Hi: I have just installed Slackware 14.2 and, during the installation chose NetworkManager (NM). At home I use a wi-fi modem to connect to the Internet. When running Xfce I find the NM icon with a red cross below and the message 'No network connection'. Well, then I click the icon and see my network has been detected. I select it and the system prompts me to enter a password. I begin to write the password but then and before I press the 'Connect' button a message appears saying This is very odd because the network was already disconnected. When finally I press the 'Connect' button what happens? Absolutely nothing. There is no notification saying what the result of the operation was. And the red cross is still there. I find this disconcerting. What can possibly be happening?

One other thing: in the same machine I have Ubuntu running. And it has absolutely no problem with the wi-fi.

Try switching the dhcp client in /etc/NetworkManager/conf.d/00-dhcp-client.conf. Uncomment dhclient and comment out dhcpcd.

Thanks. At certain point the installer gives four options one of which is 'NetworkManager'. There is a program one can run which gives the same four options, maybe netconfig, but I do not remember the name. Do you? It configures the network.

I forgot to mention: just after installation I had no problem connecting to the Internet. But several months later during which I did not use the machine, I found the situation described in post #1. Of course I did some use of the machine during those months.

I did exactly as you suggested but still same behavior as described in post #1.

You might have to disable IPv6.

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No, I'll do a fresh installation. In that way the initial conditions will be known to everybody. I think it won't fail again. I'll let you know soon.

Well, I have just reinstalled 14.2 and, unfortunately, still the red cross by the NetworkManager icon (No network connection). But now anyone who has installed 14.2 and hasn't touched anything will be in the same conditions as I am.

Did you auto start it on boot up?

What do you mean?

nano /etc/NetworkManager/conf.d/00-dhcp-client.conf

chmod +x /etc/rc.d/rc.networkmanager
/etc/rc.d/rc.networkmanager start

I got 'NetworkManager is already running (will not start it twice)'.

Just an anecdote but I had problems on one of my new systems with random disconnects which was at first really odd since I currently have at least 3 nearly identical installs of Current, all using the identical 5.11.11 kernel. After a lengthy search and a lot of back and forth to see what was different (since the others did not exhibit drops) I saw that I had blacklisted "kernel-firmware" in addition to the necessary for me other kernel entries but just on that one instance/install.

TLDR it may be valuable to insure you get kernel-firmware or even identify your wifi chipset firmware for "iwlwifi" and see if the chipset manufacturer publishes newer firmware to add to "/lib/firmware/<manufacturer>". My Intel AX201 no longer drops, even at highest speeds, after a firmware update. Hope this helps you.

I don't know if you read post #1 but there it says I have Ubuntu running on the same machine with no problems at all with the wi-fi. What can Ubuntu (18.04) do that 14.2 doesn't do?

Examining logs, dmesg, kernel log, messages. It may be you have more than one service fighting over WiFi interface. For instance you may have both wpa_supplicant and NM started. Also dhcpcd can manage interfaces the same way as NM does. If you want to use NM make sure wpa_supplicant and dhcpcd are not started on their own, NM will start them.