gpgkey2ssh: 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/gpgkey2ssh - from package: gnupg2

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

On Debian possible default full paths are:

/usr/bin/gpgkey2ssh - from package: gnupg-agent

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

Error in other languages:
gpgkey2ssh: bevel nie gevind nie
gpgkey2ssh: comandă negăsită
gpgkey2ssh: comando não encontrado
gpgkey2ssh: commande introuvable
gpgkey2ssh: command not found
gpgkey2ssh: käsku ei ole
gpgkey2ssh: không tìm thấy lệnh
gpgkey2ssh: komanda nerasta
gpgkey2ssh: Kommando nicht gefunden.
gpgkey2ssh: kommandot finns inte
gpgkey2ssh: komut yok
gpgkey2ssh: nie znaleziono polecenia
gpgkey2ssh: níor aimsíodh an t-ordú
gpgkey2ssh: no se encontró la orden
gpgkey2ssh: no s'ha trobat l'ordre
gpgkey2ssh: opdracht niet gevonden
gpgkey2ssh: parancs nem található
gpgkey2ssh: perintah tidak ditemukan
gpgkey2ssh: príkaz nenájdený
gpgkey2ssh: příkaz nenalezen
gpgkey2ssh: команда не найдена
gpgkey2ssh: командата не е открита
gpgkey2ssh: 命令找不到
gpgkey2ssh: コマンドが見つかりません