Ubuntu 18.04 开启 swapfile

Ubuntu 18.04 开启 swapfile

开启 swapfile 的动机在于，本机唤醒时间太慢，尝试解决这个问题。
本机已经 锁屏休眠时间 设置为 Never，但是唤醒还得5-6秒。怀疑是不是本机适用的是硬盘休眠，所以唤醒慢；理想的状态是内存睡眠，唤醒更快一些。

注意区分两个概念

• 睡眠 Suspend to RAM，简称 STR，比如 Intel 的 modern standby
• 休眠 Suspend to Disk，简称 STD

吐槽一句，休眠这个名字太迷惑了，和睡眠根本分不清，不如叫“冬眠”更合适。

查看 /sys/power/state 得到：

freeze mem disk

可以看出，本机其实是支持 STR 和 STD 两种节能模式的。

但是我没找到怎么设置使用 STR 的地方，那就先看看 STD 怎么搞快一点吧。毕竟，明明用的固态硬盘，唤醒还得好几秒，太不像话。

本机有32G内存，查看swap，sudo swapon --show 得到：

NAME      TYPE      SIZE USED PRIO
/dev/sda3 partition 977M 7.3M   -2

可以看到是使用的交换分区，并且分区远小于内存大小。这可能会对休眠功能造成影响，我们接下来将它扩大到和内存一样大。
使用 swapfile 相比于 swap partition 的好处是，关闭交换之后，可以像普通文件一样直接 rm 删除。

参考 Linuxize的这篇博客，我们来新增一个32G的交换文件。

以下是全文转载。

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How to Add Swap Space on Ubuntu 18.04

Updated Feb 6, 2020

Swap is a space on a disk that is used when the amount of physical RAM memory is full. When a Linux system runs out of RAM, inactive pages are moved from the RAM to the swap space.

Swap space can take the form of either a dedicated swap partition or a swap file. Generally when running Ubuntu on a virtual machine, a swap partition is not present, and the only option is to create a swap file.

This tutorial covers the steps necessary to add a swap file on Ubuntu 18.04 systems.

Before You Begin

Before continuing with this tutorial, check if your Ubuntu installation already has swap enabled by typing:

$ sudo swapon --show

If the output is empty, it means that your system does not have swap space enabled.
Otherwise, if you get something like below, you already have swap enabled on your machine.

NAME      TYPE      SIZE USED PRIO
/dev/sda2 partition 1.9G   0B   -2

Although possible, it is not common to have multiple swap spaces on a single machine.

Creating a Swap File

The user you are logged in as must have sudo privileges to be able to activate swap. In this example, we will add 1G swap. If you want to add more swap, replace 1G with the size of the swap space you need.

Perform the steps below to add swap space on Ubuntu 18.04.

1. Start by creating a file which will be used for swap:

$ sudo fallocate -l 1G /swapfile

If fallocate is not installed or you get an error message saying fallocate failed: Operation not supported then use the following command to create the swap file:

$ sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576

2. Only the root user should be able to write and read the swap file. Set the correct permissions by typing:

$ sudo chmod 600 /swapfile

3. Use the mkswap utility to set up a Linux swap area on the file:

$ sudo mkswap /swapfile

4. Activate the swap file using the following command:

$ sudo swapon /swapfile

To make the change permanent open the /etc/fstab file:

$ sudo nano /etc/fstab

and paste the following line:

/swapfile swap swap defaults 0 0

5. Verify that the swap is active by using either the swapon or the free command , as shown below:

$ sudo swapon --show
NAME      TYPE  SIZE   USED PRIO
/swapfile file 1024M 507.4M   -1

$ sudo free -h
              total        used        free      shared  buff/cache   available
Mem:           488M        158M         83M        2.3M        246M        217M
Swap:          1.0G        506M        517M

Adjusting the Swappiness Value

Swappiness is a Linux kernel property that defines how often the system will use the swap space. Swappiness can have a value between 0 and 100. A low value will make the kernel to try to avoid swapping whenever possible, while a higher value will make the kernel to use the swap space more aggressively.

The default swappiness value is 60. You can check the current swappiness value by typing the following command:

$ cat /proc/sys/vm/swappiness
60

While the swappiness value of 60 is OK for most Linux systems, for production servers, you may need to set a lower value.
For example, to set the swappiness value to 10, run:

$ sudo sysctl vm.swappiness=10

To make this parameter persistent across reboots, append the following line to the /etc/sysctl.conf file:

vm.swappiness=10

The optimal swappiness value depends on your system workload and how the memory is being used. You should adjust this parameter in small increments to find an optimal value.

Removing a Swap File

To deactivate and remove the swap file, follow these steps:

1. Start by deactivating the swap space by typing:

$ sudo swapoff -v /swapfile

2. Next, remove the swap file entry /swapfile swap swap defaults 0 0 from the /etc/fstab file.
3. Finally, remove the actual swapfile file using the rm command:

$ sudo rm /swapfile

Conclusion

You have learned how to create a swap file and activate and configure swap space on your Ubuntu 18.04 system.

If you hit a problem or have feedback, leave a comment below.