metacity-window-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 CentOS possible default full paths are:

/usr/bin/metacity-window-demo - from package: metacity-devel

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

On Debian possible default full paths are:

/usr/bin/metacity-window-demo - from package: metacity

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

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