@Chadmon10 said in Retropie won't boot into a rom, tries, then goes to command line.:
/opt/retropie/supplementary/runcommand/runcommand.sh 0 _SYS_ megadrive "/RetroPie/roms/megadrive/Sonic The Hedgehog 2 (World).md"
You forgot the ~ in ~/RetroPie/roms/megadrive/Sonic The Hedgehog 2 (World).md.