rad_counter: 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/rad_counter - from package: freeradius-utils

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

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