icinga2-build-key: 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/icinga2-build-key - from package: icinga2-common

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

Error in other languages:
icinga2-build-key: bevel nie gevind nie
icinga2-build-key: comandă negăsită
icinga2-build-key: comando não encontrado
icinga2-build-key: commande introuvable
icinga2-build-key: command not found
icinga2-build-key: käsku ei ole
icinga2-build-key: không tìm thấy lệnh
icinga2-build-key: komanda nerasta
icinga2-build-key: Kommando nicht gefunden.
icinga2-build-key: kommandot finns inte
icinga2-build-key: komut yok
icinga2-build-key: nie znaleziono polecenia
icinga2-build-key: níor aimsíodh an t-ordú
icinga2-build-key: no se encontró la orden
icinga2-build-key: no s'ha trobat l'ordre
icinga2-build-key: opdracht niet gevonden
icinga2-build-key: parancs nem található
icinga2-build-key: perintah tidak ditemukan
icinga2-build-key: príkaz nenájdený
icinga2-build-key: příkaz nenalezen
icinga2-build-key: команда не найдена
icinga2-build-key: командата не е открита
icinga2-build-key: 命令找不到
icinga2-build-key: コマンドが見つかりません