Public bug reported:
I reproducibly run into an eternal hang when deploying services with
Juju, when it prepares a new xenial testbed. The current xenial cloud
image does not have the latest snapd, so snapd gets dist-upgraded:
Preparing to unpack .../snapd_2.14.2~16.04_amd64.deb ...
Warning: Stopping snapd.service, but it can still be activated by:
snapd.socket
Unpacking snapd (2.14.2~16.04) over (2.13) ...
Setting up snapd (2.14.2~16.04) ...
[...] hangs
The postinst tries to start snapd.boot-ok.service on upgrade:
|-cloud-init(311)-+-apt-get(577)---dpkg(845)---snapd.postinst(846)---perl(919)---systemctl(922)
| `-sh(354)---tee(355)
root 922 0.0 0.0 25316 1412 pts/0 S+ 06:09 0:00
/bin/systemctl start snapd.boot-ok.service
This hangs eternally because:
- cloud-init's dist-upgrade runs *during* the boot process, so that the
system is not fully booted yet when this happens (see bug 1576692); thus
multi-user.target is *not* yet active
- snapd.boot-ok.service is After=multi-user.target
- "systemctl start" is synchronous by default, i. e. it waits until the
service is started unless you use --no-block.
Thus snapd.postinst waits on snapd.boot-ok.service waits on multi-
user.target waits on cloud-init to finish waits on snapd.postinst to
finish.
I think conceptually you shouldn't start snapd.boot-ok.service in the
postinst; if the system is already booted (manual dist-upgrade) it
should already be running, and if it does get upgraded during boot (with
cloud-init) then you shouldn't pretend that booting is already finished.
So I suggest to use dh_installinit with --no-scripts for snapd.boot-
ok.service.
** Affects: snapd (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1621336
Title:
snapd.boot-ok.service hangs eternally on cloud image upgrades
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