import_tracks: 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/import_tracks - from package: mrtrix

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

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