# A root shell on %I, for diagnosing a live medium that will not finish.
#
# Gated on `alloy.debug` the same way alloy-installer.service is gated on
# `alloy.installer`: the live system and the installed system are the same
# image, so a unit that could start on an installed machine would be a root
# shell with no password on every Alloy in the world. Only the verbose GRUB
# entries in build/make-iso.sh set the flag, and an installed system's kernel
# arguments come from the image, not from those entries.
#
# It exists because the live medium is otherwise unreachable. There is no
# account on it (the installer creates one on the target, not here), root is
# locked, so a failure inside the live system can only be read off whatever
# the installer happened to print. Diagnosing the read-only mount that
# blocked the configure step meant a full ISO rebuild per question.
#
# Instantiated for tty9 and ttyS0 by the preset: tty9 for a laptop with a
# keyboard in front of it (Ctrl-Alt-F9), ttyS0 for a VM, where the serial
# console is a text log that can be read and searched instead of
# photographed.
#
# tty9 rather than a low-numbered VT because logind auto-spawns a getty on
# the first six VTs as soon as one is switched to, which takes the terminal
# straight back off this unit and offers a login prompt for an account that
# does not exist on a live medium. Observed on tty2; systemd's own
# debug-shell.service picks tty9 for the same reason.
[Unit]
Description=Alloy debug shell on %I
Documentation=https://git.sr.ht/~maxmj/alloy
ConditionKernelCommandLine=alloy.debug
After=systemd-user-sessions.service
Before=getty.target
# Whichever getty owns this terminal has to lose it, and which one that is
# depends on the terminal: serial consoles get serial-getty@, VTs get getty@.
# Naming both is how one template serves both without knowing which it is.
Conflicts=getty@%i.service serial-getty@%i.service

[Service]
# Type=idle for the same reason the installer uses it: let the boot's own
# output finish before taking the terminal.
Type=idle
ExecStart=/usr/bin/bash --login
TTYPath=/dev/%I
StandardInput=tty
StandardOutput=tty
StandardError=journal
TTYReset=yes
TTYVHangup=yes
# A debug shell that does not come back when you exit it is a debug shell
# you get to use once per boot.
Restart=always
RestartSec=1

[Install]
WantedBy=multi-user.target