Public bug reported:
in Ubuntu Core we default to using panic=-1 on the kernel command line
(documented at [1]) to speed up the auto-rollback mechanism of the
kernel. on a kernel level this works just fine and the system reboots
immediately ...
when in the initramfs during boot and a panic occurs, no reboot happens
at all, the initrd spawns a shell regardless of the panic= value ...
this is caused by a filter in /usr/share/initramfs-tools/init
panic=*)
panic="${x#panic=}"
case ${panic} in
*[![:digit:].]*)
panic=
;;
esac
;;
this function only lets positive values through, else panic= simply gets
unset
the panic() function itself is also not capable of handling negative
values, it has a sleep call that interprets negative values as
commandline options instead of simply ignoring a negative sleep time [2]
(line 11).
the filter in the init script should allow the -1 value (to comply with
the kernel documentation and behaviour) and the panic() function should
properly skip the sleep call when a negative value for panic= is set.
[1]
https://github.com/torvalds/linux/blob/v4.17/Documentation/admin-guide/kernel-parameters.txt#L2931
[2] https://paste.ubuntu.com/p/mswD8Cd869/
** Affects: initramfs-tools (Ubuntu)
Importance: Undecided
Status: New
** Affects: initramfs-tools (Ubuntu Xenial)
Importance: Undecided
Status: New
** Affects: initramfs-tools (Ubuntu Bionic)
Importance: Undecided
Status: New
** Tags: rls-ee-incoming
** Also affects: initramfs-tools (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: initramfs-tools (Ubuntu Bionic)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1831252
Title:
panic=-1 is completely ignored by the initrd causing unexpected
behaviour
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