Blog/Home is where your screen session is

In this article I want to take a small note on how I configured a systemd unit to automatically start a detatched screen session.

I want to always have a screen session started for my users (mainly root and my unprivileged users).

Enable the systemd user instance.

Run (as root): loginctl enable-linger myuser.

This will enable the startup of an unprivileged systemd session. It will automatically start user units.

Create the user unit

Make sure the unit directory exists: mkdir -p ~/.config/systemd/user

Create the file name ~/.config/systemd/user/screen-default.service with the following contents:

[Unit]
Description=Default Screen session

Wants=default.target
After=default.target

[Service]
Type=simple
ExecStart=screen -DmS default
Restart=always
RestartSec=3
StartLimitBurst=1

[Install]
WantedBy=default.target

Enable and start

As simple as running systemctl --user enable --now screen-default.service

Screen parameters details

This is interesting:

• -D start screen in detached mode, but does not perform e fork before starting
  • This means that the main process will not exit (and systemd will be able to track it)
  • screen wil exit when the session terminates
  • -d would perform a fork
• -m ignores the $TTY environment variable, so it will not complain
• -s default sets the session name to default

Other interesting parameters

The Restart/RestartSec/StartLimitBurts make it possible for systemd to always restart the unit.

Meaning that there will always be a screen session ready.

A copy-paste ready version

So I've done it a few times and I guess it's better to have a single copy-paste ready version

# sudo loginctl enable-linger `whoami`
mkdir -p ~/.config/systemd/user

cat > ~/.config/systemd/user/screen-default.service <<EOF
[Unit]
Description=Default Screen session

Wants=default.target
After=default.target

[Service]
Type=simple
ExecStart=screen -DmS default
Restart=always
RestartSec=3
StartLimitBurst=1

[Install]
WantedBy=default.target
EOF

systemctl --user enable --now screen-default.service

My .screenrc

To make this post complete, here is my .screenrc:

defmousetrack off
mousetrack off

## details about RUNNING_IN_SCREEN later
setenv RUNNING_IN_SCREEN t 

# might be needed on mac os
#shell "/opt/homebrew/bin/bash"

## get out of my way...
startup_message off

defflow off

layout new default
layout select default
layout autosave on

hardstatus on
hardstatus alwayslastline
# hardstatus string "$USER@%H > %S > %-w | %t | %+w "
hardstatus string "%{.kr}%3`>%{..g}%2`>%{.kw}%-w >%{.kG}%t%{.kw}< %+w %=%{..g}|%l|%{..y} %1`"
backtick 0 3600 3600 whoami
backtick 1 10 10 date "+%d/%m/%y %H:%M"
backtick 2 10 3600 sh -c 'screen -ls | grep --color=no -o "$PPID[^[:space:]]*" | cut -d. -f 2'
backtick 3 3600 3600 hostname

## remove lock screen feature
bind x