Re: [systemd-devel] mount-on-demand for backups; hooks for indicating success/failure

[Jonathan Dowland]

On Fri, Mar 31, 2017 at 12:01:11PM +0200, Lennart Poettering wrote:
> On recent systemd versions you can plug in a script in ExecStop= of
> your backup service, and check the $SERVICE_RESULT env var which tells
> you the success state of the service, which you can then use to set
> any LEDs you like.

This looks very useful, thanks - but the issue here is that I don't
think systemd provides a guarantee that if my backup service Requires
a mount unit, and that mount unit is marked StopWhenUnneeded=true, that
the this script will fire after the unmount has finished (and
succeeded).

I think Michal's solution of having a separate service for the LEDs
might work, perhaps with After=media-ipod.mount, but I need to
experiment some more.

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Jonathan Dowland
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Re: [systemd-devel] mount-on-demand for backups; hooks for indicating success/failure

[Lennart Poettering]

On Thu, 09.03.17 15:53, Jonathan Dowland (jon+systemd-de...@alcopop.org) wrote:

> Hey,
> 
> I have some backup services which depend on mounts. I want those
> filesystems unmounted when the backup jobs are not running. This is
> easily achieved with StopWhenUnneeded.
> 
> I also want to trigger the backup jobs to start when I attach my
> external HDD. This is reasonably simple by adding WantedBy=
> to the backup service (*not* the mount unit, or it will never be
> auto-unmounted).
> 
> So far so good!
> 
> However, this is a headless box and I want to blink an LED when certain
> jobs are running, finish or fail. So I need to execute commands in
> certain situations. Job failure is easy, I can use OnFailure= and set up
> a oneshot service. Job started isn't too bad, I add a ExecStart=-
> to my backup service before the real one.
> 
> Signalling "device is safe to remove" I have not figured out.
> Using a chain of blah.device -> blah.mount -> backup-blah.service units,
> "safe to remove" LED should only happen after the mount has completed
> unmounting, successfully. Is there an existing "hook" or place that I
> could put that in this situation?

On recent systemd versions you can plug in a script in ExecStop= of
your backup service, and check the $SERVICE_RESULT env var which tells
you the success state of the service, which you can then use to set
any LEDs you like.

Lennart

-- 
Lennart Poettering, Red Hat
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Re: [systemd-devel] mount-on-demand for backups; hooks for indicating success/failure

[Michal Sekletar]

On Thu, Mar 9, 2017 at 4:53 PM, Jonathan Dowland
 wrote:
> Hey,
>
> I have some backup services which depend on mounts. I want those
> filesystems unmounted when the backup jobs are not running. This is
> easily achieved with StopWhenUnneeded.
>
> I also want to trigger the backup jobs to start when I attach my
> external HDD. This is reasonably simple by adding WantedBy=
> to the backup service (*not* the mount unit, or it will never be
> auto-unmounted).

WantedBy=device sounds like a weird hack to me. I think that it would
be better to use SYSTEM_WANTS in udev rules instead.

>
> So far so good!
>
> However, this is a headless box and I want to blink an LED when certain
> jobs are running, finish or fail. So I need to execute commands in
> certain situations. Job failure is easy, I can use OnFailure= and set up
> a oneshot service. Job started isn't too bad, I add a ExecStart=-
> to my backup service before the real one.

OnFailure is fine and ExecStart before starting backup also sounds reasonable.

>
> Signalling "device is safe to remove" I have not figured out.
> Using a chain of blah.device -> blah.mount -> backup-blah.service units,
> "safe to remove" LED should only happen after the mount has completed
> unmounting, successfully. Is there an existing "hook" or place that I
> could put that in this situation?

It should be possible to achieve this with normal dependencies. For
example, you would have blink-successful.service that would Require
backup service and would be ordered after it.

Dependencies should then look like this,
# backup.service
[Unit]
Wants=blink-successful.service

# blink-successful.service,
[Unit]
Requires=backup.service
After=backup.service

backup.service pulls in blink service and that will run only when
backup succeeded.

>
> My temporary solution is to remove the mount unit entirely, define the
> mount point in /etc/fstab and use ExecStart and ExecStop in the backup
> service to mount and umount before and after the job runs:
>
> [Unit]
> OnFailure=blinkstick-fail.service
> [Service]
> ExecStart=/bin/mount /media/ipod

I'd leave fstab entry in place and replace ExecStart=/bin/mount with
RequiresMountsFor=/media/ipod (this belongs to [Unit] section). So
when this service is started it will pull in mount unit to transaction
and gets ordered after the mount unit.

Michal
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[systemd-devel] mount-on-demand for backups; hooks for indicating success/failure

[Jonathan Dowland]

Hey,

I have some backup services which depend on mounts. I want those
filesystems unmounted when the backup jobs are not running. This is
easily achieved with StopWhenUnneeded.

I also want to trigger the backup jobs to start when I attach my
external HDD. This is reasonably simple by adding WantedBy=
to the backup service (*not* the mount unit, or it will never be
auto-unmounted).

So far so good!

However, this is a headless box and I want to blink an LED when certain
jobs are running, finish or fail. So I need to execute commands in
certain situations. Job failure is easy, I can use OnFailure= and set up
a oneshot service. Job started isn't too bad, I add a ExecStart=-
to my backup service before the real one.

Signalling "device is safe to remove" I have not figured out.
Using a chain of blah.device -> blah.mount -> backup-blah.service units,
"safe to remove" LED should only happen after the mount has completed
unmounting, successfully. Is there an existing "hook" or place that I
could put that in this situation?

My temporary solution is to remove the mount unit entirely, define the
mount point in /etc/fstab and use ExecStart and ExecStop in the backup
service to mount and umount before and after the job runs:

[Unit]
OnFailure=blinkstick-fail.service
[Service]
ExecStart=/bin/mount /media/ipod
# vvv this is a "backup in progress" colour vvv
ExecStart=/usr/local/bin/blinkstick --index 1 --limit 10 --set-color 33c280
ExecStart=/usr/bin/rsync ... # the backup job
ExecStop=/bin/umount /media/ipod
ExecStop=/usr/local/bin/blinkstick --index 1 --limit 10 --set-color green

This works for this simple use-case, but is not very elegant, and I
don't think I can scale this up to my next task: do the same but for an
*encrypted* filesystem. So here I have to have  ->
systemd-crpytsetup@.service -> .mount (or not?) ->
backup-black.service.


Any advice appreciated. Thanks!


-- 
Jonathan Dowland
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