ruby2gv: 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/ruby2gv - from package: ruby-graphviz

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

Error in other languages:
ruby2gv: bevel nie gevind nie
ruby2gv: comandă negăsită
ruby2gv: comando não encontrado
ruby2gv: commande introuvable
ruby2gv: command not found
ruby2gv: käsku ei ole
ruby2gv: không tìm thấy lệnh
ruby2gv: komanda nerasta
ruby2gv: Kommando nicht gefunden.
ruby2gv: kommandot finns inte
ruby2gv: komut yok
ruby2gv: nie znaleziono polecenia
ruby2gv: níor aimsíodh an t-ordú
ruby2gv: no se encontró la orden
ruby2gv: no s'ha trobat l'ordre
ruby2gv: opdracht niet gevonden
ruby2gv: parancs nem található
ruby2gv: perintah tidak ditemukan
ruby2gv: príkaz nenájdený
ruby2gv: příkaz nenalezen
ruby2gv: команда не найдена
ruby2gv: командата не е открита
ruby2gv: 命令找不到
ruby2gv: コマンドが見つかりません