radvd: 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/radvd - from package: radvd

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

On Debian possible default full paths are:

/usr/sbin/radvd - from package: radvd

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

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