How to Add SWAP file

Linux RAM is composed of chunks of memory called pages. To free up pages of RAM, a “Linux swap” can occur and a page of memory is copied from the RAM to preconfigured space on the hard disk. Linux swaps allow a system to harness more memory than was originally physically available.
However, swapping does have disadvantages. Because hard disks have a much slower memory than RAM, virtual private server performance may slow down considerably. Additionally, swap thrashing can begin to take place if the system gets swamped from too many files being swapped in and out.
Check for Swap Space
Before we proceed to set up a swap file, we need to check if any swap files have been enabled on the VPS by looking at the summary of swap usage.
Swapon –s
An empty list will confirm that you have no swap files enabled:
Filename Type size used Priority
/dev/sda1 partition 7834620 7092 -1
Check the File System :
After we know that we do not have a swap file enabled on the server, we can check how much space we have on the server with the df command. The swap file will take 512MB— since we are only using up about 8% of the /dev/sda, we can proceed.
root@sadeek:/# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda5 236082692 16924872 207339736 8% /
udev 1854004 4 1854000 1% /dev
tmpfs 758308 824 757484 1% /run
none 5120 0 5120 0% /run/lock
none 1895768 80 1895688 1% /run/shm
Create and Enable the Swap File :-


Now it’s time to create the swap file itself using the dd command:
dd if=/dev/zero of=/swapfile bs=1024 count=512k

“of=/swapfile” designates the file’s name. In this case the name is swapfile.

Subsequently we are going to prepare the swap file by creating a linux swap area:
mkswap /swapfile

The results display:


Setting up swapspace version 1, size = 524284 KiB
no label, UUID=9932827f-0478-4819-b428-8debb9c43c71

Finish up by activating the swap file:
swapon /swapfile


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

root@sadeek:/# swapon -s
Filename Type Size Used Priority
/dev/sda1 partition 7834620 7092 -1
/swapfile file 524284 0 -2

This file will last on the virtual private server until the machine reboots. You can ensure that the swap is permanent by adding it to the fstab file.


Open up the file:

vi /etc/fstab
Paste in the following line:
/swapfile none swap sw 0 0

To prevent the file from being readable, you should set up the correct permissions on the swap file:


chown root:root /swapfile
chmod 600 /swapfile

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 Execute commands simultaneously on multiple server using PSSH/CLUSTER

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Logrotation in Linux/unix

Log files are the most valuable tools available for Linux system security. The logrotate program is used to provide the administrator with an up-to-date record of events taking place on the system. The logrotate utility may also be used to back up log files, so copies may be used to establish patterns for system use.

logrotate
the logrotate program is a log file manager. It is used to regularly cycle (or rotate) log files by removing the oldest ones from your system and creating new log files. It may be used to rotate based on the age of the file or the file’s size, and usually runs automatically through the cron utility. The logrotate program may also be used to compress log files and to configure e-mail to users when they are rotated.

Configuration File :- 
Files
/var/lib/logrotate.status   >> this file update  status of recent execution of  logrotation.

root@puppet:~/sadeek/big# ls -l /var/lib/logrotate/status
-rw-r--r-- 1 root root 2030 Feb 23 07:55 /var/lib/logrotate/status

root@puppet:/etc/logrotate.d# ls -l /var/lib/logrotate/status

-rw-r--r-- 1 root root 2030 Feb 24 05:57 /var/lib/logrotate/status

Default state file.
/etc/logrotate.conf     by default configuration file of logs
below are the some example for log rotation configuration, you need to create a file and make the entry as below. it will rotate the logs weekly.
/etc/logrotate.d/

 vi samba

/var/log/samba/log.smbd {

        weekly

        missingok

        rotate 7

        postrotate

                reload smbd 2>/dev/null

        endscript

        compress

        notifempty

root@puppet:/etc/logrotate.d# 

for different application you need to create a file and config . we can execute the script with the help of postrotate  you need to mention the script location. 

root@puppet:/etc/logrotate.d#

this job execute by cron.daily  you can cehck the cron.daily entry under the cat /etc/cron.daily file 

 vi test

/root/sadeek/logs/logs.log {

    daily

    rotate 2

    missingok

    copytruncate

    olddir /root/sadeek/big

#    postrotate

#        /bin/sh /root/sadeek/rotate.sh

#    endscript

}

FOR MORE OPTION YOU CAN CHECK THE man logroate