An example with an oneshot service on systemd. #systemd #systemd.service #oneshot

README-oneshot-systemd-service.md

README

Services declared as oneshot are expected to take some action and exit immediatelly (thus, they are not really services, no running processes remain). A common pattern for these type of service is to be defined by a setup and a teardown action.

Let's create a example foo service that when started creates a file, and when stopped it deletes it.

Define setup/teardown actions

Create executable file /opt/foo/setup-foo.sh:

#!/bin/bash
echo "Setting up foo ..."
touch /tmp/foo-activated

Create executable file /opt/foo/teardown-foo.sh:

#!/bin/bash
echo "Tearing down foo ..."
if [ -f /tmp/foo-activated ]; then
    rm /tmp/foo-activated
else
    echo "Doesnt seem to be up: Skipping ..."
fi

Define the service unit

Now, we define the systemd unit file as /etc/systemd/system/foo.service. Note that we must specify RemainAfterExit=true so that systemd considers the service as active after the setup action is successfully finished.

[Unit]
Description=Setup foo
#After=network.target

[Service]
Type=oneshot
ExecStart=/opt/foo/setup-foo.sh
RemainAfterExit=true
ExecStop=/opt/foo/teardown-foo.sh
StandardOutput=journal

[Install]
WantedBy=multi-user.target

Reload the systemd daemon and start the service as normally (systemctl start foo.service). Check the status to verify that the correct actions are taking place.