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translate '20170802 Creating SWAP partition using FDISK - FALLOCATE commands.md' done at 2017年 12月 24日 星期日 22:30:17 CST
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translating by lujun9972
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Creating SWAP partition using FDISK & FALLOCATE commands
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======
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Swap-partition holds the memory which is used in case the physical memory (RAM) is full . When RAM capacity has been utilized to maximum , Linux machine moves inactive pages from memory to swap-space which are then used by the system. Though it gets the work done, it should not be considered as a replacement to physical memory/RAM.
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In most cases, it is advised to keep SWAP-memory equal to size of physical memory at minimum & double the size of physical memory at maximum. So if you have 8 GB RAM on your system, Swap should be between 8-16 GB.
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If a swap-partition has not been configured in your Linux system, your system might start killing off the running process/applications & might cause your system to crash. In this tutorial, we will learn to add swap-partition to Linux system & we will be discussing two methods for creating a swap-partition
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* **Using fdisk command**
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* **Using fallocate command**
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### First Method (Using Fdisk command)
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Normally, first hdd of the system is named **/dev/sda** & partitions for it are named **/dev/sda1** , **/dev/sda2**. For this tutorial we will using a HDD that have 2 primary partitions on system i.e. /dev/sda1, /dev/sda2 & SWAP will be /dev/sda3.
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Firstly we will create a partition,
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```
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$ fdisk /dev/sda
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```
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to create a new partition type **' n'** . You will now be asked to enter the first cylinder value, just hit enter key to use default value & then you will asked to enter last cylinder value, here we will enter the size of swap partition (we will be using 1000MB). Enter the value in last cylinder as +1000M.
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![swap][2]
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We have now created a partition of size 1000MB but we have not assigned it any partition type, so to assign a partition type, press **" t"** & press enter.
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Now you will be first asked to enter partition number, which is **3** for our partition & then we will asked to enter partition id which for swap it's **82** (to see list of all available partition types, press **" l"** ) & then press " **w "** to save the partition table.
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![swap][4]
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Next we will format our swap partition using mkswap command
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```
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$ mkswap /dev/sda3
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```
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& will then activate our newly created swap
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```
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$ swapon /dev/sda3
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```
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But our swap will not be mounted automatically after every reboot. To mount it permanently in our system, we need to append /etc/fstab file. Open /etc/fstab file & make an entry of the following line
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```
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$ vi /etc/fstab
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```
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```
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/dev/sda3 swap swap default 0 0
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```
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Save & close the file. Our swap now will even work after a reboot.
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### Second Method (using fallocate command)
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I prefer this method as this is easiest & fastest way to create swap. Fallocate is one of the most underestimated & very less used command. Fallocate is used to pre-allocate blocks/size to a files.
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To create a swap using fallocate, we will firstly create a file named **swap_space** in ** '/'**. Next we will allocate 2GB to our file swap_space ,
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```
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$ fallocate -l 2G /swap_space
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```
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We will then verify the size of the file by running
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```
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ls-lh /swap_space.
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```
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Next, we will make our /swap_space more secure by changing the file permissions
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```
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$ chmod 600 /swap_space**
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```
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Now only root will be able to read, write on this file. We will now format the swap partition,
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```
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$ mkswap /swap_space
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```
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& then will turn on our swap
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```
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$ swapon -s
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```
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This swap partition will need to be remounted after every reboot. So to make it permanent, edit the /etc/fstab, as we did above & enter the following line
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```
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/swap_space swap swap sw 0 0
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```
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Save & exit the file. Our swap will now be permanently mounted. We can check if your swap is working or not by running " **free -m** " on your terminal after rebooting the system.
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This completes our tutorial, I hope it was simple enough to understand & learn. If you are having any issues or have have any queries, please mention them in the comment box below.
