How to create swap Partition & check or reduce swap memory

 Creating a Swap Partition:

[root@dev ~]# fdisk /dev/sdb
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p

Disk /dev/sdb: 8589 MB, 8589934592 bytes, 16777216 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x13fe498e

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152   83  Linux
/dev/sdb2         4196352     8390655     2097152   8e  Linux LVM

Command (m for help): n
Partition type:
   p   primary (2 primary, 0 extended, 2 free)
   e   extended
Select (default p): p
Partition number (3,4, default 3): 3
First sector (8390656-16777215, default 8390656):
Using default value 8390656
Last sector, +sectors or +size{K,M,G} (8390656-16777215, default 16777215): +2048M
Partition 3 of type Linux and of size 2 GiB is set

Command (m for help): p

Disk /dev/sdb: 8589 MB, 8589934592 bytes, 16777216 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x13fe498e

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152   83  Linux
/dev/sdb2         4196352     8390655     2097152   8e  Linux LVM
/dev/sdb3         8390656    12584959     2097152   83  Linux

Command (m for help): t
Partition number (1-3, default 3): 3

Hex code (type L to list all codes): 82
Changed type of partition 'Linux' to 'Linux swap / Solaris'

Command (m for help): p

Disk /dev/sdb: 8589 MB, 8589934592 bytes, 16777216 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x13fe498e

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152   83  Linux
/dev/sdb2         4196352     8390655     2097152   8e  Linux LVM
/dev/sdb3         8390656    12584959     2097152   82  Linux swap / Solaris

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
[root@dev ~]# partprobe
[root@dev ~]# mkswap /dev/sdb3
Setting up swapspace version 1, size = 2097148 KiB
no label, UUID=d2fde43f-4e96-42a5-9ac8-8cb7fa6d18c5
[root@dev ~]# swapon /dev/sdb3
[root@dev ~]# swapon -s
Filename                Type        Size    Used    Priority
/dev/dm-1                                  partition    4063228    0    -2
/dev/sdb3                                  partition    2097148    0    -3
 

Check Swap memory 

[root@dev ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:           3789         829         417          33        2542        2648
Swap:          6015           0        6015
 

Reduce Swap memory

[root@dev ~]# swapoff /dev/sdb3
[root@dev ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:           3789         828         417          33        2542        2648
Swap:          3967           0        3967