Reffffference

Ubuntu 20.04 Command ‘python’ not found

Sun, 30 Aug 2020 21:22:48 +0000

Canonical decided to move to python 3 for Ubuntu 20.04, which is great, you can start it with the command python3.

However there is programs that look for /usr/bin/python and this is not a binary found on the server.

So how do you solve this little problem? The idea behind that is that you might need either python 2 or python 3 for your programs so you can install either of them to be the default one, with two respective packages called:

i3wm brightness control on T480s

Mon, 19 Aug 2019 16:54:52 +0000

I got a new laptop – Thinkpad t480s – it is a great machine!
But since I like to use i3wm for my work, there was a bit of a problem with the way I control the brightness on my old machine. I had two scripts which were triggering when I press the function keys which were detected as XF86MonBrightnessDown and XF86MonBrightnessUp

The problem is that this newer machine was not detecting these keys with xev and when I was using the function keys for the screen brightness acpi events were triggered, so I needed to find how to catch the key presses.

Pipe mysqldump to ssh/sftp

Mon, 08 Jul 2019 15:24:42 +0000

If you need to send mysqldump over ssh on different server without creating any files on the local server, mostly if you are low on space you can use this:

mysqldump -u MYSQL_USERNAME -p DATABASE | gzip -c | ssh USER@HOST 'cat > ~/dump.sql.gz'

And for the restore from remote location:

ssh USER@HOST "cat /path/to/db.sql" | mysql -uUSER  -pPASSWORD DATABASE

Enabling query cache for MariaDB/MySQL

Thu, 27 Jun 2019 00:47:10 +0000

Query cache can speed up to 2-3 times queries that are often run.
It is pretty easy to set up. First you need to check if query cache is supported for your system:

show variables like 'have_query_cache';

That should return:

+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| have_query_cache | YES   |
+------------------+-------+

Then you need to check some variables related to query caching. I will explain each of them:

mysql> show variables like 'query_cache_%' ;
+------------------------------+----------+
| Variable_name                | Value    |
+------------------------------+----------+
| query_cache_limit            | 262144   |
| query_cache_min_res_unit     | 4096     |
| query_cache_size             | 10485760 |
| query_cache_type             | ON       |
| query_cache_wlock_invalidate | OFF      |
+------------------------------+----------+

query_cache_limit – the total size each individual query can be. In my case that is 262144
query_cache_min_res_unit – how large is each chunk/block of cached data
query_cache_size – the total amount of cached queries, 0 disables it, and it needs to be at least 40kb at the lowest to work. Usually the default is 16,777,216
query_cache_type – if the value is ON it means cache query is enabled. If it is OFF it means it is disabled.

CentOS Configure account to never expire / fix cron problem

Fri, 15 Feb 2019 15:47:08 +0000

CentOS have security measure to force users password expiration which can cause problems.
For example – you do not use passwords to log in to machines, and you prefer ssh keys. And the day the password for that user expires its cron jobs will stop working.

You can fix it with one of these, I prefer removing the expiration with chage:

chage -M -1 root

passwd -x -1 root

You can confirm with:

MariaDB master-slave cluster on Ubuntu

Fri, 08 Feb 2019 19:01:48 +0000

This article explains how to run MariaDB SQL server in as master/slave replication cluster on two Ubuntu virtual machines.

master: 192.168.122.25
slave: 192.168.122.26

1. Before anything else you need to update all packages on the two machines:

sudo apt update
sudo apt upgrade

2. First thing is to add the official MariaDB repo for the stable release from here – https://downloads.mariadb.org/mariadb/repositories/
In my case, for Ubuntu 18.04 I had to use this:

Top linux commands to use.

Mon, 24 Dec 2018 08:27:44 +0000

Table with the command I most often use and think are essential. Or some that are cool, but easy to forget/not so often used.


ctrl+r	Search in bash history
ctrl+e	Go to the end of the line
ctrl+u	Cut the characters before the cursor
ctrl+y	Yank/paste, it can paste what you cut with ctrl+u
ctrl+shift+c	Copy the marked text
ctrl+shift+v	Paste the text from the previous command
ctrl+d	Close bash sessions, same as to type exit
!$	Get the last argument from the previous command
!*	Get all the arguments from the previous command
history	Don’t add command to bash history. There is space in front of the command
disown -a && exit	Exit terminal, detach all background process, so they can run. Useful for long tasks.
fc	Open last command in editor. Fix very long one-liners if you mess them up.
ctrl+x+e	Compose command in the default editor and execute it on save.
curl ifconfig.me	Get your public IP from CLI.
very_long_command # label	Label long commands, so it it easier to find in history. Everything after # is not executed as it is bash comment.
rm !(.foo\|.bar\|*.html)	Remove all files except the ones with these extensions.
vim -x <FILENAME>	Encrypt file in vim.
man hier	Show filesystem hierarchy.
cat /etc/issue	Get distro name.
ps aux \| grep [p]rocess-name	Find the process you are looking for, without showing the grep command itself.

Remap print key to Super(windows) in i3wm

Tue, 16 Oct 2018 22:52:03 +0000

My laptop keyboard is little annoying – it have a Print Screen(PrtSc) button between my right control and alt keys – usually around that area you will find the windows(super) key, so I wanted to remap it, when i am using i3wm.

So first of all you need to make sure what is your key “called”, you can to that with the xev program.

Then you need to get your modifier map with: xmodmap -pm
In my case my output was this:

Mount directory into the RAM

Thu, 05 Jul 2018 20:20:44 +0000

Needed to mount WordPress cache folder into the RAM of one VPS, to get that little bit of extra speed.
To mount it temporary and see how it works for you, you can use:

mount -t tmpfs -o size=64M tmpfs /absolute/path/to/your/folder/

To make it permanent you need to add this in the /etc/fstab file:

tmpfs /absolute/path/to/your/folder tmpfs defaults,size=64M 0 0

Systemd simple service

Sat, 09 Jun 2018 22:46:13 +0000

This a template for simple sysmtemd service to change the ownership of a file, since in my case the file is in /sys and it is generated on boot, so using acl didn’t help me. I had to use this hack to change the ownership of a file on each boot.
What I need is a write permissions to a file in order to change the brightness on my laptop with i3wm.