SSH public-key authentication

Overview

We can use SSH public-key authentication between hosts to enable all sorts of useful functionality, including...

• Password-less login from HostA to HostB
• Ability to execute remote commands from HostA on HostB
• We can automatically administer an entire nework of servers from a central server.

See also: Ansible : Private/Public Keys and SSH Agent setup

Setup

1. Login to HostA as user foo

2. Copy contents of...

   $HOME/.ssh/id_rsa.pub

   If .ssh/id_rsa.pub does not exist, run..

   $ ssh-keygen -t rsa 
   Generating public/private rsa key pair. 
   Enter file in which to save the key (/usr/local/wasuser/.ssh/id_rsa): 
   Enter passphrase (empty for no passphrase): 
   Enter same passphrase again: 
   Your identification has been saved in /usr/local/wasuser/.ssh/id_rsa 
   Your public key has been saved in /usr/local/wasuser/.ssh/id_rsa.pub 
   The key fingerprint is: 
   05:db:12:51:9f:48:dc:43:cd:8f:22:b0:a7:47:2d:17 wasuser@hostname 
   

   Leave passphrase blank.

3. Paste the public key to the remote host (HostB):

   $HOME/.ssh/authorized_keys

   If the directory and/or file do not exist, create them.

4. Set file system permissions...

   chmod go-w $HOME $HOME/.ssh
   chmod 600 $HOME/.ssh/authorized_keys
   chown `whoami` $HOME/.ssh/authorized_keys

5. You can now run commands such as the following on remote host (HostB) from local host (HostA) without being challenged. For example...

   ssh -f HostB mkdir /tmp/MyDir
   scp filename HostB:/tmp/MyDir

To set a passphrase

ssh-keygen -p

Multiple hops

To embed multiple hops of ssh, for example, to execute commands through a Jumpbox:

ssh user@bastionhost "ssh user@themachine.I.need"

rsync example

$ rsync -vprte ssh testfile.txt ihsadm@foo5dc4vl66:/data01/home/ihsadm
building file list ... done
test
sent 75 bytes  received 40 bytes  230.00 bytes/sec
total size is 0  speedup is 0.00

$ rsync -vprte ssh testfile.txt 10.1.84.139:/data01/home/wasuser
building file list ... done
test
sent 75 bytes  received 40 bytes  230.00 bytes/sec
total size is 0  speedup is 0.00

See also

• Port Forwarding (ssh tunnel)