grpunconv: 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/grpunconv - from package: shadow-utils

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

On Debian possible default full paths are:

/usr/sbin/grpunconv - from package: passwd

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

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