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Cluster SSH

Cluster SSH works a little differently from Parallel ssh. Instead of using a single terminal to issue commands to multiple machines, it creates an xterm for each node in the cluster and a controlling window to let you give input for all the nodes in the cluster.

Cluster SSH is available in Ubuntu Hardy Universe, the Fedora 9 repositories, and as a 1-Click install for openSUSE 11. I used the 64-bit package from the Fedora 9 repositories.

You specify one or more machines to connect to on the command line, and Cluster SSH opens a new xterm window for each connection and a single Tk window to let you control Cluster SSH and send input to all the xterm windows at once. The windows generated by running cssh p1 p2, where p1 and p2 are remote machines, is shown in the screenshot below. When it starts up, Cluster SSH will position the xterm windows in a tiled formation for you as shown.

The Cluster SSH File menu lets you see the history of the input you have provided. The history display expands the Cluster SSH window to contain a text area that displays only your input. You can also quit your session from the File menu. Closing the Cluster SSH window will also end the session and close all the xterm windows associated with it.

The Hosts menu lets you Retile Hosts, which repositions your xterms and the main control window in a manner similar to the one used at startup. The Hosts menu also lets you add a new connection to another host to the current session, as well as disable and enable any of the hosts in the current session. The latter option is useful if you are administering a collection of several machines and you want to run a command on all machines except one. For example, you might want to run commands on client machines but when you are playing with iptables rules you might want to exclude the firewall machine temporarily.

Cluster SSH has two machine-wide configuration files, /etc/clusters and /etc/csshrc, which are used to define the machines in a cluster (just a group of hosts you want to connect to) and general settings respectively. You can also have ~/.csshrc as a per-user configuration file. There is no corresponding ~/.clusters file, but you can use the extra_cluster_file configuration directive in your ~/.csshrc file to tell Cluster SSH where to look for your personal version of /etc/clusters.

The clusters file has the form: groupname user1@host1 user2@host2 ... where the usernames are optional. With a clusters file you can simply specify cssh groupname to connect to all the hosts in that group. The below commands show a personal clusters file and a ~/.csshrc file that tells Cluster SSH to use that clusters file. The final line invokes Cluster SSH to connect to the specified hosts as various users.

# cat /root/.cssh-clusters
rougenet p1 ben@p2

# cat /root/.csshrc 
extra_cluster_file = ~/.cssh-clusters

# cssh rougenet

The software defines four hotkeys, which you can rebind to other keys in your csshrc file. Ctrl-q closes the current session, Ctrl-+ lets you add a new host to the current session, Alt-n pastes the remote hostname into each xterm when the main Cluster SSH window is active, and Alt-r retiles the xterm windows. As an example of Alt-n, if you typed echo Alt-n into the CSSH window in the screenshot, the left terminal would show echo vfedora864prx1 in its xterm, and the right terminal would show echo vfedora864prx2. There is no keybinding to insert the hostname that you are running Cluster SSH from; that might be handy if you were rsyncing data from your controlling machine to all the nodes in the session.

You can specify the user to log in to the remote hosts with using the -l option. A username specified this way has higher priority than any usernames specified in your clusters file.

A collection of terminal configuration parameters for your csshrc file let Cluster SSH use a different terminal than xterm for the connections. Unfortunately, getting gnome-terminal or konsole to work as the terminal is not as trivial as specifying terminal = konsole because Cluster SSH sends information to the terminal with the assumption that it will accept xterm options. I found that terminal = Eterm works as a drop-in replacement if you are fond of that terminal. However, issues like Cluster SSH always passing -font options when starting the terminal make gnome-terminal unsuitable as a drop-in replacement. To get other terminals to work you might have to create a wrapper script that forwards to the terminal only arguments that will not upset it.

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