glsl-fs-loop: 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-loop - from package: piglit

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

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