Now that I finally created my tarsnap backup script, how do I execute it regularly? Oh, I know: My Mac is just an Unix system, I’ll use cron!
At least that’s what I thought I’ll do. After a few attempts to get cron to do the job, I learned that there’s a better way on macOS: launchd.
At it’s core, launchd distincts daemons and agents. Dameons are processes that always run in the background, while agents describe regular jobs that are to be executed on certain events. There are a lot of different events to choose from. For example you can trigger an agent, when a device gets mounted, when a file gets created, or when a certain time arrives.
What really helped me in learning how to write my first launchd agent was
launchd.info. Unlike the Apple
it contains useful snippets and concise explanations. I highly recommend that
you also have a look at the launchd agents that some of your applications put into
Below you can see the agent that I ended up creating. You can learn how to load/unload agents and about the meaning of the different options at launchd.info.
If you’re testing your script and you don’t want to wait for the next hour to
arrive, you can start it immediately with
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>Label</key> <string>eu.jan-ahrens.tarsnap</string> <key>EnvironmentVariables</key> <dict> <key>PATH</key> <string>/bin:/usr/bin:/usr/local/bin</string> </dict> <key>ProgramArguments</key> <array> <string>/bin/bash</string> <string>/Users/jan/bin/run-tarsnap-backup</string> </array> <key>StartInterval</key> <integer>3600</integer> <key>StandardOutPath</key> <string>/Users/jan/.tarsnap.log</string> <key>StandardErrorPath</key> <string>/Users/jan/.tarsnap.log</string> <key>KeepAlive</key> <dict> <key>NetworkState</key> <true/> </dict> <key>ExitTimeout</key> <integer>900</integer> <key>Nice</key> <integer>10</integer> </dict> </plist>
P.S.: cron itself is implemented as a launchd daemon. You can find it at