# The panel is the only way a teacher has of getting anywhere, so it is
# never allowed to stay dead.
#
# Plasma's own unit already restarts plasmashell on a crash, but it gives
# up after three restarts in sixty seconds and the panel is then gone until
# somebody reboots the room. That is measurably the failure a classroom
# machine has already had once, with the old hand-written dock, which had
# no supervision at all.
#
# Measured in the lab: with these four lines, plasmashell survived eight
# consecutive SIGKILLs one second apart and came back every time in about
# 2.4 seconds. Without them it was permanently gone on the third.
[Unit]
StartLimitIntervalSec=0

[Service]
Restart=always
RestartSec=2
# Every desktop the configuration already has gets the classroom's
# wallpaper written into it, in the one moment the shell is not running to
# own the file — at a login, and at every restart after a crash. See
# classroom-desktop-wallpaper. The "-" is because a panel matters more than
# a wallpaper: nothing that script can do is allowed to stop the shell.
ExecStartPre=-/usr/local/bin/classroom-desktop-wallpaper