To permanently turn on line numbers in IntelliJ IDEA (and other JetBrains IDEs):

1. Go to File > Settings…
2. Then go to Editor > General > Appearance.
3. Check the Show line numbers box.
4. Click Apply and OK.
5. Line numbers are now permanently turned on.

IntelliJ 14.X Onwards

From version 14.0 onwards, the path to the setting dialog is slightly different, a General submenu has been added between Editor and Appearance as shown below

IntelliJ 8.1.2 – 13.X

From IntelliJ 8.1.2 onwards, this option is in File | Settings1. Within the IDE Settings section of that dialog

• On a Mac, these are named IntelliJ IDEA | Preferences

In  IJ 13

1. Press shift+shift
2. Type “line number”
3. The option shows in the menu and press enter to enable/disable.

There’s another way,

• Simply right click on the place where the line-numbers should be, and there you’ll see a small menu.
• then, mark the “Show Line Numbers” option.
• Note that this only works on a per-file basis

In Intellij 13 the layout has changed, the Settings button can only be found in File -> Settings and not in the toolbars, and from there you follow the same steps: Editor -> Appearance -> Show line numbers, or search for Line numbers in the Settings search input.

For InteliJ IDEA 11.0 and above

Goto File –> Settings in the Settings window Editor –> Appearance
and tick Show line numbers check box.

IntelliJ 14 (Ubuntu):

File > Settings > Editor > General > Appearance > show line numbers

For current Editor:

View > Active Editor > Show Line Numbers

In intelliJ 14 Ultimate using the Mac version this is it.

IntelliJ Idea > Preferences > Editor > General > Appearance > Show Line Numbers