Linux – What file system is swap on Linux

filesystemslinuxpartitioningswapUbuntu

In Linux you can choose things like ext3 and reiserfs for partitions. For the swap partition, you just choose "swap." What file system is this, actually? Can you just create an ext3 partition and make it a swap partition? How would that be different?

Best Answer

Swap is no actual file system. It is just a reserved part of the disk that is raw addressable memory with no special structure.

mkswap creates a header for the swap area with some additional information. From swapheader.h of the util-linux-ng package:

struct swap_header_v1 {
    char         bootbits[1024];    /* Space for disklabel etc. */
    unsigned int version;
    unsigned int last_page;
    unsigned int nr_badpages;
    unsigned int padding[125];
    unsigned int badpages[1];
};

Header version 1 is the currently used one. Thats about all the magic behind the raw structure of swap.

Related Solutions

Linux – Changing Linux swap partition

This is in case you don't find a GUI method, you will find the terminal method quite flexible and easy. Run the following commands:

sudo swapoff /dev/hda3
sudo mkswap /dev/hda4
sudo swapon /dev/hda4

Then update /etc/fstab. Change the line containing "/dev/hda3" to "/dev/hda4".

Here is the Ubuntu page on Swap FAQ. Also note (from that page):
With the 2.6 kernel, "a swap file is just as fast as a swap partition."
^{Which means that you don't need to lock down a partition for swap space; you can tune it locally in a data partition as a swap-file.}

Linux – swap partition

The main ideas before you dive into some guides if you feel like it to learn more details:

What is

It's a special type of partition (sometimes OSes simply use one giant swap file).

What is for

The swap partition is used by an OS to artificially increase the size of the memory.

When should I use

When you think that the size of your physical memory (a.k.a. RAM) won't to be enough to run all the programs you plan to use.

Why should I use

Because you don't want programs to crash because they are out of memory.

Pros/ Cons to add this to system

Pro: artificially increase the size of the memory, meaning that you could run more programs that you have done without it.
Con: disks much slower than RAM

Best Answer

Related Solutions

Linux – Changing Linux swap partition

Linux – swap partition

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