Checkpoint64 has a preset for Garry's Mod: it already knows where the config folder is, backs it up automatically and keeps every version. Everything this site has on Garry's Mod:
Garry's Mod
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Config file location
Windows:
C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\cfg -
Backup guide
Competitive games keep your progress on their servers — what's on your disk is the config. Checkpoint64 versions the settings folder for 67 games and 16 dedicated servers, so a reinstall or a file verification can't cost you your binds. Free download.
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Server ports
UDP 27015 -
Launch options
-noaddons-noworkshop-console