rdfgraphisomorphism: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/rdfgraphisomorphism - from package: python-rdflib-tools

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