psk-crack: 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/bin/psk-crack - from package: ike-scan

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

On Debian possible default full paths are:

/usr/bin/psk-crack - from package: ike-scan

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

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