mkpasswd-ratbox: 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/sbin/mkpasswd-ratbox - from package: ircd-ratbox

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

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