glx-create-context-valid-flag-forward-compatible: 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-create-context-valid-flag-forward-compatible - from package: piglit

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

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