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I have a virtualization server to which I connect over ssh. If I now change the size of the window it will automatically propagate to the server. It's most easily seen using stty -a, checking the columns and row values.

I then use virsh console to connect to the serial interface on a KVM based virtual machine. When I now change the size of the window it does not propagate to the virtual server. This is most easily seen by checking stty -a, which is not updated on the virtual machine when I change window size. This means that line breaks does not work correctly in the terminal and any application that relies on window size for formatting (emacs, man, etc) gets messed up unless the window size on the client matches the default size on the server.

A workaround is to manually set the window size to match the client window using stty, but I wonder if there is any way to get this information to propagate and set the window size in the virtual machine automatically.

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2 Answers

up vote 1 down vote accepted
+150

You could mostly work around this problem in the shell.

The command:

eval `/usr/bin/resize`

will set the COLUMNS and LINES shell variables appropriately and then export them. So in bash, you could add the following to your .bash_profile (or .profile, depending on which you use)

PROMPT_COMMAND="eval `/usr/bin/resize`"

Or in zsh:

function precmd {
    eval `/usr/bin/resize`
}

So that a resize would be performed right before each prompt was displayed. The effect wouldn't be like that of ssh or telnet where the window changes would be handled immediately as a result, however I think this is probably the best you'll get.

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A little hacky, but still a good solution. Thank you! –  pehrs Dec 29 '10 at 11:09
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Telnet and SSH has an out of band channel to configure these settings. Serial interface does not. See: http://tools.ietf.org/html/rfc1073 and http://tools.ietf.org/html/rfc4254#page-14

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I kind of figured out that there was a control channel involved. But the question remains, is there a better workaround for consoles of KVM based virtual machines? (I don't mind reconfiguring the machines) –  pehrs Dec 22 '10 at 15:16
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