选题: Creating SWAP partition using FDISK & FALLOCATE commands

sources/tech/20170802 Creating SWAP partition using FDISK & FALLOCATE commands.md

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+translating by lujun9972
+Creating SWAP partition using FDISK & FALLOCATE commands
+======
+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.
+
+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.
+
+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
+
+  *  **Using fdisk command**
+  *  **Using fallocate command**
+
+
+
+###  First Method (Using Fdisk command)
+
+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.
+
+Firstly we will create a partition,
+
+```
+$ fdisk /dev/sda
+```
+
+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.
+
+![swap][2]
+
+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.
+
+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.
+
+![swap][4]
+
+Next we will format our swap partition  using mkswap command
+
+```
+$ mkswap /dev/sda3
+```
+
+& will then activate our newly created swap
+
+```
+$ swapon /dev/sda3
+```
+
+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
+
+```
+$ vi /etc/fstab
+```
+
+```
+/dev/sda3 swap  swap  default  0  0
+```
+
+Save & close the file. Our swap now will even work after a reboot.
+
+### Second Method (using fallocate command)
+
+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.
+
+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 ,
+
+```
+$ fallocate -l 2G /swap_space
+```
+
+We will then verify the size of the file by running
+
+```
+ls-lh /swap_space.
+```
+
+Next, we will make our /swap_space more secure by changing the file permissions
+
+```
+$ chmod 600 /swap_space**
+```
+
+Now only root will be able to read, write on this file. We will now format the swap partition,
+
+```
+$ mkswap /swap_space
+```
+
+& then will turn on our swap
+
+```
+$ swapon -s
+```
+
+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
+
+```
+/swap_space swap  swap  sw  0  0 
+```
+
+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.
+
+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.
+
+
+--------------------------------------------------------------------------------
+
+via: http://linuxtechlab.com/create-swap-using-fdisk-fallocate/
+
+作者：[Shusain][a]
+译者：[lujun9972](https://github.com/lujun9972)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]:http://linuxtechlab.com/author/shsuain/
+[1]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=668%2C211
+[2]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk.jpg?resize=668%2C211
+[3]:https://i1.wp.com/linuxtechlab.com/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif?resize=620%2C157
+[4]:https://i0.wp.com/linuxtechlab.com/wp-content/uploads/2017/02/fidsk-swap-select.jpg?resize=620%2C157