automatic reboot fails with non executable empty systemd

[Federico Gimenez]

Steps to reproduce:

Begin with an upgradable image

$ sudo ubuntu-device-flash --revision=-1 core rollling --channel edge -o snappy.img --developer-mode

Launch

$ kvm -m 768 -redir :8022::22 ./snappy.img

Update

$ ssh -p 8022 ubuntu@localhost
$ sudo snappy update

Remove /lib/systemd/systemd file in the other partition and create a zero size file:

$ sudo mount -o remount,rw /writable/cache/system
$ sudo rm /writable/cache/system/lib/systemd/systemd
$ sudo touch /writable/cache/system/lib/systemd/systemd

Reboot. The system hangs and is unable to reboot by itself to the previous partition.

The reported error on boot is:

  target filesystem doesn’t have requested /lib/systemd/systemd
  /bin/sh: 0: can’t access tty; job control turned off

If the empty /lib/systemd/systemd has the execute permission all goes fine and the system reboots to the working partition after the failed boot.

[Michael Vogt (mvo)]

Failed to reproduce on armhf/15.04, I tried to create a empty systemd that is not 755 and kernel paniced and rebooted.

However I can confirm that it hangs on amd64/rolling:
"""
[ 181.700024] reboot: Restarting system
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Initializing cgroup subsys cpuacct
[ 0.000000] Linux version 4.0.0-4-generic (buildd@brownie) (gcc version 4.9.3 (Ubuntu 4.9.3-1ubuntu1) ) #7-Ubuntu SMP Thu Jul 9 15:17:01 UTC 2015 (Ubuntu 4.0.0-4.7-generic 4.0.7)
[ 0.000000] Command line: BOOT_IMAGE=(hd0,gpt2)/EFI/ubuntu/grub/b/vmlinuz root=LABEL=system-b ro init=/lib/systemd/systemd console=ttyS0 console=tty1 panic=-1
...
[ 3.356557] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8042/serio1/input/input3
"""
nothing else.

[Zygmunt Krynicki (zyga)]

I'm marking this bug as won't fix as it was reported in snapd 15.04 era. Please re-open with updated information if the original issue is still a problem for you.