dipy_peak_extraction: 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_peak_extraction - from package: python-dipy

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

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