mjhjmtu

So I'm following a tutorial to install OTRS which is Open source Ticket Request System. So in order to install, it requires: 4GB of Swap space. Here's the command I used:

[root@ip-10-0-7-41 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 50G 14G 37G 27% /
devtmpfs 478M 0 478M 0% /dev
tmpfs 496M 0 496M 0% /dev/shm
tmpfs 496M 13M 484M 3% /run
tmpfs 496M 0 496M 0% /sys/fs/cgroup
tmpfs 100M 0 100M 0% /run/user/1000
[root@ip-10-0-7-41 ~]# fallocate -l 4G /myswap
[root@ip-10-0-7-41 ~]# ls -lh /myswap
-rw-r--r--. 1 root root 4.0G Jul 8 08:44 /myswap
[root@ip-10-0-7-41 ~]# chmod 600 /myswap
[root@ip-10-0-7-41 ~]# mkswap /myswap
Setting up swapspace version 1, size = 4194300 KiB
no label, UUID=3656082a-148d-4604-96fb-5b4604fa5b2e
[root@ip-10-0-7-41 ~]# swapon /myswap
swapon: /myswap: swapon failed: Invalid argument

You can see : Invalid argument error here. I tried many time in vain to enable it.Someone please tell me how to fix this error.
(I'm running this CentOS 7 on AWS Instance EC2)

[root@ip-10-0-7-41 ~]# df -T | awk 'print $1,$2,$NF' | grep "^/dev"
/dev/xvda1 xfs /

The problem with fallocate(1) is that it uses filesystem ioctls to make the allocation fast and effective, the disadvantage is that it does not physically allocate the space but swapon(2) syscall requires a real space.
Reference : https://bugzilla.redhat.com/show_bug.cgi?id=1129205

I'd faced this issue earlier with my box too. So instead of using fallocate, I used dd as the link suggests

sudo dd if=/dev/zero of=/myswap count=4096 bs=1MiB

and proceeding with chmod, mkswap & swapon commands. Bingo ! It worked.

Follow these steps, it works on DigitalOcean's droplets. I tested. Change the amount 4096 according to your need

yum install nano -y

sudo dd if=/dev/zero of=/swapfile count=4096 bs=1MiB
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

sudo nano /etc/fstab

add this line:

/swapfile swap swap sw 0 0

run this command

sudo sysctl vm.swappiness=10

sudo nano /etc/sysctl.conf

add this line

vm.swappiness = 10
vm.vfs_cache_pressure = 50

To verify swap's size

swapon --summary
free -h