pki: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

/usr/bin/pki - from package: strongswan-starter

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