checkXML: 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/checkXML - from package: kdelibs

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

On Debian possible default full paths are:

/usr/bin/checkXML - from package: kdelibs5-dev

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

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