Boot fails if /sbin/init (or init= arg) is an absolute symlink

[Martin Pitt]

Booting current Utopic with init=/bin/systemd fails., or installing systemd-sysv fails. In both cases we are dealing with an absolute symlink "/bin/systemd -> /lib/systemd/systemd" or "/sbin/init -> /lib/systemd/systemd". I see:

/init: line 307: readlink: not found
Target filesystem doesn't have requested /bin/systemd
and then a kernel panic.

[Martin Pitt (pitti)]

This is coming from "init" line284:

                 case $(readlink "${rootmnt}${checktarget}") in /*)

That's the readlink that isn't found (not the chrooted one in the next line). I added a few debugging steps, and "type readlink" says "readlink is readlink". I cannot reproduce this in break=bottom, in the interactive shell readlink /root/bin/systemd works just fine. But as soon as I Ctrl+D, readlink doesn't work any more. Some subtle busybox difference between interactive and shell script mode?

It works if I replace this with

                 case $(/bin/busybox readlink "${rootmnt}${checktarget}") in /*)

but that's not a proper solution but a workaround.

[Martin Pitt (pitti)]

Moreover, this obviously works in Debian, but between Ubuntu's and Debian's initramfs initd there is no obvious difference for readlink.

[Dimitri John Ledkov (xnox)]

I would prefer that /sbin/init is shipped as a real file by systemd-sysv, instead of a symlink of any kind. (E.g. a copy of /lib/systemd/systemd).

[Dimitri John Ledkov (xnox)]

Actually, i take that back. To support running upstart user sessions under systemd-sysv, we'd need to split upstart package. In that case upstart will ship /sbin/init which would be a symlink as well. Similar to how systemd-sysv is packaged.

[Dimitri John Ledkov (xnox)]

 for execvp("readlink"...) to work, there must be /bin/readlink present. I still don't understand why we simply not generate symlinks for all busybox applets present in the initramfs. Anyway, readlink added.

[Launchpad Janitor (janitor)]

This bug was fixed in the package initramfs-tools - 0.103ubuntu8

---------------
initramfs-tools (0.103ubuntu8) utopic; urgency=medium

  * Add readlink symlink for busybox in the busybox hook, needed to
    support /sbin/init as a readlink (LP: #1351295).
 -- Dimitri John Ledkov <email address hidden> Fri, 01 Aug 2014 16:46:35 +0100

[A. Eibach (andi3)]

Strange.

I still got the "line 307: readlink: not found" error on bootup although I do have initramfs-tools 0.103ubuntu8.

[Dimitri John Ledkov (xnox)]

On 7 August 2014 03:03, A. Eibach <email address hidden> wrote:
> Strange.
>
> I still got the "line 307: readlink: not found" error on bootup although
> I do have initramfs-tools 0.103ubuntu8.
>

It's not just initramfs-tools package, one also needs to regenerate
initramfs with that tools package for all kernels you wish to boot.

Reboot to latest kernel; $ sudo update-initramfs -u; reboot again
should do the trick.

--
Regards,

Dimitri.

[A. Eibach (andi3)]

Thank you!
Hmm..."Latest kernel"...that's another interesting thing...always got nothing but black screens in 3.16, hence I had to go back to the 3.13 series (patch levels 30 +) and --- no more problems.

[A. Eibach (andi3)]

$ sudo update-initramfs -k 3.13.0-32-generic -u

voila !! thanks again for leading me in the right direction.
I've decided to post this too here; maybe it will help some more users new to Ubuntu.