pwunconv: 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 CentOS possible default full paths are:

/usr/sbin/pwunconv - from package: shadow-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/pwunconv - from package: passwd

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

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