speed up journalctl

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 🙂

Most simple and fast lightweight container with Fedora systemd

If you need to have a quick bash shell in sandbox with not network as well, then the most simple command I could find so far is:

sudo virt-sandbox -c lxc:/// /bin/bash

For this you will need to have libvirt-sandbox installed which you can do with the following command:

sudo yum install libvirt-sandbox

ssh – remove offending key.

Whenever a system/server is re-installed or the host key changed for any reason, you would have seen the “host key verification failed”. And as usual you would have to go to known_hosts file and delete the offending key. I will show you 2 simple ways to do this here.

The output that you get in such scenario is:

Offending ECDSA key in ~/.ssh/known_hosts:4

First, you can use sed to directly delete the offending key with a command like this :

DNS – simple and effective guide with history

Here is link to a very nice and definitive guide to DNS. Very detailed and useful. There is a pdf version as well to download 🙂

https://webhostinggeeks.com/guides/dns/

Thanks to Andrijana Nikolic for providing a valuable resource to share with you all.

virsh – show ip address of all running VMs

If you are using the libvirt and associated tools, then you must be aware about virt-manager. However this being a GUI tools, it is not possible to always use this. “virsh” is a good option for this.

To start with, if you need to know all the VMs all the running VMs, then you can use (to only view the names):

virsh list --name

Extending this to make it more useful is the case if you need to know the IP address for the running VMs. Here is a simple code that you can put in alias or function that can be used to get the IP address of the running VM’s.

image ordering by Original Date Time using bash script

Here is the script:

#!/bin/bash -
#===============================================================================
#
#          FILE: imgOrg.sh
#
#         USAGE: ./imgOrg.sh
#
#   DESCRIPTION:
#
#       OPTIONS: ---
#  REQUIREMENTS: ---
#          BUGS: ---
#         NOTES: ---
#        AUTHOR: Amit Agarwal (aka)
#      REVISION:  ---
#===============================================================================

for i in *
do
    if [[ $(file $i) == *image* ]] 
    then
        echo "Image file is :: $i"
        dir=$( exiftool -s -DateTimeOriginal $i | awk -F':' '{print $2"/"$3}')
        mkdir -p $dir
        cp $i $dir/
    else
        echo "Excluding $i"
    fi
done

Disk usage by file type

Trying to find the total usage for each of the file types by extension, then here is a quick bash function for you :

disk_usage_type () 
{ 
    find . -name '*'$1 -ls | awk '
    BEGIN{
        a[0]="Bytes";
        a[1]="KB";
        a[2]="MB";
        a[3]="GB";
    }
    {sum+=$7; files++;}
    END{
    print "Total sum is ::\t" sum;
    print "Total files  ::\t" files;
        while (sum > 1024) {
            sum=sum/1024;
            count++;
            };
        print sum" "a[count];
    }'
}

Just define the function in one of your bash startup files. After that to use the function pass in the extension for which you would like to find the total size. Output should be something like below: