xwd: 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/xwd - from package: xorg-x11-apps

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

On Debian possible default full paths are:

/usr/bin/xwd - from package: x11-apps

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

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