Systemd – How to List All Services That Start After a Certain Service

systemd

I would like to find in this way (if possible) which services wait for NetworkManager-wait-online.service to execute before they start?

Best Answer

I think the command you are looking for is:

$ systemctl list-dependencies --reverse NetworkManager-wait-online.service 
NetworkManager-wait-online.service
● └─network-online.target
●   └─hddtemp.service

From man systemctl:

   list-dependencies [NAME]
       Shows units required and wanted by the specified unit. This
       recursively lists units following the Requires=, Requisite=,
       ConsistsOf=, Wants=, BindsTo= dependencies. If no unit is
       specified, default.target is implied.

       By default, only target units are recursively expanded. When --all
       is passed, all other units are recursively expanded as well.

       Options --reverse, --after, --before may be used to change what
       types of dependencies are shown.

   --reverse
       Show reverse dependencies between units with list-dependencies,
       i.e. follow dependencies of type WantedBy=, RequiredBy=, PartOf=,
       BoundBy=, instead of Wants= and similar.

Related Solutions

Ubuntu – Systemd: How to start/stop services on battery

I'm not an expert on systemd, but I google better than the average bear. See https://wiki.archlinux.org/index.php/Power_management:

There is just one thing systemd cannot do (as of systemd-204): power management depending on whether the system is running on AC or battery. To fill this gap, you can create a single udev rule that runs a script when the AC adapter is plugged and unplugged:

Further instructions follow.

My guess is you want to do something like create a fake service called acpluggedin.service which is started and stopped by the udev rule, and then have the mongo and redis services Requires it. Or something.

systemd – How to Start Service B After Service A Completes

I've come upon an answer to my own question.

I read in the systemd.service man page about the "Type=" clause, and I see that when I add "Type=oneshot" to the [Service] section of my *.service files, systemd does what I wanted.

I expect I could use other Type= settings and get results to my liking, and I also expect that I probably don't actually need to make second.service oneshot to get what I want; first.service is the one I need to see finish. But I have a path to success now.

So, for the record, here are the working *.service files and the journalctl output to prove it.

Onward!

====

First.service:

[Unit]
Description=First of two services

[Service]
ExecStart=/home/steve/play/systemd/oneAfterTheOther/first.sh
Type=oneshot

[Install]
WantedBy=multi-user.target

Second.service:

[Unit]
Description=Second of two services
After=first.service

[Service]
ExecStart=/home/steve/play/systemd/oneAfterTheOther/second.sh
Type=oneshot

[Install]
WantedBy=multi-user.target

Journalctl output:

$ journalctl -u first -u second
-- Logs begin at Wed 2018-09-05 11:46:04 CDT, end at Wed 2018-09-05 11:51:54 CDT
Sep 05 11:46:21 sk-xenial-vm systemd[1]: Starting First of two services...
Sep 05 11:46:22 sk-xenial-vm first.sh[868]: sleep for 10 seconds
Sep 05 11:46:32 sk-xenial-vm first.sh[868]: ...and we're out
Sep 05 11:46:32 sk-xenial-vm systemd[1]: Started First of two services.
Sep 05 11:46:32 sk-xenial-vm systemd[1]: Starting Second of two services...
Sep 05 11:46:32 sk-xenial-vm second.sh[1104]: sleep for 2 seconds
Sep 05 11:46:34 sk-xenial-vm second.sh[1104]: ...and we're out
Sep 05 11:46:34 sk-xenial-vm systemd[1]: Started Second of two services.

Best Answer

Related Solutions

Ubuntu – Systemd: How to start/stop services on battery

systemd – How to Start Service B After Service A Completes

Related Question