darkplaces-sdl: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/darkplaces-sdl - from package: darkplaces

You may install the required package with command yum install {package}

Error in other languages:
darkplaces-sdl: bevel nie gevind nie
darkplaces-sdl: comandă negăsită
darkplaces-sdl: comando não encontrado
darkplaces-sdl: commande introuvable
darkplaces-sdl: command not found
darkplaces-sdl: käsku ei ole
darkplaces-sdl: không tìm thấy lệnh
darkplaces-sdl: komanda nerasta
darkplaces-sdl: Kommando nicht gefunden.
darkplaces-sdl: kommandot finns inte
darkplaces-sdl: komut yok
darkplaces-sdl: nie znaleziono polecenia
darkplaces-sdl: níor aimsíodh an t-ordú
darkplaces-sdl: no se encontró la orden
darkplaces-sdl: no s'ha trobat l'ordre
darkplaces-sdl: opdracht niet gevonden
darkplaces-sdl: parancs nem található
darkplaces-sdl: perintah tidak ditemukan
darkplaces-sdl: príkaz nenájdený
darkplaces-sdl: příkaz nenalezen
darkplaces-sdl: команда не найдена
darkplaces-sdl: командата не е открита
darkplaces-sdl: 命令找不到
darkplaces-sdl: コマンドが見つかりません