arb-xfb-before-flatshading: 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-xfb-before-flatshading - from package: piglit

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

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