Linux – Why can’t a file as swap be used for hibernation in Linux

hibernatelinuxswap

I was trying to hibernate my Fedora 27 system temporarily using a swap file and failed. Answers in the following question also say that a dedicated swap partition must be used to hibernate the system and a swap file won't work.

Why does Linux use a swap partition rather than a file?

I'm using an ext3 file system in which I created the swap file. What is stopping it being used for hibernation?

Best Answer

As said here (link provided by @don_crissti), the system must locate the swap file's header, but in order to do this the filesystem that contains the swap file must be mounted, and a journaled filesystem (as ext3 is) cannot be mounted during resume from disk.

Quoting from the document:

In order to use a swap file with swsusp, you need to:

1) Create the swap file and make it active, eg.

# dd if=/dev/zero of=<swap_file_path> bs=1024 count=<swap_file_size_in_k>

# mkswap <swap_file_path>

# swapon <swap_file_path>

2) Use an application that will bmap the swap file with the help of the FIBMAP ioctl and determine the location of the file's swap header, as the offset, in <PAGE_SIZE> units, from the beginning of the partition which holds the swap file.

3) Add the following parameters to the kernel command line:

resume=<swap_file_partition> resume_offset=<swap_file_offset>

where <swap_file_partition> is the partition on which the swap file is located and <swap_file_offset> is the offset of the swap header determined by the application in 2) (of course, this step may be carried out automatically by the same application that determines the swap file's header offset using the FIBMAP ioctl)

OR

Use a userland suspend application that will set the partition and offset with the help of the SNAPSHOT_SET_SWAP_AREA ioctl described in Documentation/power/userland-swsusp.txt (this is the only method to suspend to a swap file allowing the resume to be initiated from an initrd or initramfs image).

Related Solutions

Linux – Hibernation not working on Linux Mint 19

Linux Mint 19 does not support hibernation out of the box as per a Guide article in the Mint Forums.

The standard hibernation configuration will fail if your swap file is not in /swapfile or if you do not have a swap partition. A RedHat article provides some additional guidance on swap sizing.

If there is not enough room in the swap file or partition for the contents of your RAM plus whatever else you may have swapped out already, hibernation will fail, since the kernel writes a hibernation image of a size up to 2/5 the size of your RAM. As a rule of thumb, simply set up your swap file to at least the size of your RAM, or even double your RAM on systems with very low total RAM (since you are more likely to swap).

Please run this in a terminal window: free -h then swapon to confirm the swap file is large enough. If it is not large enough, expand the swap file. If it is, please proceed with:

RESUME_PARAMS="resume=UUID=$(findmnt / -o UUID -n) resume_offset=$(sudo filefrag -v /swapfile|awk 'NR==4{gsub(/\./,"");print $4;}') "  

if grep resume /etc/default/grub>/dev/null; then echo -e "\nERROR: Hibernation already configured. Remove the existing configuration from /etc/default/grub and add these parameters instead:\n$RESUME_PARAMS";else sudo sed -i "s/GRUB_CMDLINE_LINUX_DEFAULT=\"/GRUB_CMDLINE_LINUX_DEFAULT=\"$RESUME_PARAMS/" /etc/default/grub;fi

Unless there is an error message, then do sudo update-grub; if there are error messages, follow their instructions before performing sudo update-grub.

Lastly, add Hibernation to the GRUB2 menu with

sudo tee /etc/polkit-1/localauthority/50-local.d/com.ubuntu.enable-hibernate.pkla <<'EOB' [Enable hibernate] Identity=unix-user:* Action=org.freedesktop.login1.hibernate;org.freedesktop.login1.handle-hibernate-key;org.freedesktop.login1;org.freedesktop.login1.hibernate-multiple-sessions ResultActive=yes EOB

Best Answer

Related Solutions

Linux – Hibernation not working on Linux Mint 19

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