mrview: 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/mrview - from package: mrtrix
/usr/lib/mrtrix/bin/mrview - from package: mrtrix

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

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