LINUX BUILT-IN SCREENSHOT & SCREEN RECORDER COMMAND

Screenshot shortcuts:
PrtSc (Save a screenshot of the entire screen to the “Pictures” directory)
Shift + PrtSc (Save a screenshot of a specific region to Pictures)
Alt + PrtSc (Save a screenshot of the current window to Pictures)
Ctrl + PrtSc (Copy the screenshot of the entire screen to the clipboard)
Shift + Ctrl + PrtSc (Copy the screenshot of a specific region to the clipboard)
Ctrl + Alt + PrtSc (Copy the screenshot of the current window to the clipboard)

Screen recorder shortcut:
Ctrl + Alt + Shift + R (Start or stop recording)

Screen recorder command:
$ gsettings set org.gnome.settings-daemon.plugins.media-keys max-screencast-length 60

(Sets the recording time to 60 seconds, default value is 30 seconds)

[SOLVED] CENTOS 7.X / RHEL 7.X WIFI NOT CONNECTED

In my case, WiFi was detected but the signal was too weak. When I tried to connect, error message 'Could not activate connection: Activation failed' appeared.

Finally, I figured out the root cause - it was Realtek RTL8723BE driver. 

These steps below solved the issue in both CentOS 7.x and RHEL 7.x:

1. Download Realtek RTL8723BE PCI-E Wireless driver here

2. Extract the file

3. Right click on folder 'rtlwifi_new-rock.new_btcoex'
4. Click 'Open in Terminal'

5. Type these commands:

• make
• sudo make install
• echo "options rtl8723be ant_sel=1" | sudo tee -a /etc/modprobe.d/rtl8723be.conf or echo "options rtl8723be ant_sel=2" | sudo tee -a /etc/modprobe.d/rtl8723be.conf

6. Restart

Notes: The ant_sel parameter enables one of the two antenna connectors of your RTL8723be adapter. Your laptop has only one antenna because the vendor is too greedy to install two. The Linux drivers can't detect which antenna connector is in use. So we have to guess it.
In Windows either the vendor sets it up somewhere on a pre-installed system, or the Windows proprietary drivers can detect it.

If ant_sel=1 does not help, use ant_sel=2. This setting tells which antenna is in use 1 or 2.