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--------------------------------------------------------------------------------
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via: http://linuxtechlab.com/create-swap-using-fdisk-fallocate/
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作者：[Shusain][a]
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译者：[lujun9972](https://github.com/lujun9972)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://linuxtechlab.com/author/shsuain/
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[1]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=668%2C211
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[2]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk.jpg?resize=668%2C211
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[3]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=620%2C157
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[4]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk-swap-select.jpg?resize=620%2C157
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@ -0,0 +1,117 @@
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使用 FDISK 和 FALLOCATE 命令创建交换分区
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======
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交换分区在物理内存(RAM)被填满时用来保持内存中的内容. 当 RAM 被耗尽, Linux 会将内存中不活动的页移动到交换空间中，从而空出内存给系统使用. 虽然如此, 但交换空间不应被认为是可以用来替代物理内存/RAM的.
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大多数情况下, 建议交换内存的大小为物理内存的1到2倍. 也就是说如果你有8GB内存, 那么交换空间大小应该介于8-16 GB.
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若系统中没有配置交换分区, 当内存耗尽后，系统可能会杀掉正在运行中哦该的进程/应哟该从而导致系统崩溃. 在本文中, 我们将学会如何为Linux系统添加交换分区,我们有两个办法:
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+ **使用 fdisk 命令**
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+ **使用 fallocate 命令**
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### 第一个方法(使用 Fdisk 命令)
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通常, 系统的第一块硬盘会被命名为 **/dev/sda** 而其中的分区会命名为 **/dev/sda1** , **/dev/sda2**. 本文我们使用的石块有两个主分区的硬盘,两个分区分别为 /dev/sda1, /dev/sda2，而我们使用 /dev/sda3 来做交换分区.
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首先创建一个新分区,
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```
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$ fdisk /dev/sda
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```
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按 **' n'** 来创建新分区. 系统会询问你从哪个柱面开始, 直接按回车键使用默认值即可。然后系统询问你到哪个柱面结束, 这里我们输入交换分区的大小(比如1000MB). 这里我们输入 +1000M.
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![swap][2]
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现在我们创建了一个大小为 1000MB 的磁盘了。但是我们并没有设个分区的类型, 我们按下 **" t"** 然后回车来设置分区类型.
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现在我们要输入分区编号, 这里我们输入 **3**,然后输入磁盘分类id，交换分区的磁盘类型为 **82** (要显示所有可用的磁盘类型, 按下 **" l"** ) 然后再按下 " **w "** 保存磁盘分区表.
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![swap][4]
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再下一步使用 `mkswap` 命令来格式化交换分区
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```
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$ mkswap /dev/sda3
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```
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然后激活新建的交换分区
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```
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$ swapon /dev/sda3
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```
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然而我们的交换分区在重启后并不会自动挂载. 要做到永久挂载,我们需要添加内容道 `/etc/fstab` 文件中. 打开 `/etc/fstab` 文件并输入下面行
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```
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$ vi /etc/fstab
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```
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```
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/dev/sda3 swap swap default 0 0
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```
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保存并关闭文件. 现在每次重启后都能使用我们的交换分区了.
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### 第二种方法(使用 fallocate 命令)
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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 用于为文件预分配块/大小.
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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道 swap_space 文件,
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```
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$ fallocate -l 2G /swap_space
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```
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我们运行下面命令来验证文件大小
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```
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ls-lh /swap_space.
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```
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然后更改文件权限，让 `/swap_space` 更安全
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```
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$ chmod 600 /swap_space**
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```
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这样只有 root 可以读写该文件了. 我们再来格式化交换分区(译者注：虽然这个swap_space应该是文件，但是我们把它当成是分区来挂载),
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```
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$ mkswap /swap_space
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```
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然后启用交换空间
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```
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$ swapon -s
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```
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每次重启后都要重现挂载磁盘分区. 因此为了使之持久话，就像上面一样，我们编辑 `/etc/fstab` 并输入下面行
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```
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/swap_space swap swap sw 0 0
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```
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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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我们的教程至此就结束了, 希望本文足够容易理解和学习. 如果有任何疑问欢迎提出.
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--------------------------------------------------------------------------------
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via: http://linuxtechlab.com/create-swap-using-fdisk-fallocate/
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作者：[Shusain][a]
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译者：[lujun9972](https://github.com/lujun9972)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://linuxtechlab.com/author/shsuain/
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[1]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=668%2C211
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[2]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk.jpg?resize=668%2C211
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[3]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=620%2C157
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[4]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk-swap-select.jpg?resize=620%2C157
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