How to Enable a Swap File on Linux

There's only 512MB physical memory and no swap on the server:

And we'd like to take advantage of the virtual memory - swap in case the server runs into out of memory. Let's see what swap is used currently:

Nope, there's no swap enabled.

Now, let's begin to create and enable a swap file. Alternatively, you may consider to increase swap partition for your server.

1. Initialize 512MB swap file by dd:
[root@test ~]# dd if=/dev/zero of=/swapfile bs=1024 count=512k
524288+0 records in
524288+0 records out
536870912 bytes (537 MB) copied, 54.5613 s, 9.8 MB/s
2. Make the swap:
[root@test ~]# mkswap /swapfile
mkswap: /swapfile: warning: don't erase bootbits sectors
        on whole disk. Use -f to force.
Setting up swapspace version 1, size = 524284 KiB
no label, UUID=ccb357c3-b325-468d-8db2-6a4e3bdfde93

3. Enable the swap file:
[root@test ~]# swapon /swapfile
[root@test ~]# swapon -s
Filename                                Type            Size    Used    Priority
/swapfile                               file            524280  0       -1
4. Persist the setting to /etc/fstab:
[root@test ~]# vi /etc/fstab
...
/swapfile               swap                    swap    defaults        0 0
...


5. Change the default permission into private:
[root@test ~]# ls -l /swapfile
-rw-r--r--. 1 root root 536870912 Apr 15 11:55 /swapfile
[root@test ~]# chmod 600 /swapfile
[root@test ~]# ls -l /swapfile
-rw-------. 1 root root 536870912 Apr 15 11:55 /swapfile


Now, we have swap enabled on the server:

We made it.