strongswan: 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/strongswan - from package: strongswan

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

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