orbit-name-server: 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/orbit-name-server - from package: ORBit

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

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