148

Is there a way to increase my existing "swapfile" without having to destroy and re-create it? I would like to up my swap space from 1GB to 2GB. Currently it is set up as such:

$ sudo swapon -s
Filename                Type        Size    Used    Priority
/swapfile               file        1048572 736640  -1
$ ls -lh /swapfile
-rw------- 1 root root 1.0G Nov  9  2016 /swapfile

I'm using Ubuntu 14.04.

7
  • How much RAM do you have? Is 2G enough? I think that you'll have to swapoff, create a new /swapfile, mkswap, and swapon -a
    – heynnema
    Jun 21, 2017 at 21:16
  • 1
    Add a new swap file, follow the instruction of the above question. you can have 2 swap file ;)
    – Ravexina
    Jun 21, 2017 at 21:16
  • 1
    @Ravexina, A newbie question perhaps, but why would I want to add a new swap file rather than increasing the size of the existing one? Or is it not possible to increase an existing swap file?
    – Dave
    Jun 21, 2017 at 21:25
  • @Dave That's possible too, as you may know we can swapoff then dd and mkswap finally swapon. I thought you don't want to touch your file.
    – Ravexina
    Jun 21, 2017 at 21:29
  • @Ravexina, I don't want to destroy the swapfile. If what your suggesting destroys the swapfile but is the only way, I'm in.
    – Dave
    Jun 21, 2017 at 21:55

6 Answers 6

188

First disable swap file:

sudo swapoff /swapfile

Now let's increase the size of swap file:

sudo dd if=/dev/zero of=/swapfile bs=1M count=1024 oflag=append conv=notrunc

The above command will append 1GiB of zero bytes at the end of your swap file.

Setup the file as a "swap file":

sudo mkswap /swapfile

enable swaping:

sudo swapon /swapfile

On a production system, if your operating system does not let you to disable the swap file using sudo swapoff /swapfile and you receive a messages similar to:

swapoff failed: Cannot allocate memory

Then You might consider having multiple swap files or create a new larger one, initialize it and then remove the old smaller one.

15
  • 9
    sudo fallocate -l 2G /swapfile is probably safer than dd (although it doesn't keep the original swapfile), and it also needs a sudo chmod 600 /swapfile.
    – heynnema
    Jun 21, 2017 at 23:18
  • 21
    @heynnema Doesn't fallocate make sparse files? The swapon manpage says sparse swap files are problematic (specifically mentioning fallocate).
    – muru
    Jun 22, 2017 at 1:37
  • 5
    @heynnema no, the mkswap manpage also says that the files should not contain any holes.
    – muru
    Jun 22, 2017 at 1:46
  • 2
    @muru guess I'm wrong :-) Every time that I read how to create a /swapfile with the onset of 17.04 they used fallocate. I guess that we'll just have to use "disk destroyer"!
    – heynnema
    Jun 22, 2017 at 1:50
  • 1
    @heynnema: What you could do is to use fallocate to pre-allocate disk space and then use dd to fill the holes with zeros. Jun 22, 2017 at 9:49
94

You should add a new swapfile instead of resizing the exist one because it costs you nothing to do so. To resize a swapfile, you must first disable it, which evicts the swap contents to RAM, which increases pressure on RAM and may even summon the OOM killer (not to mention that you could possibly be thrashing your disks for several minutes). Multiple swap files are not a problem, it's trivially easy to setup yet another swap file. There's quite literally no benefit to resizing a swap file over adding another.

dd if=/dev/zero of=/some/file count=1K bs=1M
mkswap /some/file
sudo chown root:root /some/file
sudo chmod 600 /some/file
sudo swapon /some/file
14
  • 3
    And does count=1K give a 1G file? count is in block size, yes? And that can be 512/4096? Or is my math wrong?
    – heynnema
    Jun 22, 2017 at 2:06
  • 6
    +1 This approach also makes it easy to disconnect one of the swapfiles if you later decide you need the disk space back. Jun 22, 2017 at 8:51
  • 4
    This really needs to be marked as the correct answer. Wow, bravo! Apr 27, 2018 at 23:36
  • 4
    «because it costs you nothing to do so» Except for hibernation. «The suspend image cannot span multiple swap partitions and/or swap files. It must fully fit in one swap partition or one swap file.[» wiki.archlinux.org/index.php/Power_management/…
    – tuxayo
    Jan 6, 2020 at 19:23
  • 2
    Actual source: «Q: Does swsusp (to disk) use only one swap partition or can it use multiple swap partitions (aggregate them into one logical space)? A: Only one swap partition, sorry.» kernel.org/doc/Documentation/power/swsusp.txt
    – tuxayo
    Jan 6, 2020 at 19:26
28

You can create another swap file as i did:

