zbackup: 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/bin/zbackup - from package: zbackup

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

On Debian possible default full paths are:

/usr/bin/zbackup - from package: zbackup

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

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