mkfs.reiser4: 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:

/sbin/mkfs.reiser4 - from package: reiser4progs

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

Error in other languages:
mkfs.reiser4: bevel nie gevind nie
mkfs.reiser4: comandă negăsită
mkfs.reiser4: comando não encontrado
mkfs.reiser4: commande introuvable
mkfs.reiser4: command not found
mkfs.reiser4: käsku ei ole
mkfs.reiser4: không tìm thấy lệnh
mkfs.reiser4: komanda nerasta
mkfs.reiser4: Kommando nicht gefunden.
mkfs.reiser4: kommandot finns inte
mkfs.reiser4: komut yok
mkfs.reiser4: nie znaleziono polecenia
mkfs.reiser4: níor aimsíodh an t-ordú
mkfs.reiser4: no se encontró la orden
mkfs.reiser4: no s'ha trobat l'ordre
mkfs.reiser4: opdracht niet gevonden
mkfs.reiser4: parancs nem található
mkfs.reiser4: perintah tidak ditemukan
mkfs.reiser4: príkaz nenájdený
mkfs.reiser4: příkaz nenalezen
mkfs.reiser4: команда не найдена
mkfs.reiser4: командата не е открита
mkfs.reiser4: 命令找不到
mkfs.reiser4: コマンドが見つかりません