  1. sudo fallocate -l 4G /swapfile
  2. sudo chmod 600 /swapfile
  3. sudo mkswap /swapfile
  4. sudo swapon /swapfile
  5. Verify it is working with sudo swapon --show
    To make it permanent add a file to the fstabfile typing:
    echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
6
  • 2
    Please note that fallocateshould bit be used to create the file, as it creates a sparce file. see man mkswap Feb 22, 2019 at 3:13
  • 1
    @CharlesGreen it worked me as i wrote, so it should work for almos anyone.
    – borekon
    Mar 10, 2019 at 17:23
  • 1
    I would sugegst reading man mkswap, especially the last pargraph before "Environment" Mar 10, 2019 at 19:23
  • 1
    worked on NanoPi Neo with Armbian v 5.65
    – user649578
    Apr 14, 2019 at 20:47
  • 1
    As of kernel 5.7 swap files created with fallocate will not always work, and dd is the recommended solution. Ex: "sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 status=progress". See man.archlinux.org/man/swapon.8#Files_with_holes
    – Albin
    Apr 18, 2021 at 2:55
22

(this answer completely rewritten since the downvote)

Notes about fallocate vs dd

Before we continue, I want to point out that some answers use fallocate to allocate space for a file, instead of dd. Don't do that. Use dd. @muru pointed out some important points here and here. Although fallocate is much much faster, it may create files with holes. I think that simply means the space is not contiguous, which is bad for swap files. I picture this as meaning that fallocate creates a C-style linked-list of memory, whereas dd creates a C-array contiguous block of memory. Swap files need a contiguous block. dd does this by doing a byte-for-byte copy of binary zeros from the /dev/zero pseudo-file into a new file it generates.

man swapon also states not to use fallocate, and to use dd instead. Here is the quote (emphasis added):

NOTES

You should not use swapon on a file with holes. This can be seen in the system log as

swapon: swapfile has holes.

The swap file implementation in the kernel expects to be able to write to the file directly, without the assistance of the filesystem. This is a problem on preallocated files (e.g. fallocate(1)) on filesystems like XFS or ext4, and on copy-on-write filesystems like btrfs.

It is recommended to use dd(1) and /dev/zero to avoid holes on XFS and ext4.

And from man mkswap (emphasis added):

Note that a swap file must not contain any holes. Using cp(1) to create the file is not acceptable. Neither is use of fallocate(1) on file systems that support preallocated files, such as XFS or ext4, or on copy-on-write filesystems like btrfs. It is recommended to use dd(1) and /dev/zero in these cases. Please read notes from swapon(8) before adding a swap file to copy-on-write filesystems.

So, use dd, not fallocate, to create the swap files.

Option 1 (my preference): delete the old swap file and create a new one of the correct size:

Rather than resizing the swap file, just delete it and create a new one at the appropriate size!

swapon --show               # see what swap files you have active
sudo swapoff /swapfile      # disable /swapfile
# Create a new 16 GiB swap file in its place (could lock up your computer 
# for a few minutes if using a spinning Hard Disk Drive [HDD], so be patient)
sudo dd if=/dev/zero of=/swapfile count=16 bs=1G
sudo mkswap /swapfile       # turn this new file into swap space
sudo chmod 0600 /swapfile   # only let root read from/write to it, for security
sudo swapon /swapfile       # enable it
swapon --show               # ensure it is now active

In case you are adding this swap file for the first time, ensure it is in your /etc/fstab file to make the swap file available again after each reboot. Just run these two commands:

# Make a backup copy of your /etc/fstab file just in case you
# make any mistakes
sudo cp /etc/fstab /etc/fstab.bak
# Add this swapfile entry to the end of the file to re-enable
# the swap file after each boot
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Source: see the "Step 4: Make the changes permanent" section here.

Option 2: resize the old swap file:

The accepted answer by @Ravexina is correct. However, initially I didn't understand all of its pieces, so I wanted to include some more descriptions and explain more of the details. See dd --help and man dd. Some of my learning on this comes from Bogdan Cornianu's blog post as well. I also add a few commands at the end to show how to verify your swap space once you create it.

How to resize swap file:

Here we will increase the size of the existing swap file by writing 8 GiB (Gibibytes) of zeros to the end of it.

  1. Turn off usage of just this one swap file (located at "/swapfile"):

     # Do this
     sudo swapoff /swapfile
    
     # NOT this, which unnecessarily disables all swap files or partitions
     # sudo swapoff --all
     # or
     # sudo swapoff -a
    
  2. Increase the size of the swap file by 8 GiB by appending all zero bytes to the end of it (rather than rewriting the whole file, which would be slower):

     sudo dd if=/dev/zero of=/swapfile bs=1G count=8 oflag=append conv=notrunc
    
    • if = input file

    • /dev/zero = a special Linux "file" which just outputs all zero bytes every time you read from it

    • of = output file

    • bs = block size

      • Here, 1G stands for 1 Gibibyte, or GiB, which is the base-2 version of "Gigabyte, which is base-10. According to man dd, G =1024*1024*1024 bytes. This is how I like to size files since computers and hardware memory are base-2.
      • If you'd like to use 1 Gigabyte, or GB, which is the base-10 version of "Gibibyte", which is base-2, then you must instead use 1GB rather than 1G. man dd shows that GB =1000*1000*1000 bytes.
    • count = multiplier of blocks; the total memory written will be count * bs.

