xrootd-3: 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/xrootd-3 - from package: xrootd-compat

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

Error in other languages:
xrootd-3: bevel nie gevind nie
xrootd-3: comandă negăsită
xrootd-3: comando não encontrado
xrootd-3: commande introuvable
xrootd-3: command not found
xrootd-3: käsku ei ole
xrootd-3: không tìm thấy lệnh
xrootd-3: komanda nerasta
xrootd-3: Kommando nicht gefunden.
xrootd-3: kommandot finns inte
xrootd-3: komut yok
xrootd-3: nie znaleziono polecenia
xrootd-3: níor aimsíodh an t-ordú
xrootd-3: no se encontró la orden
xrootd-3: no s'ha trobat l'ordre
xrootd-3: opdracht niet gevonden
xrootd-3: parancs nem található
xrootd-3: perintah tidak ditemukan
xrootd-3: príkaz nenájdený
xrootd-3: příkaz nenalezen
xrootd-3: команда не найдена
xrootd-3: командата не е открита
xrootd-3: 命令找不到
xrootd-3: コマンドが見つかりません