radsniff: 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/radsniff - from package: freeradius-utils

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

On Debian possible default full paths are:

/usr/bin/radsniff - from package: freeradius-utils

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

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