rdisc: 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:

/sbin/rdisc - from package: iputils

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