How to Add Virtual Memory In Linux

2017-09-18

Linux, Ubuntu

Server environment

1 2	$ cat /etc/issue Ubuntu 14.04.5 LTS

View the memory

$ free -h

             total       used       free     shared    buffers     cached
Mem:          2.0G       243M       1.7G       424K        11M       145M
-/+ buffers/cache:        86M       1.9G
Swap:         0B          0B        0B

As shown, the memory is 2G.

Use the dd command to create a file swapfile with a size of 2G：

1	$ dd if=/dev/zero of=/mnt/swapfile bs=1M count=2048

“if” means input_file, “of” means output_file, “bs” means block_size, “count” means counting way. Here, I used the data block size 1M, the number of data blocks 2048, so that the allocation of space is 2G size.

Format the swap file：

1	$ mkswap /mnt/swapfile

1 2	Setting up swapspace version 1, size = 2 GiB (2147479552 bytes) no label, UUID=e509fbd9-f640-446d-9261-180f2bdb444c

Mount the swap file：

1	$ swapon /mnt/swapfile

1	swapon: /mnt/swapfile: insecure permissions 0644, 0600 suggested.

In this way, you can see the memory size after adding 2G virtual memory, as shown in the figure, a total of 4G.

$ free -h

             total       used       free     shared    buffers     cached
Mem:          2.0G       243M       1.7G       424K        11M       145M
-/+ buffers/cache:        86M       1.9G
Swap:         2.0G         0B       2.0G

Modify the configuration file, automatically load virtual memory after boot

1	$ sudo vim /etc/fstab

Add the following command to the /etc/fstab file：

1	/mnt/swapfile swap swap defaults 0 0

Ok ,the tutorial has been done.

Change swap size to 8G

$ sudo swapoff -a
$ dd if=/dev/zero of=/mnt/swapfile bs=1M count=8192
$ mkswap /mnt/swapfile
$ swapon /mnt/swapfile

If you use a period of time, the free memory becomes less and less, you can try to release some spare memory space

1
2
3

$ sync
$ su
$ echo 3 > /proc/sys/vm/drop_caches