glsl-cos: command not found

Have You tried accessing the binary with the full path?

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-cos - from package: piglit

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