glx-swap-event: 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/glx-swap-event - from package: piglit

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

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