rsf2cnf: 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/rsf2cnf - from package: undertaker

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

Error in other languages:
rsf2cnf: bevel nie gevind nie
rsf2cnf: comandă negăsită
rsf2cnf: comando não encontrado
rsf2cnf: commande introuvable
rsf2cnf: command not found
rsf2cnf: käsku ei ole
rsf2cnf: không tìm thấy lệnh
rsf2cnf: komanda nerasta
rsf2cnf: Kommando nicht gefunden.
rsf2cnf: kommandot finns inte
rsf2cnf: komut yok
rsf2cnf: nie znaleziono polecenia
rsf2cnf: níor aimsíodh an t-ordú
rsf2cnf: no se encontró la orden
rsf2cnf: no s'ha trobat l'ordre
rsf2cnf: opdracht niet gevonden
rsf2cnf: parancs nem található
rsf2cnf: perintah tidak ditemukan
rsf2cnf: príkaz nenájdený
rsf2cnf: příkaz nenalezen
rsf2cnf: команда не найдена
rsf2cnf: командата не е открита
rsf2cnf: 命令找不到
rsf2cnf: コマンドが見つかりません