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?

Fix fonts quickly with auto-hinting

Very quick hack to fix the font hinting automatically. Just execute the below:

sudo ln -s /usr/share/fontconfig/conf.avail/10-autohint.conf /etc/fonts/conf.d/10-autohint.conf

After this you should see the font hinting enabled and thus better experience with fonts.

Get your local IP address like pro

In shell scripts if you need to get you local IP address corresponding to your hostname then you can use this command

hostname -i

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web services in c with cgi

I was trying to setup a simply webservice to reply to POST requests. Earlier this was being done in tomcat which seem a little overkill to me since I already had a webserver up and running. So, a quick c program to respond to request is all that I needed. And here is the result.

/*
 * =====================================================================================
 *
 *       Filename:  Login.cpp
 *
 *    Description:
 *
 *        Version:  1.0

 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Amit Agarwal (),
 *   Organization:
*
* == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == == =
    */
#include <stdio .h>
#include <stdlib .h>
#include <string .h>


#define MAXLEN 1024

#ifdef DBG
#define DEBUG(a,b) fprintf(stderr, a, b);
#else
#define DEBUG(a,b) 
#endif

#define HEAD "n"
#define TAIL ""

int main(void)
{

    char input[MAXLEN];
    char * data;
    char*lenstr;
    long len;


    printf("%s%c%cnn",
           "Content-Type:text/xml;charset=iso-8859-1", 13, 10);

    // len = getenv("QUERY_STRING"); // This is for GET
    lenstr = getenv("CONTENT_LENGTH");
    DEBUG( "Length string is %sn", lenstr);

    if(lenstr == NULL || sscanf(lenstr,"%ld",&len)!=1 || len > MAXLEN)
        printf("Error in invocation - wrong FORM probably.");
DEBUG( "Length is %ldn", len);
{
int count=0;
while ( count < len )
input[count++] = getchar();
input[count]='?';
DEBUG ( "Read characters = %dn", count)
}

//fprintf(stderr, "VAlue is %sn", input);
///unencode(input + 5 , input + len, data);

data = input;
DEBUG("Data value is %sn", data);

printf(HEAD);
printf("Everything else goes heren");
printf(TAIL);

fprintf(stderr, "Sent resp: tid[%s], eaid[%s], tcode[%s]n", tid, eaid, tcode);
}
</string></stdlib></stdio>

Additionally, the makefile:

firewalld – enable logging

firewalld by default does not allow packets that are dropped. In some cases, you need to find out if some packet is being dropped or not. For doing so you may want to enable logging of dropped packets with the following command:

sudo firewall-cmd  --set-log-denied=all

This will enable logging all the packets and help you figure out if firewalld is dropping the packet.

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:

Get count of lines in scripts (shell)

If you have tried to get the count of lines in file, the you would know about “nl” or “wc -l”. But as you are aware these give you number of lines with other details as well and you need to post process the number to make sure that you have only number and nothing else. In such cases, it is useful to use the count feature of grep and here is a shorthand to get the count of lines in any shell script: