How to ensure that there is a delay before a service is started in systemd

Question

I am having a service that depends on Cassandra coming up gracefully and the cluster being up and ready   To ensure that the dependency order is met  I have the following unit file    Unit  Requires cassandra service After cassandra service   Service  Environment JAVA HOME  usr java jre ExecStart  bringup instance path  webapps bringup-app bin bringup TimeoutStartSec 0 ExecStop  PIDFile  bringup instance path  logs bringup pid Restart always   Install  WantedBy multi-user target   How do I ensure that the bringup-app process waits for 30 seconds before it attempts to start up   Currently although it is started after Cassandra  I have noticed that the Cassandra cluster is not up yet and hence any attempt from the bringup-app to connect to Cassandra as part of startup fails    I therefore want to add a delay  Is that possible via the unit file

User · Answer

You can create a  timer systemd unit file to control the execution of your  service unit file   So for example  to wait for 1 minute after boot-up before starting your foo service  create a foo timer file in the same directory with the contents    Timer  OnBootSec 1min   It is important that the service is disabled  so it doesn t start at boot   and the timer enabled  for all this to work  thanks to user tride for this    systemctl disable foo service systemctl enable foo timer   You can find quite a few more options and all information needed here  https   wiki archlinux org index php Systemd Timers

User · Answer

You can run the sleep command before your ExecStart with ExecStartPre     Service  ExecStartPre  bin sleep 30

User · Answer

The systemd way to do this is to have the process  talk back  when it s setup somehow  like by opening a socket or sending a notification  or a parent script exiting    Which is of course not always straight-forward especially with third party stuff     You might be able to do something inline like  ExecStart  bin bash -c   bin start cassandra  amp   do bash loop waiting for it to come up here    or a script that does the same   Or put do bash loop waiting for it to come up here in an ExecStartPost  Or create a helper  service that waits for it to come up  so the helper service depends on cassandra  and waits for it to come up  then your other process can depend on the helper service    May want to increase TimeoutStartSec from the default 90s as well

User · Answer

Combining the answers from  Ortomala Lokni and  rogerdpack  another alternative is to have the dependent service monitor when the first one has started   done the thing you re waiting for  For example  here s how I am making the fail2ban service wait for Docker to open port 443  so that fail2ban s iptables entries take priority over Docker s    Service  ExecStartPre  bin bash -c   while   nc -z -v -w1 localhost 443  gt   dev null  do echo  quot Waiting for port 443 to open    quot   sleep 2  done   sleep 2   Simply replace nc -z -v -w1 localhost 443 with a command that fails  non-zero exit code  while the first service is starting and succeeds once it is up  For the Cassandra case  the ideal would be a command that only returns 0 when the cluster is available

User · Answer

This answer on super user I think is a better answer  From https   superuser com a 573761 67952   But since you asked for a way without using Before and After  you can use   Type idle   which as man systemd service explains     Behavior of idle is very similar to simple  however  actual execution of the service program is delayed until all active jobs are dispatched  This may be used to avoid interleaving of output of              shell services with the status output on the console  Note that this type is useful only to improve console output  it is not useful as a general unit ordering tool  and the effect of this              service type is subject to a 5s time-out  after which the service program is invoked anyway

User · Answer

Instead of editing the bringup service  add a post-start delay to the service which it depends on  Edit cassandra service like so   ExecStartPost  bin sleep 30   This way the added sleep shouldn t slow down restarts of starting services that depend on it  though does slow down its own start  maybe that s desirable

[systemd] How to ensure that there is a delay before a service is started in systemd?

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