glxheads: 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 Debian possible default full paths are:

/usr/bin/glxheads - from package: mesa-utils

You may install the required package with command apt-get install {package}

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