** Also affects: initramfs-tools (Ubuntu Eoan)
   Importance: Medium
       Status: New

** Tags removed: rls-ee-incoming

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https://bugs.launchpad.net/bugs/1831252

Title:
  panic=-1 is completely ignored by the initrd causing unexpected
  behaviour

Status in initramfs-tools package in Ubuntu:
  New
Status in initramfs-tools source package in Xenial:
  New
Status in initramfs-tools source package in Bionic:
  New
Status in initramfs-tools source package in Eoan:
  New

Bug description:
  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/

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