irelief-sigma: 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/irelief-sigma - from package: python-mlpy

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

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