unshadow: 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/unshadow - from package: john

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

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