rhnget: 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
/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/rhnget - from package: mrepo

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