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

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

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