This works with Linux and Windows so it's all great
When in Linux, a lower resolution will cause my laptop screen to have a small screen in the middle and some "nice" black borders.
Since I use 1920x1200 as my native resolution and this isn't listed, I could live with this inconvenience or deal with it >
REMEMBER: It's always best to use the SAME resolution as your windows desktop, it ensures less problems with the games and often quite good FPS.
Anyway. If you can't find that resolution you use on the list. Open the terminal and do the following:
/set r_mode -1 #this will avoid the game from using a set mode, meaning one of the predefined resolutions shown in the options menu
With the custom mode unlocked, it's time to set a resolution, remember that a resolution is defined as WIDTHxHEIGHT, don't get it the wrong way around of the game may refuse to show anything (I'm not about to test this).
In my case, I wanted to use my 1920x1200 resolution, so i did:
/seta r_customWidth 1920
/seta r_customHeight 1200
After this, you may see messages saying that the resolution change will be applied upon game restart, if you want it straight away, just type:
/vid_restart
And boom! The game will reload the map but you'll retain any points/credits/whatever and be able to play in that good resolution
Just a short quickie, this tip is applicable to any and every Q3-based game so if its a general problem in Q3 games, don't be shy
About the set versus seta, it's NOT a typo. Basicly you can use set to set a variable for this session only. If you restart the game, the set variable will be gone, seta values are kept "for ever" (meaning until you change em').
Lastly, this game is great
