Linux RAM is composed of chunks of memory called pages. To free up pages of RAM, a \u201clinux swap\u201d can occur and a page of memory is copied from the RAM to preconfigured space on the hard disk. Linux swaps allow a system to harness more memory than was originally physically available.<\/p>\n
However, swapping does have disadvantages. Because hard disks have a much slower memory than RAM, virtual private server performance may slow down considerably. Additionally, swap thrashing can begin to take place if the system gets swamped from too many files being swapped in and out.<\/p>\n
Before we proceed to set up a swap file, we need to check if any swap files have been enabled on the VPS by looking at the summary of swap usage.<\/p>\n
sudo swapon -s<\/pre>\nAn empty list will confirm that you have no swap files enabled:<\/p>\n
Filename\t\t\t\tType\t\tSize\tUsed\tPriority<\/pre>\nCheck the File System<\/h2>\n
After we know that we do not have a swap file enabled on the virtual server, we can check how much space we have on the server with the\u00a0
df<\/code>\u00a0command. The swap file will take 512MB and since we are only using up about 8% of the \/dev\/sda, we can proceed.<\/p>\ndf\r\nFilesystem 1K-blocks Used Available Use% Mounted on\r\n\/dev\/sda 20907056 1437188 18421292 8% \/\r\nudev 121588 4 121584 1% \/dev\r\ntmpfs 49752 208 49544 1% \/run\r\nnone 5120 0 5120 0% \/run\/lock\r\nnone 124372 0 124372 0% \/run\/shm<\/pre>\nCreate and Enable the Swap File<\/h2>\n
Now it\u2019s time to create the swap file itself using the dd command :<\/p>\n
sudo dd if=\/dev\/zero of=\/mnt\/swap bs=1024 count=512k<\/pre>\n\n
- if=\/dev\/zero\u00a0<\/em>means input file. In this case it’s linux zero-generator<\/li>\n
- of=\/mnt\/swap<\/em>\u00a0specifies output file name. In this case the name is \/mnt\/swap.<\/li>\n
- bs <\/em>means the block size allocated in bytes (1024b)<\/li>\n
- count\u00a0<\/em>is the number how many blocks of bs <\/em>size will be allocated (512 000 * 1024b)<\/li>\n<\/ul>\n
Subsequently we are going to prepare the swap file by creating a linux swap area:<\/p>\n
sudo mkswap \/mnt\/swap<\/pre>\nThe results display:<\/p>\n
Setting up swapspace version 1, size = 262140 KiB\r\nno label, UUID=103c4545-5fc5-47f3-a8b3-dfbdb64fd7eb<\/pre>\nFinish up by activating the swap file:<\/p>\n
sudo swapon \/mnt\/swap<\/pre>\nYou will then be able to see the new swap file when you view the swap summary.<\/p>\n
swapon -s\r\nFilename\t\t\t\tType\t\tSize\tUsed\tPriority\r\n\/mnt\/swap file\t\t262140\t0\t-1<\/pre>\nThis file will last on the virtual private server until the machine reboots. You can ensure that the swap is permanent by adding it to the fstab file.
\nOpen up the file:<\/p>\nsudo nano \/etc\/fstab<\/pre>\nPaste in the following line:<\/p>\n
\/mnt\/swap none swap sw 0 0<\/pre>\nTo prevent the file from being world-readable, you should set up the correct permissions on the swap file:<\/p>\n
sudo chown root:root \/mnt\/swap \r\nsudo chmod 0600 \/mnt\/swap<\/pre>\n","protected":false},"excerpt":{"rendered":"Linux RAM is composed of chunks of memory called pages. To free up pages of RAM, a \u201clinux swap\u201d can occur and a page of memory is copied from the RAM to preconfigured space on the hard disk. Linux swaps … Continue reading