switch-root, init, SIGHUP

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Subject: switch-root, init, SIGHUP

From: "James Muir (jamesmui)" <jamesmui@xxxxxxxxx>

Date: Sat, 18 Jan 2025 05:40:17 +0000

Accept-language: en-CA, en-US

I have a program, init-jm, that forks and executes /usr/lib/systemd/systemd in the parent (using execl() ) while the child collects some stats in a loop.

The child sets its argv[0][0] to ‘@’.

init-jm is invoked using the “init” kernel parameter on a switch-root system (it’s Fedora 41).

Can someone explain why systemd (PID 1) sends SIGHUP to the child?

This happens just before the statement log_execution_mode(&first_boot) is executed inside main().

Sending SIGHUP to the child seems to be particular to the re-execution of the systemd binary during switch-root because it is not sent when init-jm is invoked using “rdinit”.

Thanks,

-James M