backup-manager: 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 CentOS possible default full paths are:

/usr/sbin/backup-manager - from package: backup-manager

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/backup-manager - from package: backup-manager

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

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