    • oflag=append means to append to the end of the output file, rather than rewriting the whole thing. See dd --help and man dd. From dd --help:

      append    append mode (makes sense only for output; conv=notrunc suggested)
      
    • conv=notrunc means when "converting" the file, "do not truncate the output file"; dd --help, as you can see just above, shows this is recomended whenever doing oflag=append

    • Note: if you wanted to rewrite the whole swap file rather than just appending to it, you could create a 32 GiB swapfile like this, for example:

        sudo dd if=/dev/zero of=/swapfile bs=1G count=32
      
  3. Make the file usable as swap

     sudo mkswap /swapfile
    
  4. Turn on the swap file

     sudo swapon /swapfile
    
  5. (Bonus/Optional): ensure this swap file you just created is now in usage:

     swapon --show
    

    Sample output:

    $ swapon --show
    NAME      TYPE SIZE USED PRIO
    /swapfile file  64G 1.8G   -2
    

    You can also look at some memory/swap info with these two commands as well:

     # 1. Examine the /proc/meminfo file for entries named "swap", such 
     # as the "SwapTotal" line
     cat /proc/meminfo | grep -B 1000 -A 1000 -i swap
    
     # 2. Look at total memory (RAM) and swap (virtual memory) used
     # and free:
     free -h
    

References:

  1. @Ravexina's answer
  2. Bogdan Cornianu's blog post here: https://bogdancornianu.com/change-swap-size-in-ubuntu/
  3. "How to Create and Use Swap File on Linux": https://itsfoss.com/create-swap-file-linux/

See also:

  1. My answer where I use the above information about increasing your swapfile size in order to solve an out-of-memory Bazel build error: Stack Overflow: java.lang.OutOfMemoryError when running bazel build
7
  • 3
    To the downvoter, I just massively rewrote this answer to make it expound upon and add new information to the knowledge-base already provided in the existing answers. I think it adds value now. Aug 4, 2020 at 1:08
  • I now have two swapfiles, one in /dev/sda2 and /swapfile. Which one will debian catch up for hibernate? With pm-hibernate I get Failed to hibernate system via logind: Access denied Failed to start hibernate.target: Unit hibernate.target is masked. Before the swapfile creation I got Failed to hibernate system via logind: Not enough swap space for hibernation
    – Timo
    Aug 4, 2021 at 20:02
  • 1
    @Timo, any active swap file can be used, I believe. What does swapon --show show? Which of those two swap files is active? If both, the system can decide what to use and how, I assume, using both perhaps simultaneously even, as it sees fit. Aug 4, 2021 at 23:58
  • 1
    This answer should be the best :). thks to you i did this very simple
    – Alex Rivas
    Aug 12, 2021 at 20:24
  • 1
    Solid answer, clear and well documented. May 19 at 19:41
6

I have good results on my Ubuntu 17.04 following the advice of Arian Acosta from the blogpost. One can substitute the 4G here sudo fallocate -l 4G /swapfile with any amount of gigabytes you want. For example sudo fallocate -l 2G /swapfile for TS.

Generally speaking, the recommended size for a swap file is 2X the amount of RAM, but you can make it as big as you need. Remember that this is not a substitute for memory because performance is much worse since things are stored in the disk.

I’ve created a simple bash script that increments the swap file to 4GB and tested it on Ubuntu 16.04.

This can be run line by line or a bash script, but I use it to make headless installations.

#!/bin/bash
echo "====== Current Swap ======"
sudo swapon -s
echo "====== Turning Off Swap ======"
sudo swapoff /swapfile
echo "====== Allocating 4GB Swap ======"
sudo fallocate -l 4G /swapfile
echo "====== Making Swap ======"
sudo mkswap /swapfile
echo "====== Setting Permissions to Root Only  ======"
sudo chmod 600 /swapfile
echo "====== Turning On Swap ======"
sudo swapon /swapfile
echo "====== Current Swap ======"
sudo swapon -s
echo "====== Done! ======"
2
  • 3
    You should have added an argument to the script, which is the amount of SWAP to be added and finally add it to fstab. But still, i like this
    – LnxSlck
    Nov 24, 2018 at 10:48
  • As of kernel 5.7 swap files created with fallocate will not always work, and dd is the recommended solution. Ex: "sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 status=progress". See man.archlinux.org/man/swapon.8#Files_with_holes
    – Albin
    Apr 18, 2021 at 2:54
1

You might also want to check permissions. Other way to do this:

# check your swap
free

# turn off swap
sudo swapoff /swapfile

# To create the SWAP file, you will need to use this.
sudo fallocate -l 4G /swapfile  # same as "sudo dd if=/dev/zero of=/swapfile bs=1G count=4"

# Secure swap.
sudo chown root:root /swapfile
sudo chmod 0600 /swapfile

# Prepare the swap file by creating a Linux swap area.
sudo mkswap /swapfile

# Activate the swap file.
sudo swapon /swapfile

# Confirm that the swap partition exists.
sudo swapon -s

# check your swap again
free
1
  • Answer removes swap, e.g. not what the OP asked.
    – DustWolf
    Jun 21 at 15:28

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