# File to be place under /etc/NetworkManager/conf.d [connection]This didn't seem to do anything, as expected. The next thing I tried was a kernel setting. These particular usb wifi adapters were pretty popular for the raspberry pi a few years ago, and they had the exact problem I've been having. I followed these instructions (link) to create a 8192cu.conf file in /etc/modprobe.d/ with the following lines:
# Values are 0 (use default), 1 (ignore/don't touch), 2 (disable) or 3 (enable).
wifi.powersave = 2
# prevent power down of wireless when idleI then unloaded and loaded the driver using rmmod rtl8192cu and modprobe rtl8192cu. Besides that, I and google seem to be completely out of ideas. Update (a few months later): this usb adapter finally died on me. May have gotten a bad one, which could account for the above problems.
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0
I purchased a TP-Link TL-WN722N wifi usb adapter because a lot of people said it works well with Linux. It works without doing anything in Ubuntu 18.04, but it does not work well with CentOS. lsusb sees a device, but there aren't any compatible drivers installed. This particular one has a "V2" next to the FCC ID, but a "V3" in the serial number box. I tried downloading both V3 and the V2 linux drivers from TP-Link and compiling them, but they won't compile due to what looks like various syntax or coding errors. CentOS7.5's kernel version is within the supported range, so that's not the problem. I tried a bunch of fixes from google, including some sort of kernel driver firmware htc thing and a elrepo kmod package, but neither worked because I think they're only for the V1 version. I ended up giving up on it.
There are very few USB wifi adapters that will actually work with CentOS. Aside from the partially working Edimax one and thinkpenguin ones, I haven't found any others.
I also tried a cheapo usb wifi adapter based on the MT7601u. There is a linux driver, but again, I couldn't get it to compile on CentOS7.5. I'm probably doing something wrong, though. I don't understand toolchains and linux source and all of that stuff, though I do have gcc and the kernel source/headers installed.
I also tried a TP-Link TL-WN823N v3. Many of the reviews on amazon said it would work with various linux distros. No luck. lsusb sees a device, but no pre-installed drivers. I downloaded the drivers from jan 2018 for linux, and managed to compile and install them after following the instructions and editing the makefile. However, centos thought it was a usb-ethernet, not usb-wifi device. No matter what I tried to do with network scripts, I couldn't get it to come up as a wifi adapter, so I couldn't select the network and enter the password, so it didn't work. UGH
I caved and purchased a Think Penguin Wireless-N usb wifi adapter. They're about $27 on US eBay. It just works with CentOS 7. However, I had to use nmtui to delete the old wifi connections before plugging it in, or no wifi adapters would work. Probably some sort of conflict from trying to connect to the same wifi network with different hardware. The only downside is that it doesn't work with windows, so if I boot my windows drive, I have to switch USB adapters. Can't win 'em all I guess....