How to Move Raspbian swapfile to USB

Running your raspberry pi from SDcard works, but has its foibles. For one, consistent reading and writing to and from an SDcard is a sure recipe for failure. Sure, the little memory cards are fast and cheap, but they don’t take well to this kind of abuse. Especially the unrelenting i/o of a swapfile. Better to move your swapfile from the SDcard to a USB device. From Ubuntu 18.04 onwards, a swapfile rather than a dedicated swap partition is used. The swap file is named “swapfile”. First, find the swap file and delete it.

root@pi4:~# swapon -s
Filename Type Size Used Priority
/var/swap file 102396 0 -2
root@pi4:~# cd /var
root@pi4:/var# ls -la
total 102448
drwxr-xr-x 11 root root 4096 Feb 13 11:31 .
drwxr-xr-x 21 root root 4096 Feb 13 11:31 ..
drwxr-xr-x 2 root root 4096 Apr 16 07:56 backups
drwxr-xr-x 15 root root 4096 Apr 15 15:04 cache
drwxr-xr-x 47 root root 4096 Apr 15 15:04 lib
drwxrwsr-x 2 root staff 4096 Feb 8 21:47 local
lrwxrwxrwx 1 root root 9 Feb 13 10:51 lock -> /run/lock
drwxr-xr-x 9 root root 4096 Apr 16 00:01 log
drwxrwsr-x 2 root mail 4096 Feb 13 10:51 mail
drwxr-xr-x 2 root root 4096 Feb 13 10:51 opt
lrwxrwxrwx 1 root root 4 Feb 13 10:51 run -> /run
drwxr-xr-x 5 root root 4096 Feb 13 11:09 spool
-rw------- 1 root root 104857600 Feb 13 11:31 swap   <--- Thar she blows!!!
drwxrwxrwt 4 root root 4096 Apr 16 13:14 tmp
root@pi4:/var# swapoff /var/swap
root@pi4:/var# rm /var/swap

Find your USB drive. Mine is /dev/sda1 that I’ve got mounted as ‘/’. You can move your entire filesystem to USB, by following these directions.

root@pi4:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 1 7.5G 0 disk
└─sda1 8:1 1 7.5G 0 part /
mmcblk0 179:0 0 29.8G 0 disk
├─mmcblk0p1 179:1 0 256M 0 part /boot
└─mmcblk0p2 179:2 0 29.6G 0 part
root@pi4:~#

Create a new swap file of the desired size. I generally use a 4GB swap. Determine the size of your swap file. If you want to make a 4 GB swap file, you will need to write 4 * 1024 blocks of 10242 bytes (= 1 MiB). That will make your count equal to 4 * 1024 = 4096. Create the file of this size with the command:

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096

Assign it read/write permissions for root only (not strictly needed, but it tightens security)

sudo chmod 600 /swapfile

Format the file as swap:

sudo mkswap /swapfile

The file will be activated on the next reboot. If you want to activate it for the current session:

sudo swapon /swapfile

You can check the swap that is available with the command swapon -s (no root permissions needed). And there you have it! You’re swapping to and from USB thumb-drive. Congratulations for not having to worry about blowing out your SDcard!