pd-gui: 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/pd-gui - from package: puredata-gui

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

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