install_ferret_links: 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/share/ferret-vis/bin/install_ferret_links - from package: ferret-vis

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

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