xclipboard: 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/xclipboard - 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/xclipboard - from package: x11-apps

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

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