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  3. 18 May, 2017 1 commit
    • intrigeri's avatar
      Return to the initramfs (unpacked in /run/initramfs) on shutdown (refs:... · 888ccc5a
      intrigeri authored
      Return to the initramfs (unpacked in /run/initramfs) on shutdown (refs: #12428, #12354, Debian#778849).
      
      … otherwise the aufs read-write (tmpfs) branch, among possibly other things,
      can't be properly unmounted and its content remains in memory.
      
      Notes:
      
       * We have to handle some unmounting ourselves in initramfs-pre-shutdown-hook:
         systemd-shutdown doesn't manage to unmount the aufs read-write
         branch (/oldroot/lib/live/mount/overlay) as it is needed by the
         aufs (/oldroot) filesystem, and reciprocally it cannot unmount /oldroot as it
         is kept busy by /oldroot/lib/live/mount/*. So we disentangle this mess
         ourselves. And we have to manually empty the aufs read-write (tmpfs) branch,
         otherwise for some reason its content remains in memory. This code will of
         course need to be adapted for overlayfs some day.
      
       * We lock /bin/kill in memory: apparently systemd-exit.service needs it.
      
       * We remount /run on shutdown *before* dropping caches, just in case dropping
         caches removes what we've locked into memory.
      
       * We unpack the initramfs to /run/initramfs at *boot* time: sadly, I was not
         able to have it unpacked reliably in udev-watchdog-wrapper when the boot
         medium is ejected, so we'll use a little bit more RAM (instead of locking the
         compressed initramfs into memory, we're storing the uncompressed one there)
         and probably slow down the boot a bit, in order to make emergency shutdown
         robust. Note, however, that we save some of the RAM used by the uncompressed
         initramfs by deleting the worst offenders (kernel modules).
      
       * For now the whole procedure is quite noisy on the screen: the pre-shutdown
         hook runs under "set -x", doesn't run "clear", and spits out lots of
         debugging information. The goal is to enable users to provide useful
         debugging data if they have problems with emergency shutdown. Once we have
         shipped this code in a few releases and trust it's robust enough, we can
         surely reconsider and polish the UX by making the output less noisy.
      
       * We use absolute paths in many places to avoid $PATH lookup which might
         fail if the root filesystem is not there anymore.
      888ccc5a