I happen to chance upon a good tutorial on the above topic. Here is the link for the tutorial

RAM is composed of chunks of memory called Pages.  When programs execute, it takes fills up pages. Due to this sooner or later memory will run out. In order to free up the RAM, Pages can be swapped into hard drive and the freed up RAM can be used by the other program which needs CPU’s attention.

Swap space is not a must in Linux. So if you happen to have a system that does not have Swap space, then follow the below guide to create a swap file and use it.

Check whether a SWAP space is enabled

sudo swapon -s

if you do not have swap enabled in the system you should see the output as below

Filename                                Type            Size    Used    Priority

Check the system for available space.

The recommended swap file size is twice the size of the RAM size. If your RAM
size is 512 MB, then the SWAP file size should be 1GB.

df

Filesystem           1K-blocks      Used        Available Use% Mounted on
/dev/vda              20642428   2367536    17226316  13% /
tmpfs                   254432         0                  254432   0% /lib/init/rw
udev                    249612        60                   249552   1% /dev
tmpfs                   254432         4                    254428   1% /dev/shm

Allocate space for swapfile

sudo fallocate -l 1GB  /swapfile

Create Swap file

sudo mkswap /swapfile

the output will look like below

Setting up swapspace version 1, size = 8388608 KiB
no label, UUID=103c4545-5fc5-47f3-a8b3-dfbdb64fd7eb

Turn on the SWAP file

sudo swapon  /swapfile

You will then be able to see the new swap file when you view the swap summary.

swapon -s
Filename				Type		Size	Used	Priority
/swapfile                               file		8388608 0	-1

TO add this partition permanently, add it into /etc/fstab

sudo nano /etc/fstab

/swapfile  none  swap  sw  0  0

save and close the fstab file.

If you want to override a named command in main.cf, normally you can specify in the master.cf as override option (-o) to the command.
There is one quirk here though. It cannot contain any white spaces. The manual page explain this clearly. However, it is silent when it comes to parameter values that contains whitespace. There are no examples as well.

The simple trick here is to replace white space with comma as well.

For example:
….. -o smtpd_client_restrictions=check_client_access,hash:/etc/postfix/access

Please see the comma after check_client_access.

But when you use this parameter in main.cf, it will be as below
smtpd_client_restrictions=check_client_access hash:/etc/postfix/access

We saw a huge monitor lizard while We were on our way to Kuantan in Malaysia . It was heavily raining and the monitor lizard was trying to cross the road.

I happen to bounce on a web based SQL Designer. The tool is hosted at GAE SQL Designer. Using this tool I was able to create relational database tables and normalize it. As this is
Visual design, I was able to visualize the table relationship and normalize it much more easily. The other benefit of this tool is that it allows you to create SQL statements for various databases. It also allows to export in XML.