# Christoph's last Weblog entries

### Entries from February 2011.

20th February 2011

There are many ways to run some commands simultaneously on multiple hosts like cssh or dsh. They come handy for example when you are installing software updates on a set of hosts.

dsh is a rather simple comandline tool allowing to execute a command over ssh on multiple hosts. However it doesn't allow any interactive input -- so you can't look at the potentially upgrading packages and press y to accept and you can't go through debconf promts or similar.

This is solved by cssh which opens a XTerm for every host and a input area that is broadcastet to all of them. this is working really well -- you can execute your update on all hosts and still do individual adjustments just as needed: switch focus from the broadcasted input to one of the terminal windows and anything you type just goes there.

Now cssh has a big disadvantage: it requires a running X server (and doesn't do too well with a fullscreen windowmanager). Requiring X is quite a blocker if you need to run that ssh multiplexer on a remote host, for example if the firewalling doesn't allow direct connections. Fortunately you can make tmux behave as we want -- in a simple terminal:

First you need a script spawning the ssh sessions in separate tmux panes and direct input to all of them -- here called ssh-everywhere.sh (you could also write a tmux config I guess):

#/bin/sh
# ssh-everywhere.sh
for i in $HOSTS do tmux splitw "ssh$i"
tmux select-layout tiled
done
tmux set-window-option synchronize-panes on


Now start the whole thing:

tmux new 'exec sh ssh-everywhere.sh'


And be done.

#### Update

If you want to type in just one pane (on one host) you can do that as well: C-b : set-window-option synchronize-panes off and moving to the right pane (C-b + Arrow keys)

Tags: debian, foss, howto, linux.

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