xmlcatalog: 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/xmlcatalog - from package: libxml2

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

On Debian possible default full paths are:

/usr/bin/xmlcatalog - from package: libxml2-utils

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

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