{"id":14452,"date":"2017-10-22T23:26:39","date_gmt":"2017-10-23T03:26:39","guid":{"rendered":"http:\/\/scruss.com\/blog\/?p=14452"},"modified":"2017-10-22T23:44:40","modified_gmt":"2017-10-23T03:44:40","slug":"creating-a-systemd-user-service-on-your-raspberry-pi","status":"publish","type":"post","link":"https:\/\/scruss.com\/blog\/2017\/10\/22\/creating-a-systemd-user-service-on-your-raspberry-pi\/","title":{"rendered":"Creating a systemd user service on your Raspberry Pi"},"content":{"rendered":"

Flushed with success from yesterday’s post where I made my first systemd service<\/a>, I got carried away and wanted to show you how to create a service that runs as a regular user.<\/p>\n

A fairly common question on the Raspberry Pi Forums<\/a> is \u00e2\u20ac\u0153How do I run a script every time I reboot?\u00e2\u20ac\u009d. The traditional answer (and one I’ve given more than once) is to add a @reboot<\/strong> clause to your crontab. This will indeed run a command when the computer reboots, but it will run pretty early on in the boot sequence when there’s no guarantee of network or time services. So the usual remedy is a bit of a kludge:<\/p>\n

@reboot sleep 60 && <\/code>\u00e2\u20ac\u00a6<\/pre>\n
This waits a full minute after rebooting, then executes the command. Network and time services are really likely to be available, but it’s not very elegant. Cron also has some weird gotchas with PATH settings, so while it’s ubiquitous and has worked for decades, it’s not easy to get working. Systemd, however, has a much better way of doing it, and better yet, you can do it all without ever hitting sudo<\/strong>.<\/p>\n
I’ll take as a basis for this post the forum query \u00e2\u20ac\u0153python and crontab<\/a>\u00e2\u20ac\u009d. The asker wanted to log the time when their Raspberry Pi had rebooted, but they’ve hit the usual problem that the clock didn’t have the right time when their script was triggered, so the log was useless.<\/p>\n
(I’m not going to do exactly<\/em> what the forum poster did, but this is more a demo of a systemd user service than recreating their results.)<\/p>\n
First off, here’s the script to log the time to a file (saved as ~\/bin\/boot_time.py<\/code>):<\/p>\n
#!\/usr\/bin\/python3\r\nfrom time import strftime\r\nwith open(\"\/home\/pi\/logs\/boot_time.txt\", \"a\") as log:\r\n log.write(strftime(\"%d-%m-%Y,%H:%M:%S\\n\"))<\/pre>\n
I’d have done this as a shell script, but the OP used Python, so why fight it?<\/p>\n
FUN FACT<\/strong><\/span>: Under most<\/em> Linux flavours, if you create a\u00c2\u00a0bin<\/code> folder in your home directory, it’s automatically added to your path. So I could just type boot_time.py<\/code> and the shell would find it.
\n(You might have to log out and log back in again for the shell to review your path.)<\/p>\n
In order to get that to run, I need to do a little housekeeping: make the script executable, and make sure the\u00c2\u00a0logs<\/code> folder exits:<\/p>\n
chmod +x ~\/bin\/boot_time.py\r\nmkdir -p ~\/logs<\/pre>\n
Now we need to do the bits that pertain to systemd. First off, you must make a folder for user services:<\/p>\n
mkdir -p ~\/.config\/systemd\/user<\/pre>\n
NOTE<\/strong><\/span>: mkdir -p \u00e2\u20ac\u00a6<\/code> is useful here as it makes the directory and any parent directories that don’t exist. It also doesn’t complain if any of them already exist. It’s kind of a \u00e2\u20ac\u0153make sure this directory exists<\/em>\u00e2\u20ac\u009d command. Make friends with it.<\/p>\n
And here’s the service file, which I saved as ~\/.config\/systemd\/user\/boot_time_log.service<\/code>:<\/p>\n
[Unit]\r\nDescription=boot time log\r\nDefaultDependencies=no\r\nAfter=local-fs.target time-sync.target\r\n\r\n[Service]\r\nType=oneshot\r\nExecStart=\/home\/pi\/bin\/boot_time.py\r\n\r\n[Install]\r\nWantedBy=default.target<\/pre>\n
The service file does the following (even if I’m slightly mystified by some of the headings \u00e2\u20ac\u00a6):<\/p>\n