Step 1: Open a terminal window
# su – or # sudo -s
Step 2: Creation of the Storage File for the new swap file
Type the following command to create 512MB swap file (1024 * 512MB = 524288 block size):
# dd if=/dev/zero of=/swap bs=1024 count=524288
If you don’t want to have to reboot use the following commands:
(This is useful for debugging automout issue)
524288+0 records in 524288+0 records out 536870912 bytes (537 MB) copied, 3.23347 s, 354 MB/s
1. if=/dev/zero : Read from /dev/zero file. /dev/zero is a special file in that provides as many null characters to build storage file called /swap.
2. of=/swap : Read from /dev/zero write storage file to /swapf.
3. bs=1024 : Read and write 1024 BYTES bytes at a time.
4. Count=524288 : Copy only 523288 BLOCKS input blocks.
Step 3 : Secure the new created swap file
Setup the correct file permission:
# chown root:root /swap
# chmod 0600 /swap
A world-readable swap file is a huge local vulnerability.
Step 4: Set up a Centos 7 swap area
Type the following command to set up a Linux swap area in a file:
# mkswap /swap
Sample outputs:
Setting up swapspace version 1, size = 524284 KiB
no label, UUID=0e5e7c60-bbba-4089-a76c-2bb29c0f0839
Step 5: Enabling the swap file
Finally, activate /swap swap space immediately, enter:
# swapon /swapfile1
Step 6: Update /etc/fstab file
To activate /swap after CentOS 7 system reboot, add entry to /etc/fstab file. Open this file using a text editor such as nano:
# nano /etc/fstab
Copy & Paste the following line:
/swap none swap sw 0 0
Save and close the file.
Verify if your swap file is activated?
# free -m
total used free shared buffers cached Mem: 1876 1798 77 0 119 1440 -/+ buffers/cache: 237 1638 Swap: 4607 0 4607
Display swap usage summary
# swapon -s
Filename Type Size Used Priority /dev/sda6 partition 4194296 0 0 /swap file 524280 0 0
Another option is to view /proc/meminfo file:
# less /proc/meminfo
# grep -i –color swap /proc/meminfo
SwapCached: 30748 kB SwapTotal: 6291448 kB SwapFree: 6154008 kB
Optional, test the new swap file:
# swapoff -a
# swapon -a
Enjoy!