darkplaces-glx: 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-glx - from package: darkplaces

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

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