novnc_server: 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/novnc_server - from package: novnc

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

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