Yesterday, I ran yum upgrade on the mini computer centos 7.5, which I just got. After restarting, I found that wifi can't connect to the Internet, so I studied it.

First, use the ip addr command to view the list of available network devices. If there is no wifi device, you can only see the lo device and two wired network cards:

[root@localhost ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp2s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether dc:9c:52:00:01:da brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.252/24 brd 192.168.3.255 scope global noprefixroute enp2s0
       valid_lft forever preferred_lft forever
    inet6 fe80::676f:d9f0:e14a:9e32/64 scope link tentative noprefixroute
       valid_lft forever preferred_lft forever
3: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether dc:9c:52:00:01:db brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.251/24 brd 192.168.3.255 scope global noprefixroute enp3s0
       valid_lft forever preferred_lft forever
    inet6 fe80::7289:760:7f85:7c19/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

Then I use lspci command to check the list of pci devices. I can see wifi devices

01:00.0 Network controller: Qualcomm Atheros QCA9377 802.11ac Wireless Network Adapter (rev 31)
02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 07)
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 07)

So it should be something wrong with the startup process.

Looking at the dmesg information, we found that the reading device encountered an error.. Replaced with the net chart in the related post)

So I searched the Internet for questions and finally found this post: linuxquestions.org solution_url
Basically, it means that new device firmware has been downloaded after yum upgrade, but there is a problem with this version of firmware. Therefore, you need to delete the firmware with the wrong version in the relevant directory and keep another firmware that can work.
This post mentions a more detailed discussion on the gentoo Forum gentoo discussion_url

The specific solution process is as follows:
Check whether there is any under the path / lib/firmware/ath10k/QCA9377/hw1.0 /
Firmware-5.bin and firmware-6.bin. If yes, delete firmware-6.bin and keep firmware-5.bin. Then restart the computer and the wifi device will work again.

In the post of this post on ps linuxquestion forum, some people specially registered their id to thank them, and others specially reset their forum password to say thank you (maybe they didn't post their password for a long time ago). The world is so beautiful~~