Category: Linux

How to create an extra swap space using file system

Sometimes you feel constrained due to the the RAM limit of your system especially when you are running heavy duty software’s, in this blog I’ll talk about how you can overcome this problem by hav‌ing an extra swap space to give you extra computing power

First of all you can execute swapon command to check how much swap space you already have in your system
$ swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    44732    -1

The above output gives you an indication that you already have a swap space at partition /dev/sda5. The numbers under “Size” and “Used” are in kilobytes. Though I have considerable amount of swap space configured on my system :), let’s continue and try to create a new swap using file system. Before starting with creation of swap space let’s make sure that I’ve enough disk space available in my system

$df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3       448G  123G  303G  29% /
udev            1.9G  4.0K  1.9G   1% /dev
tmpfs           767M   40M  727M   6% /run
none            5.0M     0  5.0M   0% /run/lock
none            1.9G  804K  1.9G   1% /run/shm

So I’ve a powerful system with 303G of disk space still available, that means I have a liberty of creating a swap space of my liking. I’ll user the data dump(dd) command to my supplementary swap file, make sure that you would be running this command using root user.
$dd if=/dev/zero of=/home/sandy/extraswap bs=1M count=512
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 2.41354 s, 222 MB/s

Now we have created a file /home/sandy/extraswap of size 512M which we will be using as a swap partition. Swap can be created by issuing mkswap command
$mkswap /home/sandy/extraswap
Setting up swapspace version 1, size = 524284 KiB
no label, UUID=685ac04a-ad31-48a8-83df-9ffa3dbc6982

Finally we have to run swapon command on our newly created swap partition to bring it into the game
$swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    46248    -1
$swapon /home/sandy/extraswap
$swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    46248    -1
/home/sandy/extraswap                   file        524284    0    -2

As you can notice when we first executed the swapon -s command at that time swap partition was not in the picture, once we executed the command swapon /home/sandy/extraswap  the swap partition was available.

One last thing that we have to do is to add the entry of this swap partition in our /etc/fstab file as with the next system boot the swap partition will not be active by default we have to do the entry of this swap in our /etc/fstab file.

Linux Utility to manage login to systems

One of the problem I used to have as build & release engineer is to manage login to huge number of boxes through my Linux system. At the scale of 5-10 machine it’s a not a big problem but once you have close to 100+ boxes then it is not humanly possible to remember the ip’s of those boxes.
The usual approach for this problem is to maintain a reference file, from where you map machine name with the ip & find the ip of the box from this file, but again after some time this solution seems to be not that efficient. Another solution is to have a DNS server where you can store such mappings & then you can access these machines using their names only, this is the idle solution but what if you don’t have DNS server also still you have to execute the ssh command ‘ssh user@machine”.

I developed a simple solution for this problem, I created a utility script connect.sh, this script takes machine name as an argument & then we have multiple conditions statements which checks which ssh command to be executed for the machine name.

#!/bin/bash
if [ “mc1” == $1 ]; then
    ssh user@
elif [ “mc2” == $1 ]; then
    ssh user@
elif [ “mc3” == $1 ]; then
    ssh user@
.
.
.
fi

This solution worked really well for me as now I’m saved from executing whole ssh command, also for machine name I’ve followed a convention i.e _ for example the entry for a machine for release environment that is hosting an application catalog the machine name would be release_catalog, similarly dev_catalog, staging_catalog, pt_catalog.. so you don’t have to remember machine names as well :).

Ubuntu Rest Assurer

Before I’ll start talking about this utility I would like to talk about the story behind the creation of this utility. Few days back we have a session ERGONOMICS about healthy lifestyle, one of the main thing was that a person should take a break after every 20 minutes. After the session I was having a chit chat about one of my colleague Rahul Narang & we were discussing about this 20:20:20 rule & then we thought about creating a utility that will force a person to leave his/her system after some stipulated time & that’s how the idea came about this utility.

So what this utility does
1.) It runs after every half hour or configured amount of time
2.) Prompts a snoozer dialog box which will allow a person to snooze the screen locking for some amount of time
3.) After that a lunching video will run for 10 seconds
4.) Once a lunching video completes the screen gets locked for a configured amount of time
5.) If user try to unlock the system before configured amount of time the utility will lock the screen again

This complete utility is created using shell script only, we have used couple of command to do that
vlc : To run a launcher video
zenity : To prompt a snooze dialogue box
gnome-screensaver-command : To operate on screen lock

You can find the source code of this utility at my github account
https://github.com/sandy724/REAS