Linux – SSH via 3rd Machine

linuxsshssh-tunnel

Local Computer (Fedora)  --SSH-->  Server1  --SSH-->  Server2

In some environments I work in, we have to use "jump boxes" where you ssh to one server in order to get to another server. Is there a quick way to do this, perhaps by editing ~/.ssh/config, such that whenever I ssh to Server2 from my local computer, it automatically creates the necessary connection to Server1? I can setup keys so that I'm not prompted for a password to Server1 if necessary.

Best Answer

This type of functionality was added into OpenSSH version 5.4 and can be used by doing

ssh -W server2 server1

Where server2 is your intended destination and server1 is your proxy host. You can make this easier by using the ProxyCommand option in your ssh config, something like:

host = *.example.com
user = packs
port = 22
ProxyCommand ssh -W %h:%p server1

I've also seen it done using netcat, so with the same examples as above

ssh server1 nc -q0 server2 22

Similarly, this can also be used in your ssh config, except replacing the ProxyCommand as

ProxyCommand ssh server1 nc -q0 %h %p

Related Solutions

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

SSH – Bad Owner or Permissions on ~/.ssh/config

I needed to have rw for user only permissions on config. This fixed it.

chmod 600 ~/.ssh/config

As others have noted below, it could be the file owner. (upvote them!)

chown $USER ~/.ssh/config

If your whole folder has invalid permissions here's a table of possible permissions:

Path	Permission
.ssh directory (code)	0700 (drwx------)
private keys (ex: `id_rsa`) (code)	0600 (-rw-------)
`config`	0600 (-rw-------)
public keys (*.pub ex: `id_rsa.pub`)	0644 (-rw-r--r--)
`authorized_keys` (code)	0644 (-rw-r--r--)
`known_hosts`	0644 (-rw-r--r--)

Sources:

openssh check-perm.c
openssh readconf.c
openssh ssh_user_config fix_authorized_keys_perms

Best Answer

Related Solutions

Ssh – How to automate SSH login with password

SSH – Bad Owner or Permissions on ~/.ssh/config

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