feat(posts): Add post on fstrim + systemd

posts/2016-07-30-fstrim-systemd.md

+---
+title: Automatically TRIM-ing your SSD using systemd
+date: Sun Jul 30 17:34:50 UTC 2016
+author: Eduardo Trujillo
+uuid: ac1f6bf6-72be-4729-a545-6d6b08112149
+---
+
+If you have a Linux laptop or desktop with a solid-state drive, and happen to
+have disk encryption enabled through a LUKS/LVM combo, getting [TRIM][1]
+support enabled isn't a very straightforward process. It has to be enabled on
+every IO layer.
+
+In their blog post, [_How to properly activate TRIM for your SSD on Linux:
+fstrim, lvm and dm-crypt_][2], Carlos Lopez gives a brief introduction on what
+TRIM is, and explains why it is beneficial to enable it. The article also
+describes the steps needed to enable this functionality on each IO layer
+(dm-crypt, LVM, and the filesystem).
+
+I followed most of this guide for one my own systems, and while I followed
+their advice and avoided enabling the discard flag on the filesystem, I never
+set up a cron job for running the trim operation periodically. So I found
+myself manually executing [`fstrim`][3] every now and then by hand.
+
+This quickly became slightly repetitive, so I began looking into setting up the
+automation part. The guide above had an example setup using cron. However, I
+never set up a cron daemon on my system. So I wondered if it was possible to
+achieve the same result using systemd.
+
+After reading some documentation on systemd unit files, I learned that is
+possible to setup timers for your service units, which effectively achieves the
+same result as a cron daemon.
+
+Below I'm including a fstrim service and timer. The service mainly specifies
+which command to run and the timer defines how often it should be executed.
+Note that the service unit does not have a `WantedBy` option and its `Type` is
+`oneshot`. This means it won't be automatically executed, and that it is
+intended to be a one off command, not a daemon. The timer does have a
+`WantedBy` option, which will result on it being started at boot.
+
+I can check the status of the timer by using `systemctl list-times` and also
+run the operation on demands by starting the service unit: `systemctl start
+fstrim`. The logs are stored on the journal, which can be queried with
+`journalctl -u fstrim`.
+
+##### /etc/systemd/system/fstrim.service
+
+This is the service file. Here you can customize how `fstrim` is invoked. I use
+the `a` and `v` options, which tell `fstrim` to automatically run on every
+drive and print verbose output. Additionally, this assumes `fstrim` is
+installed at `/sbin/fstrim`.
+
+``` {#fstrimservice .ini}
+[Unit]
+Description=Run fstrim on all drives
+
+[Service]
+Type=oneshot
+ExecStart=/sbin/fstrim -av
+User=root
+```
+
+##### /etc/systemd/system/fstrim.timer
+
+In this configuration, the `fstrim` command is executed by `root` 15 minutes
+after booting the machine and weekly afterwards.
+
+``` {#fstrimtimer .ini}
+[Unit] Description=Run fstrim on boot and weekly afterwards
+
+[Timer]
+OnBootSec=15min
+OnUnitActiveSec=1w 
+
+[Install]
+WantedBy=timers.target
+```
+
+[1]: https://en.wikipedia.org/wiki/Trim_(computing)
+[2]: http://blog.neutrino.es/2013/howto-properly-activate-trim-for-your-ssd-on-linux-fstrim-lvm-and-dmcrypt/
+[3]: https://packages.gentoo.org/packages/sys-apps/util-linux