clearbuffer-invalid-drawbuffer: 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-drawbuffer - from package: piglit

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

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