glsl-fs-flat-color: 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/glsl-fs-flat-color - from package: piglit

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

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