graph.html: 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/doc/python-celery-doc/html/_modules/celery/bin/graph.html - from package: python-celery-doc

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

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