[systemd-devel] autostart processes based on tty

[Mantas Mikulėnas]

On Mon, May 16, 2016 at 5:09 AM, Emanuel Berg <embe8573 at student.uu.se>
wrote:

> I would like to start different processes in
> different ttys on boot, automatically and with
> autologin first, and then have them run as normal
> programs, with the I/O intact, including quitting
> and get the shell - i.e., just as you would if you
> did it all manually. (The autologin part of the
> above question I solved.)
>
> Up and until today, I've done this with zsh in
> .zprofile, and I include it here so you'll know
> exactly what I ask for:
>
> # ...
>
> local tty_number=${TTY#/dev/tty}
>
> case $tty_number in
>     (1)       lkeys # [1]
>               make -C ~/.emacs.d/emacs-init
>               emacs ;;
>     (2|3)     tmux-new-session-split ;;
>     (5)       echo "Waiting for Internet connection..."
>               when-internet-set-time > /dev/null # ~/.zsh/web
>               tmux ;;
>     (6)       start-x-if-not-running & ;;
> esac
>
> # ...
>
> I thought it'd be a good idea to do it with systemd!
>

~/.zprofile seems just fine for this task – it *is* the zsh "run things on
login" script after all. (And since these are your personal processes,
especially the X stuff, it's much better to have them running *inside* the
login session along with everything else.)

Trying to cram these into systemd .services would only overcomplicate
things.


>
> As a test, I tried to do it with top(1) in
> /dev/tty4, and I got this far
>
>     [Unit]
>     Description=top on tty4
>
>     [Service]
>     Type=simple
>     ExecStart=/usr/bin/top
>     StandardInput=tty
>     StandardOutput=tty
>     TTYPath=/dev/tty4
>     Restart=always
>
>     [Install]
>     WantedBy=getty.target
>
> This results in a running process, but it doesn't
> seem to be associated with /dev/tty4 and there is no
> I/O there but the familiar shell.
>

I'm not sure of the exact conditions, but sometimes (depending on various
[Service] settings) TTYPath= uses exclusive access mode – only one service
at a time is allowed. If it didn't, then you'd have both top and getty
trying to display things *at once*, and trying to read from the keyboard at
once as well.

To make this work at all, you'd need Conflicts=getty at tty4.service and some
way to start the getty@ again once your custom service has exit. Or,
perhaps, Type=oneshot + Before=getty at tty4 + an infinite timeout. (Also
you'd of course need User=emanuel, some PAMName=, and so on – autostarting
top as root isn't the best idea.)


> PS. I would say this is a ".user" question but
>     I couldn't find such a group!
>

For the time being, systemd-devel@ is multipurpose. It doesn't really
receive enough traffic to warrant separation, IMHO.

-- 
Mantas Mikulėnas <grawity at gmail.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/systemd-devel/attachments/20160516/a52e6820/attachment.html>