systemd-notify - Notify service manager about start-up completion and other daemon status changes
systemd-notify may be called by service scripts to notify the invoking service manager about status changes. It can be used to send arbitrary information, encoded in an environment-block-like list of strings. Most importantly, it can be used for start-up completion notification.
This is mostly just a wrapper around sd_notify() and makes this functionality available to shell scripts. For details see sd_notify(3).
The command line may carry a list of environment variables to send as part of the status update.
Note that systemd will refuse reception of status updates from this command unless NotifyAccess= is appropriately set for the service unit this command is called from. See systemd.service(5) for details.
Note that sd_notify() notifications may be attributed to units correctly only if either the sending process is still around at the time the service manager processes the message, or if the sending process is explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked off the process, i.e. on all processes that match NotifyAccess=main or NotifyAccess=exec. Conversely, if an auxiliary process of the unit sends an sd_notify() message and immediately exits, the service manager might not be able to properly attribute the message to the unit, and thus will ignore it, even if NotifyAccess=all is set for it. To address this systemd-notify will wait until the notification message has been processed by the service manager. When --no-block is used, this synchronization for reception of notifications is disabled, and hence the aforementioned race may occur if the invoking process is not the service manager or spawned by the service manager.
systemd-notify will first attempt to invoke sd_notify() pretending to have the PID of the parent process of systemd-notify (i.e. the invoking process). This will only succeed when invoked with sufficient privileges. On failure, it will then fall back to invoking it under its own PID. This behaviour is useful in order that when the tool is invoked from a shell script the shell process — and not the systemd-notify process — appears as sender of the message, which in turn is helpful if the shell process is the main process of a service, due to the limitations of NotifyAccess=all. Use the --pid= switch to tweak this behaviour.
The following options are understood:
If this switch is used in an systemd-notify invocation from a process that shall become the new main process of a service — and which is not the process forked off by the service manager (or the current main process) —, then it is essential to set NotifyAccess=all in the service unit file, or otherwise the notification will be ignored for security reasons. See systemd.service(5) for details.
On success, 0 is returned, a non-zero failure code otherwise.
Example 1. Start-up Notification and Status Updates
A simple shell daemon that sends start-up notifications after having set up its communication channel. During runtime it sends further status updates to the init system:
#!/bin/sh mkfifo /tmp/waldo systemd-notify --ready --status="Waiting for data..." while : ; do
read -r a < /tmp/waldo
systemd-notify --status="Processing $a"
# Do something with $a ...
systemd-notify --status="Waiting for data..." done
systemd(1), systemctl(1), systemd.unit(5), systemd.service(5), sd_notify(3), sd_booted(3)