xdmx: 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/xdmx - from package: xorg-x11-server-Xdmx

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

On Debian possible default full paths are:

/usr/bin/xdmx - from package: xdmx

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

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