xfwm4-settings: 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-settings - from package: xfwm4

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

On Debian possible default full paths are:

/usr/bin/xfwm4-settings - from package: xfwm4

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

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