rhnpush: 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/rhnpush - from package: rhnpush

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

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