Managing Linux System-level Configuration

While using Linux/Unix OS, there are various configurations that may be changed to optimize the availability of resources to Fiorano. Below sections discuss the various configuration options.

To change maximum processes per user

1. open /etc/security/limits.conf as root user

2. Write the following lines at the bottom of the page.

   CODE

   <Username>	hard	nproc		unlimited
   <Username>	soft	nproc		unlimited

   

   Replace <Username> with original user name.

3. Restart the machine.

To change maximum file handles per user

1. open /etc/security/limits.conf as root user

2. Write the following lines at the bottom of the page.

   CODE

   <Username>	hard	nofile		unlimited
   <Username>	soft	nofile		unlimited 

   

   Replace <Username> with original user name.

3. Restart the machine.

Checking the Swap Size

# free -k

The command free is used to know how much swap space is currently used by the system. It displays the memory details in KB.

Following is a sample output resulting from free -k command:

		      total	   used      free	shared	buffers	  cached
Mem:		3082356	2043700   1038656	  	 0	  50976	 1646268
-/+ buffers/cache: 	 346456   2735900
Swap:		4192956       0	  4192956 

# swapon -s

Swapon command with option -s displays the current swap size in KB and the file name.

Following is a sample output resulting from swapon -s command:

	 Filename			    Type           Size   		  Used 		   Priority
    /dev/sda2    	  partition    	   4192956 				0    		    -1 

# cat /proc/swaps

This command is same as the swapon -s command, which gives the same output:

	 Filename			    Type           Size   		  Used 		   Priority
    /dev/sda2    	  partition    	   4192956 				0    		    -1 

Increasing the swap size

Additional Swap Space can be created using a:

1. Hard Drive
2. File

Both the methods are explained in the below sections.

Using a Hard Drive Partition

If you have an additional hard disk (or space available in an existing disk), create a partition using fdisk command.

Assume that the partition created is: /dev/sdc1 and perform the following actions:

1. Setup this newly created partition as swap area using the mkswap command:

   # mkswap /dev/sdc1
    

2. Enable the swap partition for usage using swapon command:

   # swapon /dev/sdc1
    

3. Add the following line to the /etc/fstab file to make the swap space partition available even after the reboot:
   # cat /etc/fstab

   CODE

   /dev/sdc1			swap			swap			defaults			0 0

4. Verify whether the newly created swap area is available for your requirement using swapon and free commands:

   # swapon -s 

   Sample Output for # swapon -s command

   CODE

   Filename		     Type 	 	   Size 		 Used	      Priority
   /dev/sda2		partition 		4192956 			0 				-1
   /dev/sdc1		partition 		1048568 			0 				-2

   

   In the output of swapon -s command, the Type column will say "partition" if the swap space is created from a disk partition.

   # free -k

   Sample Output for # free -k command

   CODE

   		      total	     used    free	shared	buffers   cached
   Mem:		3082356	  3022364   59992	  	 0	  55056	 2645472
   -/+ buffers/cache: 	 323836   2758520
   Swap:		5241524       0	  5241524 

Using a File

If you do not have any additional disks, create a file somewhere on your file system and use that file for swap space.

1. Create a swap file with the name "myswapfile" under /root  directory with a size of 1024MB (1GB) using the following dd command:
   # dd if=/dev/zero of=/root/myswapfile bs=1M count=1024

   CODE

   1024+0 records in
   1024+0 records out

2. Check the user permissions set in the file using the following command:
   # ls -l /root/myswapfile

   CODE

   -rw-r--r--		 1 root			root			1073741824	 Aug 14 23:47 /root/myswapfile

3. Create Root Permission, that is, change the permission of the swap file so that only root can access it.
   # chmod 600 /root/myswapfile
 

4. Make this file as a swap file using mkswap command:
   # mkswap /root/myswapfile

   mkswap command output

   CODE

   Setting up swapspace version 1, size = 1073737 kB

5. Enable the newly created swapfile.
   # swapon /root/myswapfile
 

6. To make this swap file available as a swap area even after the reboot, add the following line to the /etc/fstab file using command:
   # cat /etc/fstab

   CODE

   /dev/sdc1			swap			swap			defaults			0 0

7. Verify whether the newly created swap area is available for your requirement using swapon and free commands:

   # swapon -s 

   Sample Output for # swapon -s command

   CODE

   Filename		     Type 	 	   Size 		 Used	      Priority
   /dev/sda2		partition 		4192956 			0 				-1
   /dev/sdc1		partition 		1048568 			0 				-2

   

   In the output of swapon -s command, the Type column will say "file" if the swap space is created from a swap file. 

   # free -k

   Sample Output for # free -k command

   CODE

   		      total	     used    free	shared	buffers   cached
   Mem:		3082356	  3022364   59992	  	 0	  55056	 2645472
   -/+ buffers/cache: 	 323836   2758520
   Swap:		5241524       0	  5241524 

If you don't want to reboot to verify whether the system takes all the swap space mentioned in the /etc/fstab, you can do the following, which will disable and enable all the swap partition mentioned in the /etc/fsta:

swapoff -a

swapon -a