Benjamin L. Stewart

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tagslinux, linux_mint
notes

5 min read

Linux Mint: Preserve Open Apps and Workspaces Across Power Cycles

Purpose

This guide explains how to configure Linux Mint Cinnamon so that open applications, windows, and workspaces can survive a complete power-off/power-on cycle.

The reliable method is hibernation, not a normal reboot.

With hibernation:

  • RAM is written to swap.
  • The computer powers completely off.
  • On the next power-on, Linux restores the saved RAM image.
  • Cinnamon returns with the same applications, windows, and workspaces.

A normal reboot starts a new kernel and user session, so it cannot preserve arbitrary running processes in exactly the same state.

Important Scope and Safety Notes

This guide is intended primarily for:

  • Linux Mint 22.x
  • Cinnamon desktop
  • an ext4 root filesystem
  • a swapfile located at /swapfile
  • systems booting with GRUB

Do not blindly copy commands from this guide onto a system using:

  • Btrfs root
  • LUKS/full-disk encryption with a custom resume setup
  • LVM swap
  • a dedicated swap partition
  • another bootloader
  • another Linux distribution

Those configurations may require different hibernation procedures.

Before making changes:

  1. Save all open work.
  2. Make sure you have a current backup of important files.
  3. Confirm your current swap and filesystem layout.
  4. Do not reuse UUIDs or resume offsets copied from another computer.

Every machine must use its own filesystem UUID and swapfile resume offset.

1. Inspect the System

Start by collecting system information.

echo "===== HOST ====="
hostname

echo
echo "===== MEMORY ====="
free -h

echo
echo "===== ACTIVE SWAP ====="
swapon --show

echo
echo "===== ROOT FILESYSTEM ====="
findmnt /

echo
echo "===== BLOCK DEVICES ====="
lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINTS

echo
echo "===== FREE SPACE ====="
df -h /

echo
echo "===== SECURE BOOT ====="
mokutil --sb-state 2>/dev/null || true

Check the results carefully.

For this guide, you ideally want something resembling:

/dev/nvme0n1p2  ext4  /

You also need enough free SSD space for a hibernation-capable swapfile.

If the root filesystem is Btrfs, stop here and use a Btrfs-specific hibernation procedure instead.

2. Determine the Required Swap Size

Check installed RAM:

free -h

Check current swap:

swapon --show

For hibernation, swap should generally be at least large enough to hold the hibernation image.

A practical guideline is:

Installed RAMSuggested swap
8 GiB16 GiB
16 GiB24 GiB
32 GiB40 GiB
64 GiB72–80 GiB

The exact image size may be smaller than installed RAM because some pages are excluded or compressed, but allocating additional margin makes configuration more reliable.

3. Replace an Undersized /swapfile

Warning

Only perform this section if:

  • swapon --show confirms that /swapfile is your current swap;
  • your root filesystem is ext4;
  • you have enough free RAM to temporarily disable swap;
  • you have enough free disk space;
  • you understand that these commands delete and recreate /swapfile.

Do not run:

sudo rm -f /swapfile

unless you have verified that /swapfile is actually the swapfile you intend to replace.

Example: Create a 40 GiB Swapfile

A 40 GiB swapfile is a reasonable example for a system with approximately 32 GiB RAM.

Disable the existing swapfile:

sudo swapoff /swapfile

Remove it:

sudo rm -f /swapfile

Create the new file:

sudo touch /swapfile
sudo chmod 600 /swapfile

Allocate 40 GiB:

sudo dd if=/dev/zero \
  of=/swapfile \
  bs=1M \
  count=40960 \
  status=progress

Format it as swap:

sudo mkswap /swapfile

Enable it:

sudo swapon /swapfile

Verify:

swapon --show
free -h

You should see something similar to:

NAME      TYPE SIZE USED PRIO
/swapfile file  40G   0B   -1

Check /etc/fstab:

grep -n swap /etc/fstab

A typical entry is:

/swapfile none swap sw 0 0

If /swapfile is not already listed in /etc/fstab, add the appropriate entry before relying on it after reboot.

