It is possible to automatically login in a ssh session on a remote system. To make this possible ssh keys needs to be exchanges between the client and target. For more information see also: http://backuppc.sourceforge.net/faq/ssh.html#why_do_i_need_ssh. You can do this for any user on the target system. The example below assumes loging in as root user on the target system.

As root on the target machine, use ssh-keygen to generate a public/private key pair:

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

As a password, you would type nothing (just enter). This will save the public key in /root/.ssh/id_rsa.pub and the private key in /root/.ssh/id_rsa, if you don't specify another location.

This might not be necessary if the client key has already be created for other targets, so you can reuse it. Repeat the above steps for the user 'oscar' on the client that will execute the ssh. Login as user on the client and perform the following steps:

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

After this the file ~/.ssh/id_rsa.pub should exist in the .ssh in the home directory of user 'oscar'. Make a copy of the public key to make it recognizable.

To allow the client to ssh to the target system as root, you need to place the client's public key into root's authorized list on the target system. There are 2 different ways to achieve this:

• Manual
• With 'ssh-copy-id'

Append client's public key (BackupPC_id_rsa.pub) to root's /root/.ssh/authorized_keys2 file on the client:

 Get the public key from the backuppc server:
 # cd /root/.ssh
 # scp backuppc@192.168.xx.xx:/media/raid/backuppc/.ssh/id_rsa.pub  BackupPC_id_rsa.pub
 # touch ~/.ssh/authorized_keys2
 # cat BackupPC_id_rsa.pub >> ~/.ssh/authorized_keys2
 # rm BackupPC_id_rsa.pub

You need to place the client's public key into backuppc's ~/.ssh/known_hosts file, otherwise you will get a “Host key verification failed.” error, and backuppc will not be able to log into the client. To place the client key into the ~/.ssh/known_hosts file, you need to do this (make sure ~/.ssh/client_id_rsa.pub is the client's public key, which needs to be copied from the client):

  backuppc@backupserver scp root@192.168.xx.xx:/root/.ssh/id_rsa.pub Client-key.pub
  backuppc@backupserver touch ~/.ssh/known_hosts
  backuppc@backupserver cat ~/.ssh/Client-key.pub >> ~/.ssh/known_hosts
  backuppc@backupserver rm Client-key.pub

Or symply try to ssh from backuppc to client as root. The key will be placed automatically in known_hosts:

  backuppc@backupserver ssh root@192.168.xx.xx

Copy your keys to the target system:

$ ssh-copy-id remoteusername@targetsystem

remoteusername@targetsystem's password: 

Now try logging into the machine, with ssh 'remoteusername@targetsystem'. The key of your system should now be place in to the .ssh subdirectory in the home directory of remoteusername on the target system.

/home/remoteusername/.ssh/authorized_keys

or

/root/.ssh/authorized_keys

or on openwrt:

/etc/dropbear/authorized_keys

This should now work from the server to the client:

  backuppc@backupserver ssh root@192.168.xx.xx