shield-purge: 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-purge - 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-purge - from package: libpam-shield

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

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