dipy_fit_tensor: 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/dipy_fit_tensor - from package: python-dipy

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

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