tensor_metric: 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/tensor_metric - from package: mrtrix

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

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