39 cards

Debugging microphone issues in Linux and Zoom


Since Zoom does some post-processing of your audio input, it's best to hear yourself in a Zoom recording:

  • Open a Zoom meeting for yourself.
  • Choose "Record to this computer" in the Zoom toolbar.
  • Speak some words (quiet and loud) and allow some seconds of silence.
  • End the meeting.
  • Zoom will open a folder with an audio recording.
  • Listen to the audio recording.

Check microphone settings in Linux

Right-Click on the speaker icon in your tray, then go to Sound Preferences => Input.

Selecting the correct microphone...

Zoom: Fix gray shadow during screen sharing

When sharing a screen over Zoom in Ubuntu MATE Archive , you might notice a dark gray shade.

This shade is caused by the Compton compositing manager, which you probably enabled in MATE Tweak / Windows / Window manager. Zoom draws a green rectangle around your screen to indicate what is being shared, and Compton draws a "shadow" into this rectangle.

Emergency fix

If this happens to you during a meeting, you can quickly "fix" it by stopping Compton from the console:

killall compton

The shado...

What to do when your GPG/PGP key expires

Your GPG client notified you that your keypair will soon expire, or has already expired. Here is what to do.

Are you using Thunderbird?

If you're using the built-in GPG encryption in Thunderbird 78+, you can extend your key from the Thunderbird key manager.

Suggested way: Extend your key expiry Archive

  1. Find the ID of the expiring key, e.g. with ...

GPG: Extract private key and import on different machine

After extending the expiry date of a GPG key you might have to copy your key to another machine to use the same key there. Here is how:

  1. Identify your private key:

    gpg --list-secret-keys user@example.com

    Example output:

    pub   4096R/ABC12345 2020-01-01 [expires: 2025-12-31]
    uid                  Your Name <user@example.com>
    sub   4096R/DEF67890 2020-01-01 [expires: 2025-12-31]

    Remember the ID of your key (second column, after the slash, e.g. "ABC12345"). If you have a "sub" entry, you can ignore it.


Thinkpad Fix: Touchpad scrolling is not working after suspend

I noticed that after suspending my notebook, the thouchpad scrolling (at the edge or with two fingers) was not working any more. This seems to be a known bug Archive

My setup is:

  • ThinkPad T480
  • Ubuntu MATE 18.04

The linked comment above solved the problem for me:

You have to edit the file /etc/default/grub (sudo!) and change this line:

# from:


# to:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash psmouse.synaptics_interto...

When attachments and calendar invites appear as winmail.dat

When an incoming e-mail contains a single attachment named winmail.dat, a Windows user has misconfigured their Outlook client. They are probably trying to send you an attachment or calendar invite, which are now compressed into the winmail.dat attachment using a proprietary format. Outlook will also attach a winmail.dat if such an user wrote a formatted e-mail.

Ask the sender to fix their Outlook

If possible, ask the sender to fix their Outlook configuration:

  • [English instructions for Outlook u...

How to set a fixed microphone source in Ubuntu if it keeps changing

In some circumstances it's possible for Ubuntu to switch the default microphone on its own, e.g. if you're using a headset connected by a 3,5mm plug and your USB webcam also has a microphone, Ubuntu might set the default microphone to the USB one in the webcam.

If that's not what you want, it's suprisingly hard to tell Ubuntu not to do it. Here is how.

Alternatively, you may disable all devices but the one you want to use. Note that this is not always applicable, e.g. if you want to keep your ot...

How to avoid 100% CPU load when screen-sharing through zoom

Zoom Archive is a video conference tool that has great screen-sharing support on Linux. [1]
However, Zoom's screen sharing causes immense CPU load, slowing down other applications, and on laptops the CPU fan going at full speed will drive you insane.

To fix that, open Zoom's settings dialog (cog icon in the top right), and in the "General" section set the "Limit your screen share to X frames per second" option.
I suggest you set to 4 FPS. This may sound very low but is actually enough for pair programming or demoing something.


Useful Zoom shortcuts

| alt + q | End Meeting ("quit") |
| alt + a | Toggle Mute ("audio") |
| alt + s | Share Screen ("share") |
| alt + i | Open invite menu ("invite") |

For more shortcuts see the zoom help Archive .

