About SSH

SSH uses public-key cryptography to authenticate the remote computer and allow the remote computer to authenticate the user, if necessary.

SSH is typically used to log into a remote machine and execute commands, but it also supports tunneling, forwarding arbitrary TCP ports and X11 connections. SSH uses a client-server protocol.

SSH uses private/public key pairs to log into another host. Users no longer have to supply a password every time they log on to a remote host.

SSH is used when running any of the following:

Remote log on to a lightly loaded host (lslogin)
An interactive job (bsub -IS | -ISp | ISs)
An interactive X-window job with X11 forwarding (bsub -XF)
An interactive X-window job, without X11 forwarding (bsub -IX)
An externally submitted job (esub)

X-Window job options

Depending on your requirements for X-Window jobs, you can choose either bsub -XF (recommended) or bsub -IX. Both options encrypt the X-Server and X-Clients.

Mode	Benefits	Drawbacks
bsub -XF (X11 forwarding): Recommended	Any password required can be typed in when needed. Does not require the X-Server host to have the SSH daemon installed.	The user must enable X11 forwarding in the client. Submission and execution hosts must be UNIX.
bsub -IX (interactive X-window)	The execution host contacts the X-Server host directly (no user steps required). Hosts can be any OS that OpenSSH supports.	Requires the SSH daemon installed on the X-Server host. Must use private keys with no passwords set.

Scope

Table 1. SSH X11 forwarding (-XF)
Applicability	Details
Dependencies	OpenSSH 3.9p1 and up is supported. OpenSSL 0.9.7a and up is supported. You must have SSH correctly installed on all hosts in the cluster. You must use an SSH client to log on to the submission host from the display host. You must install and run the X-Server program on the display host.
Operating system	Only UNIX for submission and execution hosts. The display host can be any operating system.
Limitations	You cannot run with bsub -K, -IX, or -r. You cannot bmod a job submitted with X11 forwarding. Cannot be used with job arrays, job chunks, or user account mapping. Jobs submitted with X11 forwarding cannot be checked or modified by esubs. Can only run on UNIX hosts (submission and execution hosts).

Table 2. Interactive X-window without X11 forwarding (-IX)
Applicability	Details
Dependencies	You must have OpenSSH correctly installed on all hosts in the cluster. You must generate public/private key pairs and add the content of the public key to the authorized_keys file on remote hosts. For more information, refer to your SSH documentation. For X-window jobs: You must set the DISPLAY environment variable to `X-serverHost`:0.0, where `X-serverHost` is the name of the X-window server. Ensure that the X-server can access itself. Run, for example, xhost +localhost.
Operating system	Any OS that also supports OpenSSH.
Limitations	Cannot be used with job arrays or job chunks. Private user keys must have no password set. You cannot run with -K , -r, or -XF.