ngraph: 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/ngraph - from package: ngraph-gtk

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

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