icinga2-build-ca: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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-ca - from package: icinga2-common

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