system-tools-backends: 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/system-tools-backends - from package: system-tools-backends

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

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