backupninja: 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/backupninja - from package: backupninja

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

On Debian possible default full paths are:

/usr/sbin/backupninja - from package: backupninja

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

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