Two commands to create swap partition

The swap partition is used to retain the contents of memory when physical memory (RAM) is filled. When RAM is exhausted, Linux will move inactive pages in memory to swap space, thereby freeing up memory for the system to use. Nonetheless, swap space should not be considered a substitute for physical memory.

In most cases, it is recommended that the swap memory size be 1 to 2 times the physical memory. This means that if you have 8GB of memory, the swap space size should be between 8-16 GB.

If there is no swap partition configured in the system, when the memory is exhausted, the system may kill the running processes/applications, causing the system to crash. In this article, we will learn how to add a swap partition to a Linux system. We have two methods:

• Use fdisk command
• Use fallocate command

The first method (using the fdisk command)

Usually, the first hard disk of the system will be named /dev/sda, and the partitions will be named /dev/sda1, /dev/ sda2. In this article, we use a hard disk with two primary partitions. The two partitions are /dev/sda1 and /dev/sda2, and we use /dev/ sda3 is used as a swap partition.

First create a new partition,

$ fdisk /dev/sda

Press n to create a new partition. The system will ask you which cylinder to start from, just press Enter to use the default value. The system then asks you which cylinder you want to end on, here we enter the size of the swap partition (for example, 1000MB). Here we enter 1000M.

swap

Now we have created a disk with a size of 1000MB. But we did not set the type of the partition. We pressed t and pressed Enter to set the partition type.

Now we need to enter the partition number, here we enter 3, and then enter the disk classification number. The partition type of the swap partition is 82 (To display all available partition types, press Press l ), and then press w to save the disk partition table.

swap

Use the mkswap command in the next step to format the swap partition:

$ mkswap /dev/sda3

Then activate the newly created swap partition:

$ swapon /dev/sda3

However, our swap partition will not be automatically mounted after restarting. To mount permanently, we need to add content to the /etc/fstab file. Open the /etc/fstab file and enter the following lines:

$ vi /etc/fstab

/dev/sda3 swap  swap  default  0  0

Save and close the file. Now our swap partition can be used after every reboot.

Second method (use fallocate command)

我推荐用这种方法因为这个是最简单、最快速的创建交换空间的方法了。fallocate 是最被低估和使用最少的命令之一了。 fallocate 命令用于为文件预分配块/大小。

使用 fallocate 创建交换空间，我们首先在 / 目录下创建一个名为 swap_space 的文件。然后分配 2GB 到 swap_space 文件：

$ fallocate -l 2G /swap_space

我们运行下面命令来验证文件大小：

$ ls -lh /swap_space

然后更改文件权限，让 /swap_space 更安全：

$ chmod 600 /swap_space

这样只有 root 可以读写该文件了。我们再来格式化交换分区（LCTT 译注：虽然这个 swap_space 是个文件，但是我们把它当成是分区来挂载）：

$ mkswap /swap_space

然后启用交换空间：

$ swapon -s

每次重启后都要重新挂载磁盘分区。因此为了使之持久化，就像上面一样，我们编辑 /etc/fstab 并输入下面行：

/swap_space swap  swap  sw  0  0 

保存并退出文件。现在我们的交换分区会一直被挂载了。我们重启后可以在终端运行 free -m 来检查交换分区是否生效。

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