Howto Extra Swap without having to repartition

June 19, 2010 by rich scadding Leave a Comment

This is a great little trick if for some reason you need a little extra Swap. You may face a situation where your RAM and Swap are being eaten up by a hungry app. Well, no problem, all though not as fast or efficient as extra RAM or a bigger Swap partition, it is still handy in some situations.

How to add more Linux Swap with Swap File

Assuming you want to put it in “/”, Create an empty 500MB file
$ sudo dd if=/dev/zero of=/swap.img bs=1024k count=512

Format it as a swap file
$ sudo mkswap /swap.img

Add it to your running Linux system
$ sudo swapon /swap.img

Optionally you can add /swap.img to fstab for automatic swap activation.

$ sudo nano /etc/fstab

Add this line at the end of the file
/swap.img none swap sw 0 0

Then Ctrl+X, Y to save and Enter to close Nano

Run “free -m” command to verify that you’ve added the newly created swap to your Linux based operating system.

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Ubuntu Slowdown – Dual Boot Loses Swap UUID [Fix]

December 16, 2009 by rich scadding 3 Comments

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ubuntu-logo-100x90This was reported as an issue before when dual-booting Ubuntu with another distro. Basically the Swap UUID Doesn’t get updated in /etc/fstab when another distro is installed on another partition.

I installed Fedora for a test run on a spare partition, with Grub being installed to MBR.

Later after an Ubuntu update, which included a new kernel and also a newer Grub, Ubuntu took back control of Grub.

I booted into Ubuntu, only to find that everything was a bit sluggish, and having experienced this before, I checked my Swap partition in  readiness to solve this problem which I had a feeling was repeating itself.

Check Swap:

free -m

With the result:

Swap:            0          0          0

Fix with “blkid” to find the real UUID of the Swap Partition:

blkid


/dev/sda1: LABEL="ACER" UUID="320D-180E" TYPE="vfat"
/dev/sda2: LABEL="Fedora-12-i686-L" UUID="3b915b51-c7ce-4077-975d-df2a177b94cb" TYPE="ext4"
/dev/sda3: UUID="78a42ee0-4d8a-474c-9cd6-b3f3a6dd6449" TYPE="ext4"
/dev/sda4: UUID="4bfbb29b-78da-4172-ae54-b1bb934de7f5" TYPE="swap"

Then use Nano to Fstab and change the old Swap UUID to the new UUID:

sudo nano /etc/fstab

Now just turn Swap on and check used memory again:

sudo swapon -a

with the result:

free -m

   Swap:         1153          0       1153

So there you have it, if you install another Linux distro on a spare partition to dual-boot and use the same Swap partition, you may find that when you boot into Ubuntu that it is a little sluggish than usual.

This is a known problem for dual and triple booters, but easily remedied, as you see above.

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