How to create swap file on ext4

Question

My friend whats to create a 4GB swap file on his ext4 file system. because he is using a chromebook acer c7 the way he installed he did not have a chance to specify swap partition

and now he want to create a swap file on his file system.

This is the guide he is following

http://ubuntuforums.org/showthread.php?t=1618220&p=10098565#post10098565

First you have to create a 2GiB file, for example in /mnt:

sudo dd if=/dev/zero of=/mnt/swap bs=1M count=2048

Then format the file to swap:

sudo mkswap /mnt/swap

Add the swap file to the system:

sudo swapon /mnt/swap

Check it out, i.e.:

free -m

Edit the fstab file:

gksu gedit /etc/fstab

and add this line at the end of the file:

/mnt/swap  none  swap  sw

Save the file and exit. That's all.

This is what he is getting

user@chrubuntu:~$ sudo swapon /mnt/swap
swapon: /mnt/swap: swapon failed: Invalid argument

and his fstab looks like this

any way to fix this ??

One more thing he is using ubuntu 14.04 and it is not a fresh install

Thank you for your time

Solution

It's possible the problem is because it's in the /mnt directory or it could be a security issue world readable swap isn't great. Try this tutorial and see if you have better results.

http://www.cyberciti.biz/faq/linux-add-a-swap-file-howto/

Comments

[jkt123]

Does he get the error you've mentioned both times he tries to run swapon, or just after he's added it to the fstab file?

[Levan]

Thank you for the reply he follows the above guide that i mantioned before this step every thing works Add the swap file to the system: sudo swapon /mnt/swap imgur.com/rFP0gbc

[Levan]

@psusi Thank you for the reply again this is what it say ser@chrubuntu:~$ uname -a Linux chrubuntu 3.4.0 #1 SMP Fri Apr 11 19:07:10 PDT 2014 x86_64 x86_64 x86_64 GNU/Linux user@chrubuntu:~$

[Levan]

@psusi I have a question, what do you think if he manually upgrades to the latest kernel?? will his chrome book still boot or it is too dangerous

[psusi]

I don't know enough about it, but it certainly appears to have a custom, older, kernel, but if you check its config file in /boot, you may find that it was built without CONFIG_SWAP, so doesn't support swap.

[Levan]

@psusi thank you you have been tremendous help, crazy thing is that he can not even upgrade to a newer kernel

[Levan]

Thank you for the reply I will tell him and notify you about the result

[Levan]

Small preamble this is the UUID=c8a5817e-90d3-48f3-976a-8e80de5e6a4b he got this is the command he used sudo swapon -U c8a5817e-90d3-48f3-976a-8e80de5e6a4b and sadly this is what terminal told him swapon cannot find the device

[Levan]

sorry @Elder Geek small mix up this is what he got user@chrubuntu:~$ ls -a /mnt . .. swap user@chrubuntu:~$ I do not understand did not the terminal say that it created a file ??

[psusi]

That's definitely not going to work; uuid recognition only works on partitions, not files.

[Levan]

@psusi any suggestions ??? and thank you fore the reply

[Elder Geek]

@Levan just double-checking