Ubuntu 14.10 onwards

In Ubuntu 14.10 and 15.04, TRIMming happens automatically every week on all SSDs supported by fstrim.

$ tail -n1 /etc/cron.weekly/fstrim 
/sbin/fstrim --all || true

Since 15.04 Ubuntu uses systemd and its timer (man systemd.timer, Arch wiki)

systemctl list-timers
systemctl status fstrim.timer

Ubuntu 14.04

As of Ubuntu 14.04, scheduled TRIM is enabled by default for Intel, SAMSUNG, OCZ, Patriot and Sandisk SSDs. If you have another brand, you could disable the vendor check by running the following command:

sed -i 's/exec fstrim-all/exec fstrim-all --no-model-check/g' /etc/cron.weekly/fstrim

(or just edit the file /etc/cron.weekly/fstrim and add --no-model-check)

Ubuntu 13.10 and Earlier

There are three ways to perform TRIM, manual, scheduled, and automatic:

Manual TRIM

In Ubuntu this can be performed with fstrim:

sudo fstrim /

however it is not needed when scheduled or automatic TRIM are enabled, as detailed in the sections below.

Note: For Ubuntu 11.04 and earlier systems, fstrim is not available so you have to use wiper.sh supplied with hdparm in /usr/share/doc/hdparm/contrib/wiper.sh.gz

Scheduled TRIM (Recommended)

This is the currently recomended method, and is planed to be activated per default for Ubuntu 14.04. Here's how to activate it manually in older versions of ubuntu (11.10 to 13.10):

Create a weekly CRON job script file:

gksudo gedit /etc/cron.weekly/fstrim

Paste the following code in the file, then save and close the file:

#! /bin/sh  

# By default we assume only / is on an SSD. 
# You can add more SSD mount points, separated by spaces.
# Make sure all mount points are within the quotes. For example:
# SSD_MOUNT_POINTS='/ /boot /home /media/my_other_ssd'  

SSD_MOUNT_POINTS='/'  

for mount_point in $SSD_MOUNT_POINTS
do  
    fstrim $mount_point  
done

Note that the above assumes that only your root filesystem / is located on an SSD. If you have more mount points that reside on one or more SSDs, add them to SSD_MOUNT_POINTS as explained in the code.

Make the script executable:

sudo chmod +x /etc/cron.weekly/fstrim

And finally test it:

sudo /etc/cron.weekly/fstrim

If you see no errors, your cron job should be working fine.

Automatic TRIM (Deprecated, Slow)

Automatic TRIM has been supported since Ubuntu 10.10 (kernel 2.6.33) with the EXT4 file system. However, sending TRIM commands to the SSD in real-time - after every delete - has been recognized to make deletion much slower than usual on some drives. Therefore a weekly scheduled TRIM via a cron job (described above) is recomended.

To enable automatic TRIM on a drive or partition, they need to be mounted with the discard option in fstab. Firstly backup your fstab then open it for editing:

sudo cp /etc/fstab ~/fstab-backup
gksudo gedit /etc/fstab

Add discard to the fstab options entry (comma separated) for the SSD drive or each partition.

UUID=00000000-0000-0000-0000-000000000000  /  ext4  discard,errors=remount-ro  0  1

Close and save fstab, then reboot and automatic TRIM should now be working.

Testing automatic TRIM

To test if TRIM is working issue the following commands (source):

cd  / # Replace with SSD file system
sudo dd if=/dev/urandom of=tempfile count=100 bs=512k oflag=direct
sudo hdparm --fibmap tempfile

From the output copy the number under begin_LBA and verify the device name of your SSD: System->Administration->Disk Utility e.g. sda, sdb, sdc ...

Run the following but replace [ADDRESS] (begin_LBA) and sdX (SSD device name) with the details obtained above.

sudo hdparm --read-sector [ADDRESS] /dev/sdX 

the output should be a long string of characters for those sectors

sudo rm tempfile
sync

Repeat the hdparm command from above:

sudo hdparm --read-sector [ADDRESS] /dev/sdX 

If you get only zeros then automatic TRIM is working. However if after removing the file the sectors are still not empty then wait a while and run the command again.