mkfs.jffs2: 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/mkfs.jffs2 - from package: mtd-utils

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

Error in other languages:
mkfs.jffs2: bevel nie gevind nie
mkfs.jffs2: comandă negăsită
mkfs.jffs2: comando não encontrado
mkfs.jffs2: commande introuvable
mkfs.jffs2: command not found
mkfs.jffs2: käsku ei ole
mkfs.jffs2: không tìm thấy lệnh
mkfs.jffs2: komanda nerasta
mkfs.jffs2: Kommando nicht gefunden.
mkfs.jffs2: kommandot finns inte
mkfs.jffs2: komut yok
mkfs.jffs2: nie znaleziono polecenia
mkfs.jffs2: níor aimsíodh an t-ordú
mkfs.jffs2: no se encontró la orden
mkfs.jffs2: no s'ha trobat l'ordre
mkfs.jffs2: opdracht niet gevonden
mkfs.jffs2: parancs nem található
mkfs.jffs2: perintah tidak ditemukan
mkfs.jffs2: príkaz nenájdený
mkfs.jffs2: příkaz nenalezen
mkfs.jffs2: команда не найдена
mkfs.jffs2: командата не е открита
mkfs.jffs2: 命令找不到
mkfs.jffs2: コマンドが見つかりません