Billal Begueradj's questions

On Terminal, when I try to run Firefox, I get this message:

Command '/usr/bin/firefox' requires the firefox snap to be installed.
Please install it with:

snap install firefox

But it is already installed:

[sudo] password for begueradj: 
snap "firefox" is already installed, see 'snap help refresh'

More information:

begueradj@p50:~$ apt list --installed firefox -a
Listing... Done
firefox/mantic,now 1:1snap1-0ubuntu3 amd64 [installed]
firefox/mozilla 123.0.1~build1 amd64
firefox/mozilla 123.0~build3 amd64
firefox/mozilla 122.0.1~build1 amd64
firefox/mozilla 122.0~build2 amd64

Edit:

which firefox
/usr/local/bin/firefox

How to solve this ?

I have installed Emacs 25 using Ubuntu Software. It works. But now I want to remove it and install Emacs 26, instead.

In Ubuntu Software, Emacs is not listed among the installed items. Why ?

When I run nvm alias default 12.8.0 I get this:

default -> 12.8.0 (-> v12.8.0)

But when I run node -v, I get v11.9.0 instead

Why is this happening ?

I keep getting, since several days, "System program problem detected" error message:

I always clicked on Report problem button but nothing happens.

I also run update and upgrade everyday.

What causes this ? How to get rid of it ?

In Ubuntu Mate version 16.04.5 LTS (Xenial) , I want to create a shortcut like Shift + PrtScr to screenshot, but I am not able to find where to do it.

When I go to Preferences -> Keyboard and Mouse -> Keyboard I do not find a way to set it there.

For the moment I type on Terminal: bash -c "DISPLAY=:0 mate-screenshot -a" to take a screenshot of a specific area, or mate-screenshot for the whole screen, but that is not practical.

Anyway on how to do it?

I noticed whenever I want to delete a folder containing a lot of data using a command line (sudo rm -r folder_name), the Terminal hangs on for the operation to terminate. But at the same time, when I manually delete a folder of similar size, the deletion is performed instantly without waiting.

Any explanation as to why this difference happens

I noticed whenever I source a file, the color of user@hostname changes:

Why?

I installed Python3.6 as described here:

sudo add-apt-repository ppa:jonathonf/python-3.6
sudo apt-get update
sudo apt-get install python3.6

Then I installed numpy as follows:

sudo apt-get install python3-numpy

I guess I can import numpy from Python3.5 but not from Python3.6

Python 3.6.5 (default, Mar 29 2018, 03:28:50) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/numpy/__init__.py", line 180, in <module>
    from . import add_newdocs
  File "/usr/lib/python3/dist-packages/numpy/add_newdocs.py", line 13, in <module>
    from numpy.lib import add_newdoc
  File "/usr/lib/python3/dist-packages/numpy/lib/__init__.py", line 8, in <module>
    from .type_check import *
  File "/usr/lib/python3/dist-packages/numpy/lib/type_check.py", line 11, in <module>
    import numpy.core.numeric as _nx
  File "/usr/lib/python3/dist-packages/numpy/core/__init__.py", line 14, in <module>
    from . import multiarray
ImportError: cannot import name 'multiarray'

How to fix this issue?

I installed Ubuntu 18.04. Yesterday I had no trouble with WiFi connection. Today, I connect to the same hotspot but I am not able to connect:

Error resolving 'hotspot_name': Name or service not known

Here is how I set the content of the relevant files:

/etc/hostname

begueradj

/etc/hosts

17.0.0.1 localhost
17.0.1.1 begueradj

I did not have /etc/cloud/cloud.cfg but I created it and set: preserve_hostname: true

I run: sudo service network-manager restart

I am still getting the same problem

Any suggestions?

I installed OBS Studio:

sudo apt-get install obs-studio 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  gir1.2-keybinder-3.0 libkeybinder-3.0-0
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  libfdk-aac0 libluajit-5.1-2 libluajit-5.1-common libxcb-xinerama0
The following NEW packages will be installed:
  libfdk-aac0 libluajit-5.1-2 libluajit-5.1-common libxcb-xinerama0 obs-studio
0 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Need to get 3,678 kB of archives.
After this operation, 13.0 MB of additional disk space will be used.
Do you want to continue? [Y/n] 

I decided to remove it:

sudo apt-get --purge remove obs-studio Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  gir1.2-keybinder-3.0 libfdk-aac0 libkeybinder-3.0-0 libluajit-5.1-2
  libluajit-5.1-common libxcb-xinerama0
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
  obs-studio*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 11.6 MB disk space will be freed.
Do you want to continue? [Y/n] 

When removing it, I expect 13.0 MB of disk space to be freed because that is what the installation required, but I got 11.6 MB disk space freed instead: Why?

