qhull: 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/qhull - from package: qhull

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

On Debian possible default full paths are:

/usr/bin/qhull - from package: qhull-bin

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

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