How to Create SWAP in Centos

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Most Linux installations recommend that you include a SWAP partition. Swap partition is the second type of memory in Linux systems. The primary function of swap is to use disk space for RAM memory when real RAM fills up and more space is needed.

In this article you will learn that how to create swap. There are three types of swap will be covered in this article respectively.

  • Standard SWAP
  • LVM SWAP
  • SWAP File

Create Standard SWAP

Command to see available RAM and SWAP stats

# free -h

# swapon -s

Step 1: Follow below instructions

  • List partition table using below command

    # fdisk -l
  • Choose desired hard disk for swap partition List partition table using below command
    # fdisk /dev/sdb
  • Press m for help
  • Press p to print partition table
  • Press n to create new partition
  • Press p to make primary partition.
  • Press 1 to create first partition on selected disk.
    There are 1-4 partition number. We can type any one number from them.
  • Press enter to leave first cylinder as default
  • Now assign space to partition. Use + to assign space e.g.
    +1G and press enter.
  • Press p to print partition table.
  • Now set SWAP file system ID on partition.
  • Press l to list all available file system volumes. We will set SWAP (82)
  • Press t to set file system on partition
  • Press 1 to select partition. It is the partition on which we set SWAP file system.
  • type 82 and press enter to set LVM ID on selected partition.
  • Press w to write/save partition.

Now run command to make changes in partition table using below command

# partprobe

 

Step 2: Format Partition (File System)

# mkswap   /dev/sdb1

 

Step 3: Set Partition Label

Command to set Label on SWAP Partition
Syntax:  mkswap   -L   Label-name    /dev/partition

# mkswap   -L   myswap    /dev/sdb1

 

Step 4: Now Mount partition in /etc/fstab File

# vim /etc/fstab

and add following entry:

LABEL=myswap           swap    swap    deafults    0     0

write changes to /etc/fstab and quite

 

Step 5: Now Activate Created SWAP

# swapoff  -a              (Disable all swap)

# swapon  -a               (enable all swap)

# swapon  -s               (list enabled all swap)

# free   -m

You have created standard swap successfully!


LVM SWAP

Step 1: Follow Previous procedure

Step 2: Follow Previous procedure

Step 3: Create PV (Physical Volume) of the partition

Use below command

#pvcreate   /dev/sdb1

#pvs

Step 4: Create VG (Volume Group)

#vgcreate   swap_vg    /dev/sdb1

#vgs

Note: swap_vg is vg name you can use any

Step 5: Create LVM (Logical Volum Manager)

Use below command

# lvcreate   -l   100%free   -n    swap_lvm   swap_vg
# lvs

swap_lvm   is the LVM Name. you can use any.

swap_vg     is the name of created VG

Step 6: Format Partition (File system)

# mkswap   /dev/swap_vg/swap_lvm

Step 7: Mount Partition in /etc/fstab File

# vi /etc/fstab

and add following entry:

/dev/swap_vg/swap_lvm  swap  swap  defaults 0 0

write changes to /etc/fstab and quite

Step 8: Now Activate Created SWAP

# swapoff  -a              (Disable all swap)

# swapon  -a               (enable all swap)

# swapon  -s               (list enabled all swap)

# free   -m

Make SWAP FILE

Step 1: Make File

We will create swap file of 3GB

Use following command

# dd if=/dev/zero of=/myswap bs=1G count=3

Note: Above command will take some time to generate the file.

Step 2: Set Permission on SWAP File

set the appropriate permissions on the file to make it readable only by root user.

# cd /

# chmod   600   /myswap

# ls –lh myswap

Step 3: Set SWAP Filesystem on file

# mkswap /myswap

Step 4: Enable SWAP File

# swapon  /myswap

Step 5: Mount SWAP File in /etc/fstab file

# vi /etc/fstab

and add following entry:

/myswap  swap  swap  defaults 0 0

write changes to /etc/fstab and quite

Step 6: Now Activate Created SWAP

# swapoff  -a              (Disable all swap)

# swapon  -a               (enable all swap)

# swapon  -s               (list enabled all swap)

# free   -m

You have learn that how to create different types of SWAP in Linux.

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