OCS Inventory doesn't show any devices

Affter installing OCS Inventory Server 2.4 on Ubunu 18.04, I could run OCS throught http://localhost/ocsreports. But in the main page, it could not scan any devices currently connected my LAN. I tried to use SNMP and IPDiscover function (in the Networks tab) but in vain.

And I had installed OCS Inventory NG Agent in another windows's pc, but it seems not working. Here it's log

==============================================================================

Starting OCS Inventory NG Agent on Tuesday, July 31, 2018 10:56:24.

AGENT => Running OCS Inventory NG Agent Version 2.3.1.1

AGENT => Using OCS Inventory NG FrameWork Version 2.3.1.1

AGENT => Loading plug-in(s)

DLL PLUGIN => Searching for Plug-in DLL(s) in folder <C:\Program Files (x86)\OCS Inventory Agent\plugins>

DLL PLUGIN => 0 DLL Plug-in(s) successfully loaded on 0 DLL(s) found

AGENT => Using network connection with Communication Server

COM PROVIDER => Loading Communication Provider <C:\Program Files (x86)\OCS Inventory Agent\ComHTTP.dll>

AGENT => Using Communication Provider <OCS Inventory NG cURL Communication Provider> Version <2.3.1.1>

AGENT => Sending Prolog

DID_CHECK => Read DeviceID <IT-ADMIN-2018-07-28-11-12-52> and MACs <78:24:AF:36:E2:C420:41:53:59:4E:FF00:00:00:00:00:0000:00:00:00:00:00> in file <ocsinventory.dat>

DID_CHECK => writing DeviceID <IT-ADMIN-2018-07-28-11-12-52> and MACs <78:24:AF:36:E2:C400:00:00:00:00:0000:00:00:00:00:00> in file <C:\ProgramData\OCS Inventory NG\Agent\ocsinventory.dat>

COM SERVER => Initializing cURL library for sendRequest

COM SERVER => Using cURL with server authentication

COM SERVER => Disabling cURL proxy support

COM SERVER => Enabling cURL SSL server validation support using CA Bundle <C:\ProgramData\OCS Inventory NG\Agent\cacert.pem>

COM SERVER => Sending HTTP Post request to URL <http://192.168.1.127/ocsreports>

COM SERVER => HTTP Post response received <HTTP Status Code #200>

COM SERVER => Cleaning cURL library

AGENT => Prolog successfully sent

AGENT => Prolog Frequency set to 10 hour(s)

AGENT => Inventory on startup option set to
AGENT => Unloading communication provider

AGENT => Unloading plug-in(s)

AGENT => Execution duration: 00:00:00.

Could someone help me pls?