bup: 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/bin/bup - from package: bup

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

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