xdelta: 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/xdelta - from package: xdelta

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

On Debian possible default full paths are:

/usr/bin/xdelta - from package: xdelta

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

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