[systemd-bugs] [Bug 79497] New: OnUnitActiveSec triggers when timer unit starts

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79497

          Priority: medium
            Bug ID: 79497
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: OnUnitActiveSec triggers when timer unit starts
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: jimc at jfcarter.net
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

This is with systemd-208 from OpenSuSE-13.1 package systemd-208-19.1.x86_64
Systemd units are all in /etc/systemd/system .
They are appended at the end of this report.  

baobei.automount starts at boot. If you do "ls /baobei", baobei.mount runs.
baobei.mount does mount the filesystem.  Also starts baobei-umount.timer
The timer triggers immediately but fails to unmount because /baobei is busy.
5 minutes later (more or less), baobei-umount.service ran and unmounted it.
And baobei-umount.timer was stopped.  

10 mins later, "ls /baobei", it gets mounted, baobei-umount.timer started.
The timer triggers immediately but fails to unmount because it's busy.
30 secs later, "umount /baobei", it was unmounted, baobei-umount.timer stopped.
90 secs later, "ls /baobei", it gets mounted,
    baobei-umount.timer was started, baobei-umount.service was NOT executed.
180 secs later,  baobei-umount.service was started and
    successfully unmounted /baobei.  baobei-umount.timer was stopped.

The 180 secs is 300 secs after baobei-umount.service was previously 
started (and didn't unmount /baobei because it was busy).  

The man page for systemd.timer says:
If a timer configured with OnBootSec= or OnStartupSec= is already
in the past when the timer unit is activated, it will immediately
elapse and the configured unit is started. This is not the case for
timers defined in the other directives.

Evidently the last statement is not presently operative. 

What I would like the developers to do: Once again prevent the timer 
from triggering if one of its contingencies is true at startup.  

The following is actually a feature request, to get the developers
thinking about how some people want to use timers.  
A common use-case for the timer is to stop a unit, rather than to 
start it.  If the timer had a StopUnit option, baobei-umount.service
would not be needed.  But if you stop baobei.mount and the mount point
is busy, I assume something reasonable happens.  

I tried hard to set up socket activation for cups (printing), but failed. 
I wanted cups to be stopped a certain time after being started, but the 
timer triggered immediately and the killer service killed cups which had
just been started.  It seems bizarre for the killer service to exec
"systemd stop cups.service".  I tried a Conflicts contingency, but was
not able to get it to work right.  If the timer could do the StopUnit
thing, life would be a lot simpler.  

The real autofs daemon unmounts unused filesystems after a configured
time.  If systemd's automount unit had an auto-unmount timer, a lot of
this complication could be avoided.  In fact, the same is true for 
socket units, for which you can assume that the underlying service is
unused if no packets go through its socket.  A race condition needs to 
be worked around, if systemd declares a unit unused and stops it, but
after committing to stop, the automount reports access or the socket
receives a packet.  

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 520 Portola Plaza; Los Angeles, CA, USA  90095-1555
Email: jimc at math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)


Systemd units:
=-=-= baobei.automount -- Starts baobei.mount when the mount point 
    is referred to.

[Unit]
Description=Automount Baobei's virtual disc

[Automount]
Where=/baobei

[Install]
WantedBy=local-fs.target

=-=-= baobei.mount -- Actually mounts the filesystem.

[Unit]
Description=Mount Baobei's virtual disc

[Mount]
What=/dev/sda7
Where=/baobei
Type=ntfs
Options=ro,loop,offset=103424K,umask=222,uid=alice

=-=-= baobei-umount.timer -- Try to unmount the filesystem after 5 minutes.

[Unit]
Description=Delays before auto-unmounting Baobei's virtual disc

# When baobei.mount is started or stopped by systemd operations, this unit 
# is started/stopped too.  
PartOf=baobei.mount

# If baobei.mount stops for any reason, this one stops too, e.g. if you
# manually umount /baobei.  If this unit is started explicitly, baobei.mount
# will be too (same as Requires).
BindsTo=baobei.mount

After=baobei.mount

[Timer]
OnActiveSec=300
OnUnitActiveSec=300

# Unit=baobei-umount.service (is the default and is recommended)

[Install]
WantedBy=baobei.mount

=-=-= baobei-umount.service -- Actually unmounts the disc.

[Unit]
Description=Unmounts Baobei's virtual disc

[Service]
Type=oneshot

ExecStart=/usr/bin/umount /baobei

# This is the return code of umount if the mtpt is not mounted or is busy.
SuccessExitStatus=32

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