virsh console and tty size

Question

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.

mark · Accepted Answer · 2010-12-27T14:33:33.910

8

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.

edited Dec 27 '10 at 14:33

answered Dec 27 '10 at 14:11

mark

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A little hacky, but still a good solution. Thank you! – pehrs Dec 29 '10 at 11:09
See also this answer to do it without xterm's `resize` command: http://unix.stackexchange.com/a/283206 – rsaw Dec 30 '16 at 20:31

score 3 · Answer 2 · edited Oct 07 '21 at 06:47

3

Telnet and SSH has an out of band channel to configure these settings. Serial interface does not. See: https://www.rfc-editor.org/rfc/rfc1073 and https://www.rfc-editor.org/rfc/rfc4254#page-14

edited Oct 07 '21 at 06:47

Community

1

answered Dec 22 '10 at 15:00

Mircea Vutcovici

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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

Gakis41 · Answer 3 · 2021-05-25T12:58:29.133

1

if resize command is not available in your system you can try something like:

stty rows 45 
stty columns 140

but you have to put it your .bash_profile to persist the change and then source it to see the change

edited May 25 '21 at 12:58

answered Mar 19 '21 at 13:24

Gakis41

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4

score 0 · Answer 4 · answered Nov 30 '19 at 16:18

Just adding to mark's answer, bacause Serverfault does not allow me to comment.

When the target domain is OpenBSD 6.6, resize is located elsewhere and requires the xbase66 set at least.

Additionally, if you are using the default ksh, it is enough to run:

eval `/usr/X11R6/bin/resize`

It is a shame that this is not in Red Hat's KVM Admin Guide.

virsh console and tty size

4 Answers4