This allows for instance to reject switching into a configuration, while
still allowing to reboot into that same configuration.
This can be useful for instance to reject switching to a configuration
with a new systemd major version, but setting that same configuration as
the new boot default with `switch-to-configuration boot` is fine.
A couple of improvements:
1. Avoid the generally discouraged apply argument to options, as it has
quite weird semantics
2. Avoid issues when a user calls a preSwitchCheck `script`, which
would've been silently overridden by the existing implementation.
Reliance on a special attribute name like that is bound to lead to a
very-hard-to-debug problem for someone at some point
3. Use writeShellApplication so that the preSwitchChecks are checked by
shellcheck and and so that they run with basic bash guardrails
4. Fix shellcheck issue (testing the value of $?)
5. Add a positive preSwitchCheck to the nixos test, to make sure that
that works as intended
We need to take the "top" mount instead of any mount, which is the last
line printed by findmnt. Additionally, make the regex more strict, so we
don't select mount options ending in ro (like `errors=remount-ro` from
ext4, or overlay paths ending in 'ro') and accidentally leave the Nix
store RW after boot.
Prior to this change a service failure would occur when this tmpfiles
service did not finish fast enough and receive a SIGTERM from systemd.
Additionally, `initrd-nixos-activation` is already ordered with
`After=initrd-switch-root.target`.
These daemons should not be stopped, as they're foundational to a
proper functioning of the system. When switching configurations, they
only need a restart instead of that stop/start cycle.
Helps the following situation:
- SSH in initrd is enabled
- NixOS is waiting for a password to be typed at the console (or
provided via cryptsetup-askpass)
- The user logs in via SSH, but instead of running cryptsetup-askpass,
they run "cryptsetup open" directly (because they don't know that
they need to use NixOS's cryptsetup-askpass script, or because they
want to use a non-trivial unlocking method that is not natively
supported by this module)
Currently, in the above situation, NixOS will keep waiting for a
password to be entered even though the device is already unlocked. If
a password is entered, it will print a confusing "already exists"
error and keep asking for the same password.
We can improve on this by simply checking if the device is already
unlocked in our read loop. In this case, we don't need to do anything
other than return from the function and continue booting.
Removing the splash param only causes plymouth to display console
output by default; it still runs. Systemd stage 1 respects this flag
due to unit conditions preventing plymouth from even running. So this
brings parity to scripted stage 1.
