checkrad: 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/sbin/checkrad - from package: freeradius

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

On Debian possible default full paths are:

/usr/sbin/checkrad - from package: freeradius

You may install the required package with command apt-get install {package}

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