rhn-custom-info: 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/rhn-custom-info - from package: rhn-custom-info

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