glsl-link-test: 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-link-test - from package: piglit

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

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