ferret-browser: 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/ferret-browser - from package: ruby-ferret

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

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