xfdesktop-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/xfdesktop-settings - from package: xfdesktop

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

On Debian possible default full paths are:

/usr/bin/xfdesktop-settings - from package: xfdesktop4

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

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