cobbler-ext-nodes: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/cobbler-ext-nodes - from package: cobbler

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