drbl-client-system-select: 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/drbl-client-system-select - from package: drbl

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

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