rskeygen: 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 Debian possible default full paths are:

/usr/bin/rskeygen - from package: rabbitsign

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

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