arb_color_buffer_float-readpixels: 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/arb_color_buffer_float-readpixels - from package: piglit

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

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