martin_0004's questions

My OS: Ubuntu 18.04.5 LTS

I use tracing for troubleshooting a script. I've notice different behaviors in the tracing depending on how I set it up. I would like to understand why it behaves this way.

I normally activate tracing using set -x in my script where I need the tracing to take place. However the Prompt String PS4 ("+ " by default) seems to "duplicate" itself.

If I active tracing in the shebang #! line, PS4 is only printed once.

Similarly, if I call bash directly for running my script, and specifying -x in the command line, PS4 is also only printed once.

Why is set -x behaving differently in the first example ? I guess there is something fundamental about the shell which I am not getting here...

I installed Notepad++ in Ubuntu 18.04.5 LTS using Ubuntu Software. Notepad++ was installed under /snap.

I am trying to copy a new style file:

~/Desktop/Cobalt.xml

into the Notepad++ themes folder.

sudo cp Cobalt.xml /snap/notepad-plus-plus/238/winedata/Application\ Data/Notepad++/themes

I get the following error:

cp: cannot create regular file '/snap/notepad-plus-plus/238/winedata/Application Data/Notepad++/themes/Cobalt.xml': Read-only file system

I was able to copy the file in folders /snap and /snap/notepad-plus-plus, but somehow from folder /snap/notepad-plus-plus/238 it doesn't work anymore...

Any idea how to go around this ?

I am trying to use minicom to communicate with an ESP8266 Wifi chip using AT commands. I log into minicom and I type command "AT". The normal answer of the chip would be to send "OK" back to minicom. However, after typing "AT", once I type "Enter" the cursor goes back to the beginning of the line and nothing happens. It is as though the command had not been sent.

I log into minicom with

sudo chmod a+rwx /dev/ttyUSB0
sudo minicom -D /dev/ttyUSB0 -b 115200

In the Arduino IDE Serial Monitor, I am able to communicate with the chip by setting baud = 115200 and "Both NL & CR". When sending command "AT", the chip sends back answer "OK". I am trying to reproduce the same in minicom.

Any idea why the command doesn't get sent ?

Update

I saw in many minicom tutorials that command prompt cmd> should appear. Yet it does not appear on my screen. Maybe this is an indication that minicom is only in "listening" mode, and not in "waiting for command from the user" mode ?

I am using the bluetoothctl utility to set up Bluetooth connections between computers and Raspberry Pis.

In bluetoothctl, I can see there is something called an "agent", and by looking at most of tutorials, this "agent" has to be set "on" to create connections. I am trying to understand what is a bluetooth agent.

1) What is a bluetooth agent ?

2) What is the "default-agent" command in bluetoothctl for ? Can it be the same for all connections ?

3) What is the impact of not using an agent when setting up a connection ?

4) By looking at man bluetoothctl, it is said that agents can be set a capability. What is an agent capability ? What values could be put there ?

5) Do agents only exist with bluetooth ? Are there let's say wifi agents too ?

I am fairly new to the world of Bluetooth, and the documentation for bluetoothctl is quite limited... Any information would be appreciated.

Basic question regarding the ls utility. What do letters b and c mean at the beginning of the 10-symbol code describing the items' privileges?

From what I understand, when typing ls -l, the terminal provides a list of all items in a directory. Each item description is preceded by a 10-symbol code. This code says what the item type is (first symbol) and what the item privileges for the user, the user group and all other users are.

• If the first symbol is a dash -, the item is a file.

• If the first symbol is the letter d, the item is a directory.

• If the first symbol is letter l, the item is a link / shortcut.

For example:

$ ls -l /home/phodor
total 68
drwxr-xr-x 5 phodor phodor 4096 Dec 20 12:02 Documents
drwxr-xr-x 9 phodor phodor 4096 Jan 17 12:02 Desktop
drwxr-xr-x 7 phodor phodor 4096 Jan 13 22:42 Downloads
-rw-r--r-- 1 phodor phodor 8980 Jun 27  2015 hello.txt
lrwxrwxrwx 1 phodor phodor   29 Jan 17 12:02 MyEBook -> /home/phodor/Documents/EBook.pdf

However some the 10-symbol code can also start with b or c for some items:

$ ls -l /dev
crw--w---- 1 root tty  4, 0 Jan 17 09:19 tty0
brw-rw---- 1 root disk 1, 0 Jan 17 09:19 ram0
brw-rw---- 1 root disk 8, 0 Jan 17 09:19 sda

What do b and c mean? What is the full list of values that the first symbol of the file description code can take (-, d, l, b, c, ...)?

I have an Arduino Uno connected to an HC-05 Bluetooth sender/receiver chip. I am trying to create a Bluetooth connection between my Acer laptop running under Ubuntu 14.04 LTS and the HC-05 chip.

Ubuntu detects the HC-05 chip, as can be seen below.

phodor@ubuntu: hcitool scan
Scanning ...
    11:22:33:44:55:66   HC-05

I am able to create a pair between my laptop Bluetooth device and the HC-05 chip. However, I am unable to create a connection with that pair from the Ubuntu interface. The "Connection" button cannot be clicked on, as you can see on the figure below.

