ring: 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 Debian possible default full paths are:

/usr/bin/ring - from package: alliance

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

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