Re: Help required for configuring a blocking service during shutdown

[Michael Biebl <mbiebl@xxxxxxxxx>]

Would the systemd inhibit interface be an option?

https://www.freedesktop.org/wiki/Software/systemd/inhibit/

It was designed for that use case after all.

Am Mo., 29. Aug. 2022 um 14:01 Uhr schrieb Mantas Mikulėnas <grawity@xxxxxxxxx>:
>
> On Mon, Aug 29, 2022 at 1:31 PM Henning Moll <newsScott@xxxxxx> wrote:
>>
>> Hi,
>>
>> back in the rcX days I configured a backup system which blocks a system shutdown in a certain state (network and mounts still active) if a backup is still running. The init script looks like this:
>>
>> ...
>> case "$1" in
>> ...
>>   stop)
>>     plymouth --ping
>>     if [ $? -ne 0 ]; then
>>       log_daemon_msg "waiting for running backup" "backup"
>>     else
>>       plymouth message --text="waiting for running backup"
>>     fi
>>     sleep 10
>>     logger -t backup "rcS: trying to get lock..."
>>     exec {FD}<>"$LOCKFILE"
>>     {
>>       logger -t backup "locked rsync_wrapper: waiting for lock"
>>       flock ${FD}
>>     }
>>     logger -t backup "rcS: continue shutdown..."
>>     plymouth message --text=""
>>
>> ...
>> esac
>> ...
>>
>> The strategy is to wait for a successful lock on a shared LOCKFILE.
>>
>> Now, I want to solve this with systemd. I've read tons of documentation but I don't get it, all my experiments failed. I am using Linux Mint 21 "Vanessa", which is based on Ubunut 22.04.
>>
>> I am looking for a solution which
>>
>> * "pauses" a shutdown or reboot attempt as long as the LOCK cannot be obtained (which means the backup is still running)
>> * while the network connection (ethernet) is still active
>> * and all mounts (local, usb and cifs) are still active
>> * openssh-server still running
>> * The logging functionality (plymouth / log_daemon) would be nice. so the system should be allowed to shutdown to a stage where plymouth is already visible
>>
>> Can you please help me?
>>
>> Best regards
>> Henning
>
>
> Probably similar to what you already have – create a service that starts on boot (doing nothing) and delays the *stop* action. (You'll probably need to start with [Service] Type=oneshot, RemainAfterExit=yes, TimeoutStopSec=1d.) If you list After=ssh.service as a dependency, then your service will be started after OpenSSH and *stopped before OpenSSH*, same with NetworkManager. (I'm not sure if there's a dependency that can be used to target manually done SMB mounts, although remote-fs.target might work for the ones in fstab?)
>
> Not sure how it works with Plymouth, but in its default console output, systemd itself will already show which services are waiting to be stopped. Syslog (journald) should be available the entire time.
>
> The backup system should also run under `systemd-inhibit --what=shutdown` as an additional layer of precaution – that way the user will know that something is still running *before* they initiate the actual shutdown.
>
> --
> Mantas Mikulėnas