occlusion-query-discard: 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/lib64/piglit/bin/occlusion-query-discard - from package: piglit

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

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