glxinfo: 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/bin/glxinfo - from package: glx-utils

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

On Debian possible default full paths are:

/usr/bin/glxinfo - from package: mesa-utils

You may install the required package with command apt-get install {package}

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