ckeygen: 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/ckeygen - from package: python-twisted-conch

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

On Debian possible default full paths are:

/usr/bin/ckeygen - from package: python-twisted-conch

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

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