Swap memory setup - Ubuntu 12.04 LTS

Problem statement

I hosted a website in a VPS. I installed apache2, mysql, mail system (postfix + dovecot + spamassisn) etc.
So far it was working fine. Next I enabled SSL for that site. Hopefully after that memory demand in system increased.
And very often I found MySQL aborting. On checking error log (in /var/log/mysql/error.log), I found while allocating memory for InnoDB buffer pool, memory allocation fails.

InnoDB: Initializing buffer pool, size = 128.0M
InnoDB: mmap(137363456 bytes) failed; errno 12
InnoDB: Completed initialization of buffer pool
InnoDB: Fatal error: cannot allocate memory for the buffer pool
[ERROR] Plugin 'InnoDB' init function returned error.
[ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
[ERROR] Unknown/unsupported storage engine: InnoDB
[ERROR] Aborting

My VPS RAM is just 512M, hence this is crashing. So as a first step I deleted below files.

rm /var/lib/mysql/ib_logfile0
rm /var/lib/mysql/ib_logfile1

Though it reduced frequent MySQL crash, still it was crashing at times.

So I thought lets add swap memory. With this, this problem was resolved.

What is swap memory?

If your system memory (RAM) is less, and you are running multiple applications then you are under risk of memroy allocation failures. This issue can be resolved by making use of swap memory, but at a cost of reduced performance. The below steps are followed for increasing swap memory in a linux machine.


OS: Ubuntu 12.04 LTS 64 bit


Please follow below steps to allocate swap memory in your machine.

  1. Login as root to system
  2. Execute below command to see if swap space is allocated previously
    swapon -s

    If no swap space allocated, you will get empty list like

    Filename        Type      Size      Used      Priority
  3. Now you are sure, swap file is not present.
  4. Chedk disk size using df command and check system memory (HD) and decide how much swap memory you would like add.

    The ouput is as below

    /dev/vda1      20511356      4861172      14585224      25%      /
    udev      240064      8      240056      1%      /dev
    tmpfs      50184      236      49948      1%      /run
    none      5120      0      5120      0%      /run/lock
    none      250908      0      250908      0%      /run/shm
  5. So I decided to allocate 2GB of swap memory. Say I want to name the swap file as swapfile.
    dd if=/dev/zero of=/swapfile bs=1024 count=2048k
    mkswap /swapfile
    swapon /swapfile
    swapon -s

    With this, your system swap memory is set as 2GB.
    Hold on, if you restart your system it may go off. If you want to make it permanent the execute

    vi /etc/fstab

    Add below line of code to /etc/fstab file (at the end of file)

    /swapfile none swap sw 0 0
  6. Execute
    echo 10 | sudo tee /proc/sys/vm/swappiness
    echo vm.swappiness = 10 | sudo tee -a /etc/sysctl.conf
    chown root:root /swapfile
    chmod 0600 /swapfile
  7. Next you can verify if swap memory is available by executing
    free -m

    Output looks as below

    total used free shared buffers cached
    Mem: 490 476 13 0 4 42
    -/+ buffers/cache: 429 60
    Swap: 2047 0 2047

    You can see swap line above.