median3D: 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/lib/mrtrix/bin/median3D - from package: mrtrix

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

Error in other languages:
median3D: bevel nie gevind nie
median3D: comandă negăsită
median3D: comando não encontrado
median3D: commande introuvable
median3D: command not found
median3D: käsku ei ole
median3D: không tìm thấy lệnh
median3D: komanda nerasta
median3D: Kommando nicht gefunden.
median3D: kommandot finns inte
median3D: komut yok
median3D: nie znaleziono polecenia
median3D: níor aimsíodh an t-ordú
median3D: no se encontró la orden
median3D: no s'ha trobat l'ordre
median3D: opdracht niet gevonden
median3D: parancs nem található
median3D: perintah tidak ditemukan
median3D: príkaz nenájdený
median3D: příkaz nenalezen
median3D: команда не найдена
median3D: командата не е открита
median3D: 命令找不到
median3D: コマンドが見つかりません