I have two questions
Q1. I can execute the webpage now, but I get an error when I execute ./valudate.php.
[FAIL] Discovery has never run. Check the cron job
[root@localhost librenms]# ./validate.php
Component
Version
LibreNMS
1.43-134-g68484d3
DB Schema
268
PHP
7.2.10
MySQL
5.5.60-MariaDB
RRDTool
1.4.8
SNMP
NET-SNMP 5.7.2
=============================================
[OK] Composer Version: 1.7.2
[OK] Dependencies up-to-date.
[OK] Database connection successful
[OK] Database schema correct
[FAIL] Discovery has never run. Check the cron job
Q2. I am adding a device, there will be can not ping x.x.x.x
I confirm that I can ping it. What is the way?
Sounds like you didnt setup something right or your firewall on the server that libreNMS is running on.
Also from the install docs
Allow fping
Create the file http_fping.tt with the following contents. You can create this file anywhere, as it is a throw-away file. The last step in this install procedure will install the module in the proper location.