xrefresh: 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/xrefresh - from package: xorg-x11-server-utils

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

On Debian possible default full paths are:

/usr/bin/xrefresh - from package: x11-xserver-utils

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

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