Recently, I was trying to deploy a WordPress website on a linux server with no PHP and MySQL pre-installed. Installing packages is easy in Linux but things did not go well in my server which only has RAM for 1 GB.
It kept running out of RAM when installing PHP. The server do have 40 GB disk memory but no swap space had been defined.
As it is the first time I did it so I figured that it would useful to note down something for futural references.
What is swap?
- Swapping was the main method of memory management in the 1960s, and was one of several methods commonly used until the 1990s.
- In a multiprogramming system, the total size of all processes may exceed the size of main memory. The memory images of some processes may have to be kept on disk. The parts of the disk(s) used for this are called swap space.
- The kernel could swap out a process, i.e. copy all its memory to swap space, to free up some memory. It would do this to allow another process to be swapped in, i.e. have its image brought into memory from swap space.
Swap in Linux
Following steps are what I did for configuring swap in Linux.
1. Create swap space of 2 GB
[~]# dd if=/dev/zero of=/var/swap bs=1024 count=2048000 2048000+0 records in 2048000+0 records out 2097152000 bytes (2.1 GB) copied, 18.7808 s, 112 MB/s
2. Create swap file
[~]# mkswap /var/swap Setting up swapspace version 1, size = 2047996 KiB no label, UUID=5039b019-2db5-41b2-a289-3caf4fdd98bf [~]#
3. Loading the swap file
[~]# swapon /var/swap swapon: /var/swap: insecure permissions 0644, 0600 suggested. swapon: /var/swap: swapon failed: Device or resource busy [~]#
Well, it asked me to change the file permissions so let’s do that as well.
[~]# chmod 0600 /var/swap [~]#
[~]# swapon /var/swap [~]#
swapon, you should have the swap space configured.
Let’s check if it has been successful.
4. Check free memory
[~]# free -m total used free shared buff/cache available Mem: 991 757 73 0 159 75 Swap: 1999 0 1999 [~]#
Mem denotes the total usable memory for the system.
Swap is the defined swap space in the system. In my case, I configure the
tatal swap space as 2 GB approx.
5. Clear the swap space
If you no longer need it, you can clear it as following:
[~]# swapoff /var/swap [~]#