Debugging on Amit Agarwal Linux Blog

journalctl command to see kernel messages

Mon, 30 Jan 2017 01:19:12 +0000

Sometimes, there are just too many messages in journalctl output and it becomes a mystery game to search for the messages you are looking for. But luckily you do not need to use grep to find the right message. Here is example of what I had to do when I was looking for kernel messages.

journalctl _TRANSPORT=kernel
# To see all the fields, you can use the verbose mode
journalctl _TRANSPORT=kernel -o verbose

# And the filter on priority if needed to get the messages you need
journalctl _TRANSPORT=kernel PRIORITY=4

# and follow
journalctl _TRANSPORT=kernel PRIORITY=4 -f -l

speed up journalctl

Mon, 25 Apr 2016 00:40:56 +0000

Sometime back I noticed that whenever I run my favourite command, viz.

journalctl -xn -f -l

it was taking more time than usual. So, I thought to dig more into it and finally found that the following command:

sudo journalctl --disk-usage

showed that journalctl was using some huge space in tune of about 4GB. So, the solution was simple, vaccum the journal entries and the command to do so is :

sudo journalctl --vacuum-size 90M

Checking journalctl size after that confirms the size is reduced and after that indeed the above journal command takes no time 🙂

better bash debugging

Fri, 16 Sep 2011 08:00:08 +0000

I was trying to debug some bash scripts yesterday and learnt something new 😉
There are lot of things in bash that you can use to debug and to start with you can enable xtrace mode as follows:

set -x

With this set you will see that all the commands are printed along with all other information as they are executed.
This you can do for any line or for the function or for the whole script. Once you set the option you can turn it
off with

debug call function() to debug a function in vim

Sun, 04 Sep 2011 06:04:53 +0000

Image via Wikipedia

Have you ever wished that you could either see what is going on initially at the vim startup like you could do with C program in the gdm mode, but really did not want to go through gdb. Or rather you sometime felt that some function defined by some plugin is causing some issue and you wanted to debug just that function. Well you need not wish anymore, the functionality is already there.

/bash debugger

Sun, 27 Feb 2011 13:09:48 +0000

9.2. A bash Debugger

In this section we’ll develop a very basic debugger for bash.[10] Most debuggers have numerous sophisticated features that help a programmer in dissecting a program, but just about all of them include the ability to step through a running program, stop it at selected places, and examine the values of variables. These simple features are what we will concentrate on providing in our debugger. Specifically, we’ll provide the ability to: