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 set for the service unit this command is called from.
Note that sd_notify() notifications may be attributed to units correctly only if either the sending process is still around at the time PID 1 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.
systemd-notify will first attempt to invoke sd_notify() pretending to have the PID of 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 described above.
The following options are understood:
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/bash mkfifo /tmp/waldo systemd-notify --ready --status="Waiting for data..." while : ; do read a < /tmp/waldo systemd-notify --status="Processing $a" # Do something with $a ... systemd-notify --status="Waiting for data..." done