How to increase SWAP Memory in Centos 7
To increase SWAP Memory in Centos 7
Swap space is used when the physical memory (RAM) is full.Swap memory increases the efficiency of Ram. This tutorial explains how to increase SWAP memory in Linux after installation.
There are two methods to increase the swap memory after installation.
1. fdisk utility
To check the system for swap information, use swapon -s option.
[root@linuxhelp ~]# swapon -s
Filename Type Size Used Priority
/dev/sda2 partition 2047996 25348 -1
To view the system' s overall memory usage, execute the following command.
[root@linuxhelp ~]# free -m
total used free shared buffers cached
Mem: 987 837 149 5 0 191
-/+ buffers/cache: 646 340
Swap: 1999 24 1975
Before allocating swap, check the space availability of drive using the following command.
[root@linuxhelp ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 15G 8.5G 6.3G 58% /
devtmpfs 486M 0 486M 0% /dev
tmpfs 494M 140K 494M 1% /dev/shm
tmpfs 494M 7.1M 487M 2% /run
tmpfs 494M 0 494M 0% /sys/fs/cgroup
/dev/sda1 297M 106M 192M 36% /boot
Create partition for swap space using the following command.
[root@linuxhelp ~]# fdisk /dev/sda 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. To create new partition type n press enter If free space is available, fdisk normally starts the new partition at the first available sector or cylinder. The actual size of the partition depends on disk geometry. Press enter of First cylinder line Command (m for help): n Partition type: p primary (3 primary, 0 extended, 1 free) e extended Select (default e): ----------------------------------------> Press enter select default partition type Using default response e Selected partition 4 First sector (35432448-41943039, default 35432448): ---------------> Press enter select default First sector value Using default value 35432448 Last sector, +sectors or +size{K,M,G} (35432448-41943039, default 41943039):-------> Press enter to select full hard disk space Using default value 41943039 Partition 4 of type Extended and of size 3.1 GiB is set Press “ n” to create a new partition Command (m for help): n All primary partitions are in use Adding logical partition 5 First sector (35434496-41943039, default 35434496): Using default value 35434496 Last sector, +sectors or +size{K,M,G} (35434496-41943039, default 41943039): +100M Partition 5 of type Linux and of size 100 MiB is set Command (m for help): p Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 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: 0x000b1397 Device Boot Start End Blocks Id System /dev/sda1 * 2048 616447 307200 83 Linux /dev/sda2 616448 4712447 2048000 82 Linux swap / Solaris /dev/sda3 4712448 35432447 15360000 83 Linux /dev/sda4 35432448 41943039 3255296 5 Extended /dev/sda5 35434496 35639295 102400 83 Linux Command (m for help): l 0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris 1 FAT12 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT- 2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT- 3 XENIX usr 3c PartitionMagic 84 OS/2 hidden C: c6 DRDOS/sec (FAT- 4 FAT16 < 32M 40 Venix 80286 85 Linux extended c7 Syrinx 5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data 6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / . 7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility 8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt 9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi eb BeOS fs e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD ee GPT f W95 Ext' d (LBA) 54 OnTrackDM6 a6 OpenBSD ef EFI (FAT-12/16/ 10 OPUS 55 EZ-Drive a7 NeXTSTEP f0 Linux/PA-RISC b 11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f1 SpeedStor 12 Compaq diagnost 5c Priam Edisk a9 NetBSD f4 SpeedStor 14 Hidden FAT16 < 3 61 SpeedStor ab Darwin boot f2 DOS secondary 16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ fb VMware VMFS 17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE 18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto 1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep 1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT 1e Hidden W95 FAT1 80 Old Minix Press “ t” to change the type of system Command (m for help): t Partition number (1-5, default 5): 5 Hex code (type L to list all codes): 82 Changed type of partition ' Linux' to ' Linux swap / Solaris' Press “ p” to list the partition Command (m for help): p Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 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: 0x000b1397 Device Boot Start End Blocks Id System /dev/sda1 * 2048 616447 307200 83 Linux /dev/sda2 616448 4712447 2048000 82 Linux swap / Solaris /dev/sda3 4712448 35432447 15360000 83 Linux /dev/sda4 35432448 41943039 3255296 5 Extended /dev/sda5 35434496 35639295 102400 82 Linux swap / Solaris Press “ w” to save command 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.
Then refresh the system settings, using the partprobe command.
[root@linuxhelp ~]# partprobe /dev/sda
Format the swap partition by using mkswap command
[root@linuxhelp ~]# mkswap /dev/sda5
Setting up swapspace version 1, size = 102396 KiB
no label, UUID=3351f2e7-0cca-4d7c-9a11-1ca982d81f03
Activate the swap partition by using the following command.
[root@linuxhelp ~]# swapon /dev/sda5
To verify whether the new swap volume is recognised, run the following command.
[root@linuxhelp ~]# cat /proc/swaps
Filename Type Size Used Priority
/dev/sda2 partition 2047996 25312 -1
/dev/sda5 partition 102396 0 -2
Open the /etc/fstab configuration file.
[root@linuxhelp ~]# vim /etc/fstab
Add the following entry at the end of the file.
/dev/sda5 swap swap defaults 0 0
Save and exit the file.
Restart the system.
[root@linuxhelp ~]# reboot &ndash f
After rebooting the system, verify whether swap is working properly or not
[root@linuxhelp ~]# cat /proc/swaps
Filename Type Size Used Priority
/dev/sda2 partition 2047996 102396 0 -1
/dev/sda5 partition 102396 0 2047996 0 -2
2. File method
If no additional disks is available, create a file and use that file for swap space.
Utilize the following command to create a swap file under /root directory.
[root@linuxhelp ~]# dd if=/dev/zero of=/root/myswap bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 24.8354 s, 43.2 MB/s
[root@linuxhelp ~]# ls -l /root/myswap
-rw-r--r--. 1 root root 1073741824 Jul 6 06:32 /root/myswap
Change the permission of the swap file.
[root@linuxhelp ~]# chmod 600 /root/myswap [root@linuxhelp ~]# ls -l /root/myswap -rw-------. 1 root root 1073741824 Jul 6 06:32 /root/myswap
Make the file as a swap file using mkswap command.
[root@linuxhelp ~]# mkswap /root/myswap
Setting up swapspace version 1, size = 1048572 KiB
no label, UUID=499cf292-9daa-49de-a621-2f9143e59179
Enable the newly created swap file
[root@linuxhelp ~]# swapon /root/myswap
Now add the entry in the /etc/fstab configuration file.
[root@linuxhelp ~]# vim /etc/fstab
Add the following at the end of the file.
/root/myswap swap swap defaults 0 0
Save and exit from the file.
Verify whether the newly created swap area is available or not.
[root@linuxhelp ~]# swapon -s
Filename Type Size Used Priority
/dev/sda5 partition 102396 5128 -1
/dev/sda2 partition 2047996 0 -2
/root/myswap file 1048572 0 -3
[root@linuxhelp ~]# free -m
total used free shared buffers cached
Mem: 987 835 151 4 0 323
-/+ buffers/cache: 512 474
Swap: 3123 5 3118
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How to Optimizing Swap performance?
A
Because swap space uses a disk device, this can cause performance issues in any system that uses swap space significantly because the system itself may also be using the same disk device at t
Activating the swap partition,
Making the new swap partition work for hibernate (optional)