Since Ubuntu 14.04, the mouse pointer tracking speed can no longer be adjusted in System Settings. Here’s how to set your own speed and let it persist across sessions.
1. Open Terminal
2. Type the command
xset m acceleration threshold
Acceleration is basically how fast you want the cursor to move.
Threshold, according to the Arch Linux Wiki, “defines the point at which acceleration should occur in pixels per 10 ms”. For example, if threshold=5, then the pointer will get a boost in travel distance when moved at speeds over 5 pixels per 10 milliseconds.
I use “xset m 2 1”. Try that as an example. Your settings will vary according to the sensitivity of the mouse itself and your personal preference, so experiment with different values in Terminal until you find your favorite configuration.
3. In order to make the settings stick after reboot, open the Startup Applications app (search for it in the Launcher).
4. Click “Add“.
5. Name it something like “Mouse Speed”.
6. Type in the command we just came up with in the “Command” text box.