesdropping.

Troubleshooting

Make sure that the ~/.ssh has the right permissions (on both systems) - i.e. is only accessible by your user - otherwise ssh ignores it. That means only rwx------ for the directory and rw------- for the files. Use ls -l and ls -ld to verify this.

Make sure that the remote ~/.ssh/authorized_keys contains the correct public key. Verify via:

$ ssh computer_b cat '~/.ssh/authorized_keys' # remote
$ cat ~/.ssh/id_rsa.pub # local

If the setup does not work like this, perhaps you have to explicitly configure the client side, i.e. adding something like this to .ssh/config:

Host computer_b
Hostname some_hostname
User juser
PreferredAuthentications publickey # makes testing easier
IdentitiesOnly yes
IdentityFile ~/.ssh/id_rsa.pub

For diagnosing issues it is also useful to add -v to ssh call, e.g.:

$ ssh -v computer_b

From AS try: ssh root@PC -L 12001:WS:22

and then (still from AS - probably another session): ssh root@localhost -p 12001 and it will be tunneled to WS to port 22.