• ssh is a program for logging securely into a remote machine and for executing commands on a remote machine
  • More precisely ssh is an SSH client using the SSH protocol

• We assume below that you have a my_login account on the remote remote_server computer, and you know your password
  • This page will also show some examples using the LSCE and IPSL (ciclad) servers

• Instead of a password, you can also use a set of private and public keys and a passphrase

• Many programs are said to work over ssh when they implicitly use the ssh protocol to securely transfer their data from one server to another: scp (copy remote directories and files), rsync (synchronize remote directories and files), …

• Some history: before you were born, and the world and internet were a safer place, people used less secure programs like telnet, rlogin, rsh, ftp, …

• ssh [options] [my_login@]remote_server
  • If your login is the same on the local and remote computer, you can omit the optional my_login@: e.g. just use ssh ssh1.lsce.ipsl.fr

• Most common options:
  • -X: Enable X11 forwarding. This option will allow you to start graphical programs on the remote server
    • If -X does not work, use -Y instead (Enable trusted X11 forwarding)
    • Using this option will automatically define the DISPLAY environment variable that is required by graphical programs. Otherwise, DISPLAY will not be defined
      

      jypeter@lsce5203:~$ echo $DISPLAY
      localhost:0.0
      jypeter@lsce5203:~$ ssh ssh1.lsce.ipsl.fr
      Last login: Wed Jul  8 14:45:31 2020 from 176-142-31-75.abo.bbox.fr
      [jypeter@ssh1 ~]$ echo $DISPLAY
      DISPLAY: Undefined variable.
      [jypeter@ssh1 ~]$ logout
      Connection to ssh1.lsce.ipsl.fr closed.
      jypeter@lsce5203:~$ ssh -X ssh1.lsce.ipsl.fr
      [jypeter@ssh1 ~]$ echo $DISPLAY
      localhost:43.0

    • In order to display graphical windows, you also need to have a local X server running!
      • Windows: install, configure and launch VcXsrv
  • -A: enable agent forwarding. This is useful when you use ssh keys, and an ssh agent
  • -t command: this option allows you to execute a command on the remote server (without displaying the output of the initial ssh). We use it mostly to chain ssh connections, when we have to go through a specific server to access another one
    e.g.
  • -v: verbose mode. Use this only option when you can't connect, or things don't seem to work correctly. Analyzing the verbose output when you start ssh should allow you, or the system administrators, to find out what is wrong

aliases

.ssh/

• If you want to know more (options, etc…), check the man(ual) page on Linux: man ssh
• emacs

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