Separation Anxiety: A Tutorial for Isolating Your System with Linux Namespaces

With the advent of tools like Docker, Linux Containers, and others, it has become super easy to isolate Linux processes into their own little system environments. This makes it possible to run a whole range of applications on a single real Linux machine and ensure no two of them can interfere with each other, without having to resort to using virtual machines. These tools have been a huge boon to PaaS providers. But what exactly happens under the hood?

journalctl command to see kernel messages

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

ionice – renice you IO activity for the process.

ionice is utility provided by the package util-linux. Description of util-linux:

Description : The util-linux package contains a large variety of low-level system

utilities that are necessary for a Linux system to function. Among

others, Util-linux contains the fdisk configuration tool and the login

program.

 

With the help of this utility, you can set the scheduler priority for your IO scheduling upto RealTime, but be careful that can make other process sluggish. Example use:

zswap – compcache, compressed swap for better performance

First, here is a link to article on compcache.

http://code.google.com/p/compcache/wiki/CompilingAndUsingNew

zswap is already in the kernel and you can see the documentation in the kernel documentation. Here is the name of the file if you need:

/usr/share/doc/kernel-doc-$(uname -r)/Documentation/vm/zswap.txt

Here is the overview, in case you do not want to install kernel-doc

Overview:

Zswap is a lightweight compressed cache for swap pages. It takes pages that are
in the process of being swapped out and attempts to compress them into a
dynamically allocated RAM-based memory pool.  zswap basically trades CPU cycles
for potentially reduced swap I/O.  This trade-off can also result in a
significant performance improvement if reads from the compressed cache are
faster than reads from a swap device.

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Kernel ata exception — found workaround.

I have been getting the below errors in my system for quite sometime now, I think since F9 or before that. The offending hardware is CD drive. I looked all around the net for a solution but did not find anything. Will keep looking to solve the problem. I found various solutions being suggested like adding noirq or nobiosirq or noacpi and such. None of this helped. So for now I am happy with turning off the haldaemon as soon as the system comes up. Problem: it takes lot of time to go down 🙁

Are you swapped? Increase the performance of Linux machine.

With the ever increasing cost of the Hardware, the amount of physical RAM available on the system is increasing day by day. For example, couple of years back, I had a system which was very high end Desktop with 256MB RAM and today I have a 2GB RAM Desktop. So, whats the point.

The Linux systems (right word should be kernel) are desiged to use both RAM and swap partition. Swap partition is a partition on Hard disk and is used mostly like RAM. Problem is that HDD access is always slower than RAM access and hence inherently, the system will work little slower even if you have enough RAM not to use swap. The term ”swappiness” is used to determine how the kernel should try to seam-balance between the use of RAM and swap. By default, most of the distro’s have a swappiness of 60. A higher value of swappiness means that the RAM will be swapped out faster.

Getting the list of IOCTLS in the kernel.

Sometime back I was helping one of my friends in looking for all the IOCTLs supported by the kernel. Well we did not find the info we were looking for and thus thought to write a perl script to get all the IOCTLS supported by the kernel. Here it is, simple script to scan through the code and give you a list:

#!/usr/bin/perl —

@files = `grep -r ” _IO” /usr/src/redhat/SOURCES/linux-2.6.20/* |grep define ioctls_grep`;
open (DAT, ”ioctls_grep”) ||die ”could not open ioctls_grep”;
@files = DAT;
close(DAT);
my %ioctls_numbers;
print ”Grep completed..\n”;
open (DAT, ”ioctls_numbers_found”);

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