Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Programming
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Databases
Mail Systems
openSolaris
Eclipse Documentation
Techotopia.com
Virtuatopia.com

How To Guides
Virtualization
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Windows
Problem Solutions

  




 

 

NOTE: CentOS Enterprise Linux 5 is built from the Red Hat Enterprise Linux source code. Other than logo and name changes CentOS Enterprise Linux 5 is compatible with the equivalent Red Hat version. This document applies equally to both Red Hat and CentOS Enterprise Linux 5.

5.2. Adding Swap Space

Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 128 MB to 256 MB, but there is only 256 MB of swap space. It might be advantageous to increase the amount of swap space to 512 MB if you perform memory-intense operations or run applications that require a large amount of memory.

You have three options: create a new swap partition, create a new swap file, or extend swap on an existing LVM2 logical volume. It is recommended that you extend an existing logical volume.

5.2.1. Extending Swap on an LVM2 Logical Volume

To extend an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):

  1. Disable swapping for the associated logical volume:

    # swapoff -v /dev/VolGroup00/LogVol01
    
  2. Resize the LVM2 logical volume by 256 MB:

    # lvm lvresize /dev/VolGroup00/LogVol01 -L +256M
    
  3. Format the new swap space:

    # mkswap /dev/VolGroup00/LogVol01
    
  4. Enable the extended logical volume:

    # swapon -va
    
  5. Test that the logical volume has been extended properly:

    # cat /proc/swaps # free
    

5.2.2. Creating an LVM2 Logical Volume for Swap

To add a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want to add):

  1. Create the LVM2 logical volume of size 256 MB:

    # lvm lvcreate VolGroup00 -n LogVol02 -L 256M
    
  2. Format the new swap space:

    # mkswap /dev/VolGroup00/LogVol02
    
  3. Add the following entry to the /etc/fstab file:

    /dev/VolGroup00/LogVol02   swap     swap    defaults     0 0
    
  4. Enable the extended logical volume:

    # swapon -va
    
  5. Test that the logical volume has been extended properly:

    # cat /proc/swaps # free
    

5.2.3. Creating a Swap File

To add a swap file:

  1. Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 64 MB swap file is 65536.

  2. At a shell prompt as root, type the following command with count being equal to the desired block size:

    dd if=/dev/zero of=/swapfile bs=1024 count=65536
    
  3. Setup the swap file with the command:

    mkswap /swapfile
    
  4. To enable the swap file immediately but not automatically at boot time:

    swapon /swapfile
    
  5. To enable it at boot time, edit /etc/fstab to include the following entry:

    /swapfile          swap            swap    defaults        0 0
    

    The next time the system boots, it enables the new swap file.

  6. After adding the new swap file and enabling it, verify it is enabled by viewing the output of the command cat /proc/swaps or free.


 
 
  Published under the terms of the GNU General Public License Design by Interspire