Category: Linux

Categories
Linux Red Hat Ubuntu

Bash: remove trailing slash from a variable

Suppose you have a variable containing a directorypath:

#!/bin/bash
directorytouse="/home/myhome/whateverdirectory/"

If you try to test in your bash script if the directory exists, then it will fail because of the trailing slash:

if [ ! -d "${directorytouse} ] 
then
    echo -e "directory does not exist!"
fi

The easiest way to remove this / if it is present is to use shell parameter expansion:

if [ ! -d "${directorytouse%/}" ]
then
    echo -e "directory does not exist!"
fi

This will get rid of the trailing slash if there is one. If there is no trailing slash present, then nothing will happen.

Categories
Linux Red Hat Ubuntu

Help, my terminal shows graphical characters instead of normal text

If you have ever used cat or tail to accidentally show a binary file, you will have noticed your terminal show graphical garbage instead of readable text. As shown in the screenshot below:

You will find several suggested fixes on the internet for this, including:

  • type CTRL-C a few times to make sure you are on a new line and then enter ‘reset‘ and tap enter.
  • output the ASCII SI (shift in) character, decimal value 15. This can be entered with CTRL+O and should work if the reset command doesn’t work. Just enter ‘echo CTRL+V CTRL+O’ on the command line
  • enter the command ‘stty sane’, followed by ‘tput rs1’ on the command line.

The only one that worked for me is entering the following (blindly, since you can ‘t read what your are typing) on the terminal prompt:

echo -e "\033c"

A good practice is to define an alias in your startup script with the following command:

alias resetterminal='echo -e "\033c"'

Next time you have this problem, you can then type (blindly) ‘resetterminal’ to fix the problem.

Categories
Linux Red Hat Ubuntu

Vi (or Vim) session no longer responding?

If your Vi or Vim session is hanging and is not responding to anything, then it might be because you pressed CTRL+S accidentally (out of habbit). To fix this, just press CTRL+Q to unblock the session.

Categories
Dell XPS15 Laptop Linux Ubuntu

No wifi or no external monitor on Dell XPS-15

If your wifi card is not available after booting your Dell XPS-15 laptop (with Ubuntu 20.04 or 22.04), or your external monitor refuses to display anything, please try the following:

start up your laptop without your power supply plugged in, connect with wifi, and/or your external monitor and only then plug in your power supply.

This fix works everytime for me.

Categories
Linux

Ubuntu: reset monitor settings to default

If you want to reset your monitor settings to default through the terminal (your second screen is broken and the settings are ‘shown’ there and you don’t want to restart your laptop), you can use the following command:

xrandr -s 0
Categories
Linux Ubuntu

Ubuntu Server – CTRL-ALT-DEL

If you press CTRL-ALT-DEL on a Ubuntu Server the server will be shut down without asking any confirmation or password. This is of course not a good idea.

To disable this, enter the following commands as root:

systemctl mask ctrl-alt-del.target
systemctl daemon-reload
Categories
Linux

Linux: removing commands from history

If you want to remove some commands from your bash history use the following command:

history -d 1001

where 1001 is the number of the history line. Of course this might add another problem: the command ‘history -d 1001’ is now added to your history.

How to avoid a command getting in your bash history?

If you want to execute a command and don’t want it to get in your history list (because it contains sensitive data, or you just don’t want to clutter your history), start the command with a space.

For this to work the environment variable $HISTCONTROL has to be set to ‘ignorespace’ or ‘ignoreboth’.

export HISTCONTROL=ignorespace
Categories
Linux

Ubuntu 20.04: annoying popup ‘Authentication is required to run gvfsd-admin daemon’

If you get the above popup, and it is impossible to get it to go away (cancel does nothing, authenticate hangs…), here is a quick solution to get rid of it:

Press ALT+F2, enter ‘r’ (without the quotes) in the command box and press enter. This will restart Gnome and the window will be gone. Your running apps keep running!

Categories
Linux

Ubuntu: external screen goes black, but ubuntu is still using 2 screens

Today I had the problem that my external screen was only showing a nice shade of black. However, several programs were running on that screen, and I could not just reboot the laptop without losing much work.

To fix this (it did fix it for me, your mileage may vary), open a terminal window (Ctrl + Alt + t) and type the following command:

xrandr

After this, I had my second screen back.

Categories
Linux Zentyal

Zentyal: how to change password expiry options

Zentyal is a great replacement for Windows domains, but in the webinterface there is currently (version 6) no option to change the password expiry settings.

To change them anyway, open a linux terminal on the Zentyal server and use the samba-tool utility


samba-tool domain passwordsettings set --max-pwd-age=0

This will turn off password aging. Change the 0 to the number of days you want to set it to expire to anything else than the default 365 days. Have look at the help page or manpage for samba-tool to see more options. If the command executes successfully, you will see the following text:

Maximum password age changed!
All changes applied successfully!

and you are done!