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user22611
Asked: 2015-07-31 10:04:32 +0800 CST

swapon has no effect, /proc/swaps remains empty

  • 772

My Ubuntu server has no more than 512 MB of memory. It is not enough for running Node.js + MongoDB.

Hence I decided to add a swap file:

# dd if=/dev/zero of=/root/myswapfile bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 4.69263 s, 229 MB/s
# mkswap /root/myswapfile
Setting up swapspace version 1, size = 1048572 KiB
no label, UUID=3c64da32-d0b4-49e5-92db-fba961b8ae28
# swapon /root/myswapfile

No error message => successful!

The new swap file should now be listed, but it is not:

# swapon -s
Filename                Type        Size    Used    Priority

(empty list)

How can I make it work? What might be the reason for the missing swap?

swap

4 Answers

  1. First, erase your original swapfile:

    sudo rm /myswapfile

    Next, run the following commands one by one:

    sudo fallocate -l 1G /swapfile
sudo chmod 600 /swapfile
ls -lh /swapfile

    The output should be similar to the following:

    -rw------- 1 root root 1.0G Aug  3 18:20 /swapfile

    Now, run the following commands:

    sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon -s

    Now, edit /etc/fstab to make the changes permanent:

    sudo nano /etc/fstab

    and add the following line to the end of the file:

    /swapfile    none            swap    sw              0       0

    Press CTRL + o and then press ENTER to save the file.

    Press CTRL + x to exit nano.

    source: https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04

    If that still doesn't work, you may want to check swappiness:

    cat /proc/sys/vm/swappiness

    This command should return a number. The default should be 60.

    If no output, run the following commands one by one:

    sudo sysctl vm.swappiness=60
echo "vm.swappiness = 60" | tee -a /etc/sysctl.conf

    The -a is important after tee or you will overwrite the entire file!!!

    • 8

  2. You swap file should be in /swapfile with 600 rights.

    #moving file and changing rights
sudo mv /root/myswapfile /myswapfile
sudo chmod 600 /myswapfile

sudo mkswap /myswapfile

    add swap file. I think you forget this command

    sudo swapon /myswapfile
#check swap is working
sudo swapon -s
    • 1

  3. Use fdisk to create a swap. Add a new partition, select Linux swap, write the changes. mkswap /dev/sd? You need to add it to your /etc/fstab/. Change XXX to the swap UUID.

    UUID=XXX none            swap    sw              0       0

    Run swapon -a to make it available from /etc/fstab.

    • 1

  4. you could do this:

    sudo umount -a
gedit /etc/fstab

    and write in where swap is this:

    /proc/swap     proc   default  errors=noremount     1

    and then this:

    sudo mount -a

    and then run gpart and set the swap drive as swap, and mount it on the root dev drive, and it might work fine this way.

    • -1