CentOS 7 – Troubleshooting Swap Space Enabling Issues

centosswap

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 /

Best Answer

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 moving ahead with chmod, mkswap & swapon commands. Bingo ! It worked.

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