oxygen-demo: 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/oxygen-demo - from package: kde-style-oxygen

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

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