unshunt: 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/lib/mailman/bin/unshunt - from package: mailman

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

On Debian possible default full paths are:

/usr/lib/mailman/bin/unshunt - from package: mailman

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

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