petri-foo: 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/petri-foo - from package: petri-foo

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

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