nettest: 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/nettest - from package: VirtualGL

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

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