tar-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/tar-backup - from package: tar-scripts

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

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