glx-copy-sub-buffer: 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-copy-sub-buffer - from package: piglit

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

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