xrootd: 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 - from package: xrootd-server

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

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