qhalf: 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/qhalf - from package: qhull

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

On Debian possible default full paths are:

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

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

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