Add a swap partition file in linux and a swap partition in linux

Add a swap partition file in linux and a swap partition in linux

To add a swap partition file in inux, follow these steps:

1. Check the current swap (use free-h, cat/proc/swaps or swapon-s ):

[root@compute ~]# free -h              total        used        free      shared  buff/cache   availableMem:           1.8G        329M        1.2G        8.3M        242M        1.3GSwap:          511M          0B        511M

 

2. View hard disk usage (df-hal ):

[root@compute ~]# df -lhFilesystem               Size  Used Avail Use% Mounted on/dev/mapper/centos-root   15G  2.4G   13G  16% /devtmpfs                 909M     0  909M   0% /devtmpfs                    920M     0  920M   0% /dev/shmtmpfs                    920M  8.4M  912M   1% /runtmpfs                    920M     0  920M   0% /sys/fs/cgroup/dev/mapper/centos-home   55G   33M   55G   1% /home/dev/sda1                797M  180M  618M  23% /boottmpfs                    184M     0  184M   0% /run/user/0

 

3. Run the dd command to create a swap file named swapfile (the file name and directory are arbitrary ):

dd  if=/dev/zero  of=/var/swapfile  bs=1024  count=2048k

　　

Popular Science: if (input file, input file), of (output file ). Dev/zero is a special character device (input device) in Linux. It can be used to create an empty file with a specified length for initialization. For example, if a temporary file is exchanged, the device provides 0 infinitely, you can provide any number you need. Bs = 1024: the size of each block that is read/output at the same time is 1024 bytes, that is, 1 kb, and bs (that is, block size ). Count = 2048000: the number of data blocks is 2048000, that is, 2048000 1 kb. The size of swap partition can be calculated as: 1KB * 2097152 = 1KB * 1024 (k) * 1024*2 = 2097152 = 2G. (The unit M in the dd command indicates 1024*1024, and k indicates 1024 ).

After you press enter, a 2 GB read/write operation will be executed, and the system will be stuck for a while and wait patiently for the execution result.

After execution, format the swap file and convert it to a swap partition:

mkswap  /var/swapfile

 

4. Mount and activate the partition:

swapon   /var/swapfile

 

5. Run the free-h or swapon-s command to check whether the new swap partition is added and activated.

Modify the fstab configuration and set to automatically mount the partition at startup:

vim    /etc/fstab

/swapfile               swap                    swap    defaults        0 0

 

Reference: http://blog.csdn.net/ausboyue/article/details/73433990