After Linux is installed on your SSD, don’t forget to enable the Discard operation, to let your SSD know which blocks are free to be reclaimed.

Checking the trim support

In order to check that the SSD properly supports the discard command, run

$ lsblk --discard
NAME   DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sdc           0        4K       4G         0
├─sdc1        0        4K       4G         0
└─sdc2        0        4K       4G         0

If the DISC-GRAN and DISC-MAX are non-zero, discard is supported for that particular drive.

However, that’s not enough. You must make sure to check that trim is supported for the block device hosting your root filesystem (and possibly other filesystems, e.g. /home etc). See tips below for enabling trim all the way for the most common cases.

If you have installed your Linux into a LVM, then you need to configure LVM to pass-through the Discard operation. Edit /etc/lvm/lvm.conf and make sure the devices{} section contains issue_discards = 1.

Alternatively if you’re using dm-crypt, edit /etc/crypttab and make sure the discard option is there.

Finally, you need to enable discard for all of your ext4 partitions: simply add the discard option to /etc/fstab. Note that swap on a swap partition will perform discard automatically.

Please see the excellent SSD Optimization article for more details.

Running trim manually

Simply run the sudo fstrim -a command which will trim all unused blocks on all mounted filesystems. It is safe to run the command on a running Linux machine since the command is designed to run on live filesystems.

On Ubuntu the command is scheduled to be run every week: read Is TRIM enabled on my Ubuntu 18.04 installation? for more info. Run

$ journalctl -u fstrim.service

to check that the trim was run on your machine.