Determining when a guest booted / how long it's been running

[wferi at niif.hu]

daggs <daggs at gmx.com> writes:

> I'd assume that saying vm running you mean that the os is up and
> running too.  I have similar need, I was able to get something as such
> to work using virsh console when the guest was a linux with serial
> console support enabled.  I wasn't able to get this to work in a
> script as I was never able to terminate the console seesion as virsh
> console wasn't able to send the termination combination properly.

I wouldn't have assumed this meaning, but running off the tangent
anyway: I think installing a guest agent could help solving this
problem.  However, if you want something extremely lightweight, the
following (a custom one-line guest agent if you wish) worked for me:

1. Add a channel with a descriptive name to the guest config:

   <channel type="unix">
     <target type="virtio" name="startup_signal"/>
   </channel>

2. After starting the domain, query the assigned socket path:

   virsh dumpxml $domain | xmllint --nonet --xpath \
   "string(/domain/devices/channel[@type='unix' and target/@name='startup_signal']/source/@path)" -)

3. Then wait for the signal (and optionally acknowledge it):

   socat UNIX-CONNECT:"$socket_path" \
      SYSTEM:'read msg id && [ $msg = ready ] && echo ack $id'

This will wait until you send the signal from the chosen point of the
guest bootup procedure via something like:

port=/dev/virtio-ports/startup_signal
msg=foobar
reply="$(echo "ready $msg" | socat STDIO "$port")"
[ "($reply)" = "(ack $msg)" ] # for checking proper acknowledgment

I folded this into a oneshot systemd service on Linux, but the
implementation should be similarly simple under any OS.
-- 
Feri