xfwm4: 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/xfwm4 - from package: xfwm4

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

On Debian possible default full paths are:

/usr/bin/xfwm4 - from package: xfwm4

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

Error in other languages:
xfwm4: bevel nie gevind nie
xfwm4: comandă negăsită
xfwm4: comando não encontrado
xfwm4: commande introuvable
xfwm4: command not found
xfwm4: käsku ei ole
xfwm4: không tìm thấy lệnh
xfwm4: komanda nerasta
xfwm4: Kommando nicht gefunden.
xfwm4: kommandot finns inte
xfwm4: komut yok
xfwm4: nie znaleziono polecenia
xfwm4: níor aimsíodh an t-ordú
xfwm4: no se encontró la orden
xfwm4: no s'ha trobat l'ordre
xfwm4: opdracht niet gevonden
xfwm4: parancs nem található
xfwm4: perintah tidak ditemukan
xfwm4: príkaz nenájdený
xfwm4: příkaz nenalezen
xfwm4: команда не найдена
xfwm4: командата не е открита
xfwm4: 命令找不到
xfwm4: コマンドが見つかりません