install_packages: 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/sbin/install_packages - from package: fai-client

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

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