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Mule is a simple tool to launch a program in different directories and pass
signals to the created children processes. It can be used to run an application
which exists in several versions.

Imagine versions of SuperApp are deployed in /var/superapp/VERSION/bin/superapp
with their respective configuration file in /var/superapp/VERSION/config.json.
You can run all the versions by calling:

$ mule /var/superapp bin/superapp config.json

To send, say, SIGINT to all processes, send it to the Mule process.

At the moment, Mule passes the following signals:

* SIGTERM
* SIGQUIT
* SIGINT
* SIGHUP

# Options

To run the program with specified user and group, use -u or --user and
-g or --group. To detach the process, use -b or --backgound. Finally, -n or
--name overwrites the name of the program.

These options are useful when using Mule in a rc script or similar. Remember
that rc.subr is sending SIGKILL to the processes which cannot be caught. You
would need to write a slightly more complex script with something like the
following code. See rc.subr(8).

#!/bin/sh

daemon="/usr/local/bin/mule -u www -g www -n mule-superapp -b \
        /var/superapp bin/superapp config.json"

. /etc/rc.d/rc.subr

pexp="mule-superapp"

rc_reload=NO

rc_stop() {
    pkill -SIGTERM -f "^${pexp}"
    (pkill -0 -f "^${pexp}" && sleep 1 && pkill -SIGKILL -f "^${pexp}") || true
    if pkill -0 -f "^${pexp}"; then
        exit 1
    fi
}

rc_cmd $1