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How do I restart a Systemd service when a file change. I've got a Java service that I want to reload when any jar file changes.

This is my setup:

srv.service

[Unit]
Description=srv 0.1: Service's description
After=network.target

[Service]
Type=simple
WorkingDirectory=/opt/srv
ExecStart=/opt/srv/bin/srv
User=root
Group=root

[Install]
WantedBy=multi-user.target

srv.path

[Path]
PathModified=/opt/srv/lib/

I also tried using PathChanged and using a file instead a directory.

When I installed the service I executed: sudo systemctl daemon-reload and sudo systemctl enable srv

Thanks!

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7
  • 3
    Not tested so not an answer, but from the documentation it seems that path units are only useful for activating (starting) other units. Here you could probably create srv-restart.path with PathChanged=/opt/srv/lib/ and srv-restart.service with ExecStart=systemctl restart srv.service.
    – Michał Politowski
    Jan 26, 2017 at 12:46
  • It seems that if you name it the same as the service (with .path) the path file refers to the same service: freedesktop.org/software/systemd/man/systemd.path.html however... I don't know if it only starts a service or it even restart it if it is already running
    – jaguililla
    Jan 26, 2017 at 13:12
  • As I understand it from the docs, srv.path can only do the equivalent of systemclt start srv.service, so for automating restarts you will need another service, which when started restarts your service.
    – Michał Politowski
    Jan 26, 2017 at 13:16
  • You need to start it systemctl start srv.path - and to have it started on boot systemctl preset srv.path
    – Michael D.
    Jan 26, 2017 at 13:25
  • 1
    Relevant: github.com/systemd/systemd/issues/4324
    – Michał Politowski
    Jan 26, 2017 at 15:03

2 Answers 2

Reset to default
57

Michal Politowski's comment is exactly correct. I use this method to automatically restart services when new artifacts are deployed. It is very helpful.

To be clear, you need:

srv.service

[Unit]
Description=srv 0.1: Service's description
After=network.target

[Service]
Type=simple
WorkingDirectory=/opt/srv
ExecStart=/opt/srv/bin/srv
User=root
Group=root

[Install]
WantedBy=multi-user.target

srv-watcher.service

[Unit]
Description=srv restarter
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/bin/systemctl restart srv.service

[Install]
WantedBy=multi-user.target

srv-watcher.path

[Path]
PathModified=/opt/srv/lib

[Install]
WantedBy=multi-user.target
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6
  • 16
    Are there any guarantees about when this is triggered if lots of files are getting changed in rapid succession?
    – Rich Remer
    Feb 22, 2018 at 23:29
  • 9
    Is important to remember that the «.path» unit also needs to be enabled. In this case: systemctl enable srv-watcher.path && systemctl start srv-watcher.path
    – Pau Ruŀlan Ferragut
    Apr 13, 2018 at 9:57
  • 1
    If your restart service is not of the same name as the .path file then just add Unit=nameofmyrestart.service to the [Path] section of your .path file. freedesktop.org/software/systemd/man/systemd.path.html#Unit=
    – DKebler
    Mar 19, 2019 at 2:10
  • Works fine in CentOS for restarting Kestrel (ASP.NET Core)
    – Suleman
    Oct 7, 2019 at 5:39
  • 4
    What if you want to run the service after a succession of file changes? i.e. only run it once the consecutive changes stop so we avoid restarting for each change.
    – djuarez
    Mar 3, 2021 at 13:36
18

The answer above is almost great, but it's missing a few things that took me a while to figure out. Others came across the same issues, see the comments section.

systemctl enable srv-watcher.{path,service}
systemctl start srv-watcher.{path,service}

srv.service

[Unit]
Description=srv 0.1: Service's description
After=network.target

[Service]
Type=simple
WorkingDirectory=/opt/srv
ExecStart=/opt/srv/bin/srv
User=root
Group=root

[Install]
WantedBy=multi-user.target

srv-watcher.service

[Unit]
Description=srv restarter
After=network.target
StartLimitIntervalSec=10
StartLimitBurst=5

[Service]
Type=oneshot
ExecStart=/usr/bin/systemctl restart srv.service

[Install]
WantedBy=multi-user.target

srv-watcher.path

[Path]
Unit=srv-watcher.service
PathChanged=/opt/srv/lib 
# trigger on changes to a file not just create/delete
# don't put comments in the same line as the command

[Install]
WantedBy=multi-user.target

If it is working, you will see these messages in journalctl

$: journalctl -f -o cat -u srv-watcher
Starting srv-watcher...                                                                                          
Started srv-watcher.

Other things to note, patch may fire many times but the srv-watcher.service will respect the default limit of 5 restarts in 10 second intervals. https://www.freedesktop.org/software/systemd/man/systemd.unit.html#StartLimitIntervalSec=interval

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3
  • Thanks for your answer-- it really makes sense of the accepted answer. Question: have you looked at putting in explicit "Requires=" or "After=" for the watcher service files? Does it matter and would it work like one would expect?
    – Zchpyvr
    Mar 26, 2020 at 16:46
  • 3
    What if you want to run the service after a succession of file changes? i.e. only run it once the consecutive changes stop so we avoid restarting for each change.
    – djuarez
    Mar 3, 2021 at 13:37
  • Getting Failed to restart srv.service: Interactive authentication required. This is because I have strict access controls on the system & running systemctl might need sudo. kill would need process id for the srv.service but would need some minor scripting to obtain the pid
    – Rajeev Ranjan
    Jul 5, 2023 at 17:10

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