Snom VOIP phone shows your own name instead of the incoming number

This is because of how Sipgate sends the incoming caller ID. As it is intended, it shows both who the call is for (in case you have multiple numbers configured on your phone) and who it's from, after a line break. Neither SNOM phones nor linphone, ekiga, etc handle this perfectly. You may either fix this only on your SNOM phone or on all connected clients:

SNOM phone fix only

  • Log into the web interface of your phone (yes, your phone has a web server) by opening its IP address in a browser. You can find the IP address in the phone'...

Ensure screen lock on suspend

Ubuntu Mate 18.04 has a bug in which suspending your computer does not lock your screen in every case. If closing your laptop's lid or clicking the suspend menu option in your top right menu already locks the screen, you're not affected and don't need to do anything.

Step 1

To make sure screen lock is engaged when you suspend your computer, please create the following file, as root:


Description="Make extra sure to lock the screen when suspending"


Presenting on Linux: Screen mirroring with incompatible projector resolutions

When presenting with a projector, you probably want to mirror your screen. This way your laptop and the projector show the same image.

Your Linux display dialog will usually have a checkbox to mirror screens. However, checking this box might dramatically reduce the number of available resolutions. This is caused by incompatible lists of available resolutions between the both screens. Often you will end up with a very low common resolution, like 800x600.

What helps in such a case is to add the missing projector resolution for your laptop sc...

HowTo install Ubuntu's HWE stack for more recent kernel and grahpics drivers

With the latest hardware on both Laptops and Desktop computers, it might be necessary to install more recent hardware drivers, i.e. Linux kernels and xorg versions.

While it's possible to use backports from various sources on the internet, it's neither very safe nor tested very well. However, there is official support for the Hardware Enablement Stack in Ubuntu LTS-Versions, i.e. 16.04 and 18.04.

If your system is working fine without the HWE packages installed, it's best to just leave it alone. If you're sure issues on your s...

What to do when your Dell U2410 monitor fails to power on

Dell U2410 screens have a stupid firmware bug where when you manually switch off the monitor and then your computer, the screen will no longer power on when the computer is restarted. In such a case the power button is dead and no longer reacts to input.

In order to fix this:

  • Remove the power cable from the monitor
  • Wait for 10 minutes
  • Replug the power cable


Take care with dates in English e-mails

The English speaking world does not agree on how to write dates. For the 21st of June, Americans use "06/21/2018", while the British use "21/06/2018".

To avoid confusion, prefer to write either "June 21, 2018" (which is American English), or "21 June 2018" (which is British), but which cannot be misinterpreted.


Configure CSipSimple for Sipgate

The default settings used by the wizard did not work for me. I got authentication errors all the time.

This is what worked for me:

Account name: Sipgate.de
SIP-IP:       Your Sipgate ID (see https://secure.live.sipgate.de/settings/phone/, click on phone and select "Show SIP credentials")
SIP-Passwod:  You Sipgate password (see link above)
SIP Server:   sipgate.de:5060
Proxy:        proxy.live.sipgate.de

If you have trouble with CSipSimple, try [Zoiper](https://makandracards.com/makandra-orga/4...

Linked contentDeprecated

Using GPG/PGP with Ubuntu and Thunderbird

When transmitting sensitive information, we never want to send unencrypted e-mails, but use GPG/PGP encryption.

Creating a key pair

  • Before starting, create a new entry in KeePass for your GPG key and create a new password. See the Security Guidelines for password policies.

  • Start generating a key by running the following command in your terminal

    gpg --full-gen-key
    • Select the default key type (RSA/RSA)
    • Choose at least 4096 bits for key...

How to change your dm-crypt passphrase

dm-crypt has multiple passphrase slots. The process will be to add a new passphrase to a new slot, check that it works, and then remove the old passphrase.

  1. Find out which partitions are decrypted by dm-crypt:
$ lsblk --fs
NAME                  FSTYPE      LABEL   UUID                                   FSAVAIL FSUSE% MOUNTPOINT
├─nvme0n1p1           vfat                65CB-0937                               503,2M     2% /boot/ef...
This website uses short-lived cookies to improve usability.
Accept or learn more