graph: 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 CentOS possible default full paths are:

/usr/bin/graph - from package: plotutils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/graph - from package: plotutils

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

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