vglclient: 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/vglclient - from package: VirtualGL

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

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