xrandr: 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/xrandr - 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/xrandr - from package: x11-xserver-utils

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

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