4. Determine the Root Device and UUID

Run:

ROOT_DEV=$(findmnt -no SOURCE /)
ROOT_UUID=$(blkid -s UUID -o value "$ROOT_DEV")

echo "Root device: $ROOT_DEV"
echo "Root UUID:   $ROOT_UUID"

Example output:

Root device: /dev/nvme0n1p2
Root UUID:   <YOUR_ROOT_UUID>

Do not publish or copy a UUID from another computer into your configuration.

5. Calculate the Swapfile Resume Offset

Linux needs to know where the swapfile physically begins on the filesystem.

Inspect it first:

sudo filefrag -v /swapfile | head -n 10

You may see something similar to:

ext: logical_offset: physical_offset: length: expected: flags:
0:   0..2047:        123456789..123458836: 2048:

The first physical block is not necessarily the final kernel resume offset if filesystem and memory page sizes differ.

Use this calculation instead:

OFFSET_BLOCK=$(sudo filefrag -v /swapfile | \
  awk '$1=="0:" {
      x=$4
      sub(/\.\..*/, "", x)
      print x
      exit
  }')

BLOCK_SIZE=$(sudo tune2fs -l "$ROOT_DEV" 2>/dev/null | \
  awk -F: '/Block size:/ {
      gsub(/[[:space:]]/,"",$2)
      print $2
  }')

PAGE_SIZE=$(getconf PAGESIZE)

RESUME_OFFSET=$(( OFFSET_BLOCK * BLOCK_SIZE / PAGE_SIZE ))

echo
echo "===== HIBERNATION VALUES ====="
echo "Root device:           $ROOT_DEV"
echo "Root UUID:             $ROOT_UUID"
echo "Filesystem block size: $BLOCK_SIZE"
echo "Memory page size:      $PAGE_SIZE"
echo "Resume offset:         $RESUME_OFFSET"

Record:

Root UUID:     <YOUR_ROOT_UUID>
Resume offset: <YOUR_RESUME_OFFSET>

These values are specific to the current system.

6. Configure Initramfs Resume

Create or replace:

/etc/initramfs-tools/conf.d/resume

using the values calculated above:

echo "RESUME=UUID=$ROOT_UUID resume_offset=$RESUME_OFFSET" | \
sudo tee /etc/initramfs-tools/conf.d/resume

Verify:

cat /etc/initramfs-tools/conf.d/resume

It should resemble:

RESUME=UUID=<YOUR_ROOT_UUID> resume_offset=<YOUR_RESUME_OFFSET>

7. Add the Resume Parameters to GRUB

Create a dedicated GRUB fragment:

sudo mkdir -p /etc/default/grub.d

Then:

sudo tee /etc/default/grub.d/99-hibernate.cfg >/dev/null <<EOF
GRUB_CMDLINE_LINUX_DEFAULT="\${GRUB_CMDLINE_LINUX_DEFAULT} resume=UUID=$ROOT_UUID resume_offset=$RESUME_OFFSET"
EOF

Verify:

cat /etc/default/grub.d/99-hibernate.cfg

You should see:

GRUB_CMDLINE_LINUX_DEFAULT="${GRUB_CMDLINE_LINUX_DEFAULT} resume=UUID=<YOUR_ROOT_UUID> resume_offset=<YOUR_RESUME_OFFSET>"

8. Rebuild Initramfs and GRUB

Run:

sudo update-initramfs -u -k all

Then:

sudo update-grub

Some Linux Mint installations may display a warning similar to:

W: initramfs-tools configuration sets RESUME=UUID=...
W: but no matching swap device is available.

This can happen with swapfile-based hibernation because the resume device is the filesystem partition containing the swapfile, rather than a dedicated swap partition.

Do not assume that warning alone means the configuration failed.

Verify that GRUB contains the expected parameters:

sudo grep -oE 'resume=[^ ]+|resume_offset=[^ ]+' \
  /boot/grub/grub.cfg | sort -u

Expected:

resume=UUID=<YOUR_ROOT_UUID>
resume_offset=<YOUR_RESUME_OFFSET>

9. Reboot Once

Perform one normal reboot:

sudo reboot

This loads the newly configured kernel parameters.

After logging back in, verify:

echo "===== KERNEL COMMAND LINE ====="
cat /proc/cmdline

echo
echo "===== SWAP ====="
swapon --show

echo
echo "===== RESUME DEVICE ====="
cat /sys/power/resume

echo
echo "===== RESUME OFFSET ====="
cat /sys/power/resume_offset

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