I tried creating a connection using the terminal, but after that the terminal still did not detect any connection.

phodor@ubuntu: sudo hcitool cc 11:22:33:44:55:66
[sudo] password for phodor: 
phodor@ubuntu: hcitool con
Connections:

I also checked that my computer Bluetooth device was working.

phodor@ubuntu: hcitool dev
Devices:
    hci0    AA:BB:CC:DD:EE:FF

Any idea why the connection cannot be created ? Any idea on how to do it using the Ubuntu interface or the terminal ?

Where does Ubuntu 14.04 LTS store LibreOffice icons ? I mean by that the icons used by the GUI of LibreOffice Writer, LibreOffice Calc, LibreOffice Impress...

I connected an AOC usb monitor to my Acer Aspire laptop which is using Ubuntu 14.04 LTS. I then installed the DisplayLink driver. Unfortunately, the AOC monitor remains dark. Any ideas how to troubleshoot this ?

Informations about my system

1) Monitor: AOC usb monitor e1649Fwu

2) Laptop: Acer Aspire E 15 - ES1-511-C723 - Intel Celeron Processor N2830

3) DisplayLink Driver: http://www.displaylink.com/downloads/ubuntu.php (available since August 3rd, 2015, quite recent when I posted this message).

4) Ubuntu & Linux Version:

uname -a
Linux MYCOMPUTER 3.16.0-45-generic #60~14.04.1-Ubuntu SMP Fri Jul 24 21:16:23 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Some more observations

1) The AOC usb monitor has 2 usb connectors. One is plugged in a laptop USB 3.0 socket and the other in a usb 2.0 socket.

2) When I plug in the AOC monitor or on computer boot, the AOC monitor flashes for a fraction of a second, then remains dark.

3) When I move the cursor to the right limit of my laptop main monitor, the cursor disappears and jumps into the usb monitor space (yet I cannot see it because the usb monitor is dark).

4) The AOC usb monitor is somehow detected by Ubunty (Device 011 below)

lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 004: ID 04f2:b47f Chicony Electronics Co., Ltd 
Bus 001 Device 007: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller
Bus 001 Device 006: ID 093a:2510 Pixart Imaging, Inc. Optical Mouse
Bus 001 Device 008: ID 04ca:300b Lite-On Technology Corp. 
Bus 001 Device 003: ID 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB
Bus 001 Device 011: ID 17e9:4107 DisplayLink 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

5) When the AOC screen is connected, the mouse on my main monitor flashes really fast and sometimes disappears.

6) When I do a print screen, Ubuntu captures images from two monitors (see images below).

7) In Systems Settings -> Screen Display, the AOC monitor shows as FNM 0" (images below contain the screen display data of both the main laptop monitor and AOC monitor).

Any ideas how to troubleshoot this ?

How can I modify the screen brightness in Ubuntu 14.04 LTS ? In the Systems Settings -> Brightness & Lock screen, all I see are options related to the screen saver, but nothing for changing the current screen brightness. Shouldn't there be a scroll bar for brightness level in this window ?

Most of bash commands have an help manual which can be opened in the command line by using the command man:

man bash
man ssh_config
man sshd

On the first line of every man page for a command, we can see the name of the command immediately followed by a number within parentheses:

bash(1)
ssh_config(5)
sshd(8)

What does this number mean ? Does any of you know a page which would list all possible values of numbers which can appear between these parentheses and their meaning ?

I would like to perform a VNC remote desktop session with Remmina between two computers running Ubuntu 14.04 LTS. I am able to do this remote session when a user is already logged into Unity on the remote computer. However, if the computer has just booted and the Unity log in screen is visible (i.e. that a user hasn't logged in yet), I am unable to start the remote desktop session. This forces me to physically go to the remote computer and log in so I can start the remote desktop session.

A solution would be to configure users on the remote computer to automatically log in into Ubuntu, but I would like to avoid this since it is not a secure configuration.

Any ideas on how Remmina could start a VNC remote session even if no users are logged in on the remote machine ?

I am trying to create a new user in Ubuntu 14.04 LTS from the bash command line. I use the following commands:

sudo useradd -c "Samwise the Brave" sam    
sudo passwd sam    
Enter new UNIX password: hello-1234    
Retype new UNIX password: hello-1234    
passwd: password updated successfully

After creating this new user, I encountered 3 issues:

1. I am not able to log into Ubuntu using user sam. Whenever I log in, I am sent back to the login screen.

2. When I look into the /etc/passwd file, I can see that there are no default shells defined for user sam:

   cat /etc/passwd | grep sam    
   sam:x:1003:1003:Samwise the Brave:/home/sam:
   

3. Sam's home folder was not created, i.e. /home/sam doesn't exist.

Any clues about what could cause all these issues?

I should note here that when I create a user using the Unity Control Center, these problems do not occur. But I would like to be able to use the command line since I have dozens of users to create.