graph2tree: 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/graph2tree - from package: octomap

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

On Debian possible default full paths are:

/usr/bin/graph2tree - from package: octomap-tools

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

Error in other languages:
graph2tree: bevel nie gevind nie
graph2tree: comandă negăsită
graph2tree: comando não encontrado
graph2tree: commande introuvable
graph2tree: command not found
graph2tree: käsku ei ole
graph2tree: không tìm thấy lệnh
graph2tree: komanda nerasta
graph2tree: Kommando nicht gefunden.
graph2tree: kommandot finns inte
graph2tree: komut yok
graph2tree: nie znaleziono polecenia
graph2tree: níor aimsíodh an t-ordú
graph2tree: no se encontró la orden
graph2tree: no s'ha trobat l'ordre
graph2tree: opdracht niet gevonden
graph2tree: parancs nem található
graph2tree: perintah tidak ditemukan
graph2tree: príkaz nenájdený
graph2tree: příkaz nenalezen
graph2tree: команда не найдена
graph2tree: командата не е открита
graph2tree: 命令找不到
graph2tree: コマンドが見つかりません