backup: 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/backup - from package: openafs-client
/usr/share/solr/bin/backup - from package: solr-common
/usr/lib/wims/bin/backup - from package: wims

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

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