Swap: Difference between revisions
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== Procedure == | == Procedure == | ||
Here's a procedure that you can run as root, or an administrative user with sudo privileges. | Here's a procedure that you can run as root, or an administrative user with sudo privileges. If you want more info, or want to '''modify''' your swapfile, see [https://askubuntu.com/questions/927854/how-do-i-increase-the-size-of-swapfile-without-removing-it-in-the-terminal the AskUbuntu thread here] | ||
<syntaxhighlight lang="bash"> | <syntaxhighlight lang="bash"> | ||
# see if it's enabled? | # see if it's enabled? | ||
| Line 12: | Line 12: | ||
df -h | df -h | ||
# lets make a swap file that is 2x RAM | # lets make a swap file that is 2x RAM | ||
dd if=/dev/zero of=/swapfile bs=1G count=2 | |||
# fallocate is faster than dd because it doesn't actually write 2GB of zeroes | # fallocate is faster than dd because it doesn't actually write 2GB of zeroes | ||
# however, | # however, as of 2025 it is still best to NOT write sparse files, and therefore use dd | ||
fallocate -l 2G /swapfile | # fallocate -l 2G /swapfile | ||
# set permissions so that nobody but root can read/write | # set permissions so that nobody but root can read/write | ||
chmod 600 /swapfile | chmod 600 /swapfile | ||
Latest revision as of 11:35, 30 October 2025
Swap memory is a file-system based temporary storage for memory to allow a system to shuffle between different tasks that would otherwise consume all available physical memory (RAM). Cloud providers like AWS[1] and Digital Ocean[2] do not setup swap on their default images. So, it's up to you to enable swap. RedHat provides an overview of swap where you can learn the basics of Virtual Memory Management, paging, swapping, and thrashing.
Procedure
Here's a procedure that you can run as root, or an administrative user with sudo privileges. If you want more info, or want to modify your swapfile, see the AskUbuntu thread here
# see if it's enabled?
swapon -s
# check how much RAM we have (also tells you swap is zero)
free -m
# how much disk do we have, and where?
df -h
# lets make a swap file that is 2x RAM
dd if=/dev/zero of=/swapfile bs=1G count=2
# fallocate is faster than dd because it doesn't actually write 2GB of zeroes
# however, as of 2025 it is still best to NOT write sparse files, and therefore use dd
# fallocate -l 2G /swapfile
# set permissions so that nobody but root can read/write
chmod 600 /swapfile
# setup the swap area
mkswap /swapfile
# turn it on
swapon /swapfile
# show it for confirmation
swapon -s
# make it permanent in the file system
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
# there are some other problems with a default Droplet
# swappiness is too high, and cache pressure is too high
cat << HERE | sudo tee -a /etc/sysctl.d/10-swap.conf
# swappiness for a VM should be closer to zero
# 60 might be good for a desktop
# 10 for a server
vm.swappiness=10
# you can check cache_pressure with
# cat /proc/sys/vm/vfs_cache_pressure
# Default is 100 at Digital Ocean which is bad
# set it lower
vm.vfs_cache_pressure=50
HEREFeature
This is the subject of a feature request https://github.com/freephile/meza/issues/176