I used MPlayer to record the desktop and webcam on the same time.

mplayer tv:// -tv driver=v4l2:width=400:height=300 -vo xv -geometry 100%:100% -noborder

(credit)

How to save the result into a file?

I installed MikTex following this tutorial:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys D6BC243565B2087BC3F897C9277A7293F59E4889

echo "deb http://miktex.org/download/ubuntu xenial universe" | sudo tee /etc/apt/sources.list.d/miktex.list

sudo apt-get update

I got this note message:

N: Skipping acquire of configured file 'universe/binary-i386/Packages' as repository 'http://miktex.org/download/ubuntu xenial InRelease' doesn't support architecture 'i386'

How to get rid of this?

I installed guvcview, when I try to record a video, it records my voice and one single image. It does not record all the frames (images). How to solve this?

On one of my old computers, I have Lubuntu 16.04.4 LTS.

My OS can not find drivers for HP Envy 4526 printer.

What can I do? I am not able to print for the moment (thought the printer is recognized)

When I run: sudo apt-get install libpng12-0, I get this error message:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package libpng12-0 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libpng12-0' has no installation candidate

• How to fix this?
• Is having libpng16-16 installed enough to do what libpng12-0 does?

I have:

Distributor ID: Ubuntu
Description:    Ubuntu 17.04
Release:    17.04
Codename:   zesty

When I run apt-get update, I get this error message:

Err:18 http://dl.google.com/linux/chrome/deb stable Release.gpg                
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6494C6D6997C215E

I understand what causes this issue. I wonder how to fix it.

EDIT:

I tried the most upvoted solution provided in the duplicate link:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6494C6D6997C215E

I got this new issue which does not seem to be resolved on this website according to the posts I saw:

Executing: /tmp/tmp.jyolnTyZuJ/gpg.1.sh --keyserver
keyserver.ubuntu.com
--recv-keys
6494C6D6997C215E
gpg: requesting key 997C215E from hkp server keyserver.ubuntu.com
gpg: keyserver timed out
gpg: keyserver receive failed: keyserver error

To minimize all the open windows, I use Ctrl + Window + D.

Is there an icon like stuff that I could drag and drop to the taskbar as a click is quicker and easier for me than a 3 simultaneous buttons press?

I installed Tor this way:

sudo add-apt-repository ppa:webupd8team/tor-browser
sudo apt-get update
sudo apt-get install tor-browser

I run today in Terminal this: $ tor and I got this error message:

Oct 04 19:24:04.461 [notice] Tor v0.2.7.6 (git-605ae665009853bd) running on Linux with Libevent 2.0.21-stable, OpenSSL 1.0.2g and Zlib 1.2.8.
Oct 04 19:24:04.461 [notice] Tor can't help you if you use it wrong! Learn how to be safe at https://www.torproject.org/download/download#warning
Oct 04 19:24:04.517 [notice] Read configuration file "/etc/tor/torrc".
Oct 04 19:24:04.574 [notice] Opening Socks listener on 127.0.0.1:9050
Oct 04 19:24:04.574 [warn] Could not bind to 127.0.0.1:9050: Address already in use. Is Tor already running?
Oct 04 19:24:04.575 [warn] Failed to parse/validate config: Failed to bind one of the listener ports.
Oct 04 19:24:04.575 [err] Reading config failed--see warnings above.

How to fix this?

How to install OpenCV version 3.1 on Ubuntu 16.04 LTS to work with Python 3.5.1?

I tried this on a VM but obviously that is useful to do if you want to work with Python 2.

How to install the Python (3) wrapper for libdnet on Ubuntu 14.04.4 LTS? I need is as it is a pre-requisite to ScaPy, however the Python 3.x wrapper does not seem to exist yet.