shield-trigger-iptables: 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/shield-trigger-iptables - from package: pam_shield

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

On Debian possible default full paths are:

/usr/sbin/shield-trigger-iptables - from package: libpam-shield

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

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