clearbuffer-invalid-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/clearbuffer-invalid-buffer - from package: piglit

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

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