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

open /etc/security/limits.conf as root user
Write the following lines at the bottom of the page.
```
<Username>	hard	nproc		unlimited
<Username>	soft	nproc		unlimited
```
Replace <Username> with original user name.
Restart the machine.

To change maximum file handles per user

open /etc/security/limits.conf as root user
Write the following lines at the bottom of the page.
```
<Username>	hard	nofile		unlimited
<Username>	soft	nofile		unlimited 
```
Replace <Username> with original user name.
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:

Hard Drive
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:

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

# mkswap /dev/sdc1
Enable the swap partition for usage using swapon command:

# swapon /dev/sdc1
Add the following line to the /etc/fstab file to make the swap space partition available even after the reboot:
# cat /etc/fstab
```
/dev/sdc1			swap			swap			defaults			0 0
```

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

# swapon -s

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

		      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.

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
```
1024+0 records in
1024+0 records out
```
Check the user permissions set in the file using the following command:
# ls -l /root/myswapfile
```
-rw-r--r--		 1 root			root			1073741824	 Aug 14 23:47 /root/myswapfile
```
Create Root Permission, that is, change the permission of the swap file so that only root can access it.
# chmod 600 /root/myswapfile
Make this file as a swap file using mkswap command:
# mkswap /root/myswapfile
```
Setting up swapspace version 1, size = 1073737 kB
```
Enable the newly created swapfile.
# swapon /root/myswapfile
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
```
/dev/sdc1			swap			swap			defaults			0 0
```

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

# swapon -s

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

		      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