silvia_proxy: 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:

/usr/bin/silvia_proxy - from package: silvia

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