select-drbl-clients: 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/share/drbl/sbin/select-drbl-clients - from package: drbl

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

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