Is there a "recipe" for adding a hardware swap partition to an
existing RasPiOS installation? Ideally I'd like a traditional
layout, with swap situated between / and /usr. I know how to
do it with FreeBSD during the install process but this particular
case involves a running, somewhat valuable RasPiOS installation
and the tools offered on RasPiOS are different enough to warrant
a study of prior art if it's available.

What I'd like to do is resize the existing root to roughly its
present, occupied size, add a swap partition in the freed space
and then create /usr in the remaining space, copying the old
/usr to the new, cleaning out usr files from the original root
partition and mounting the new /usr on the empty mountpoint.

This needs to be done under single-user mode and I don't know
how to get at single-user in RasPiOS. It could be done via booting
from a microSD, but that pitches me into the installer which isn't
exactly familiar territory.

In case it matters, this is on an 8GB Pi5 running Bookworm with
dual monitors and a 1 TB mechanical hard drive. df reports

Filesystem 1K-blocks Used Available Use% Mounted on
udev 4081296 0 4081296 0% /dev
tmpfs 1650304 6512 1643792 1% /run
/dev/sda2 961067256 61907904 850331260 7% /
tmpfs 4125728 163136 3962592 4% /dev/shm
tmpfs 5120 48 5072 1% /run/lock
/dev/sda1 522230 79520 442710 16% /boot/firmware
tmpfs 825136 272 824864 1% /run/user/1000

The need for "real" swap arises when Chromium and Firefox are both
running with multiple tabs open.

Thanks for reading, and any suggestions!

bob prohaska


--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Wed, 11 Mar 2026 16:20:15 -0000 (UTC), bp wrote:

This needs to be done under single-user mode and I don't know
how to get at single-user in RasPiOS.

This is done by modifying the kernel command line -- there should be a bootloader option to do this on a one-time basis before actually
loading the kernel.

The option ?single? should do the trick, though I think it will prompt
for the root password before allowing you in.

Another option to try is ?init=/bin/bash?.

These options should be common across Linux kernels, independent of architecture or bootloader.

--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 11/03/2026 16:20, bp@www.zefox.net wrote:

Is there a "recipe" for adding a hardware swap partition to an
existing RasPiOS installation? Ideally I'd like a traditional
layout, with swap situated between / and /usr. I know how to
do it with FreeBSD during the install process but this particular
case involves a running, somewhat valuable RasPiOS installation
and the tools offered on RasPiOS are different enough to warrant
a study of prior art if it's available.

What I'd like to do is resize the existing root to roughly its
present, occupied size, add a swap partition in the freed space
and then create /usr in the remaining space, copying the old
/usr to the new, cleaning out usr files from the original root
partition and mounting the new /usr on the empty mountpoint.

This needs to be done under single-user mode and I don't know
how to get at single-user in RasPiOS. It could be done via booting
from a microSD, but that pitches me into the installer which isn't
exactly familiar territory.

I don't think that is necessarily true.

If you create a bootable SD card, you can do all you want to the sda
disk whilst it's online

You could also create a swap file in / and add that as an alternative

In case it matters, this is on an 8GB Pi5 running Bookworm with
dual monitors and a 1 TB mechanical hard drive. df reports

Filesystem 1K-blocks Used Available Use% Mounted on
udev 4081296 0 4081296 0% /dev
tmpfs 1650304 6512 1643792 1% /run
/dev/sda2 961067256 61907904 850331260 7% /
tmpfs 4125728 163136 3962592 4% /dev/shm
tmpfs 5120 48 5072 1% /run/lock
/dev/sda1 522230 79520 442710 16% /boot/firmware
tmpfs 825136 272 824864 1% /run/user/1000

The need for "real" swap arises when Chromium and Firefox are both
running with multiple tabs open.

Yaj well no fine

I'd add a swap file. work of a few minutes only

$ dd if=/dev/zero of=/path/to/swapfile bs=1M count=1024 # For 1GB swap file
$ mkswap /path/to/swapfile
$ swapon /path/to/swapfile

Thanks for reading, and any suggestions!

bob prohaska

--
Climate is what you expect but weather is what you get.
Mark Twain


--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

Newsgroups: comp.sys.raspberry-pi
From: Jim Jackson <jj@franjam.org.uk>
Subject: Re: Adding a hardware swap partition
References: <10os4nv$17t1j$1@dont-email.me>
Followup-To:

On 2026-03-11, bp@www.zefox.net <bp@www.zefox.net> wrote:

Is there a "recipe" for adding a hardware swap partition to an
existing RasPiOS installation? Ideally I'd like a traditional
layout, with swap situated between / and /usr.

AFAIK modern PIOS versions all use merged /usr, as they are based on
debian which /usr merged. This means that the /usr directory has to
reside on the root partition. I usually put my swap partition between
root and /home partitions.

I'm assuming your PIOS is running systemd so try looking at

man systemd.swap

I remember that on a SYSV init system I think I ran mkswap on the disk partition, then added an entry to /etc/fstab like

/dev/sda2 none swap sw 0 0

and just rebooted.

I tend to use a swap file nowadays.

cheers
Jim







--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Thu, 12 Mar 2026 15:37:29 -0000 (UTC), bp wrote:

Lawrence D?Oliveiro <ldo@nz.invalid> wrote:

This is done by modifying the kernel command line -- there should
be a bootloader option to do this on a one-time basis before
actually loading the kernel.

I can understand editing cmdline.txt and rebooting as a way to get
single user ...

No, this is using one of the options in the bootloader menu
(?advanced?, I think it is) to do a one-time edit to the command line
for that boot. You don?t want to permanently put the system to booting
into single-user mode every time, do you?

--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

Lawrence D?Oliveiro <ldo@nz.invalid> wrote:

On Wed, 11 Mar 2026 16:20:15 -0000 (UTC), bp wrote:

This needs to be done under single-user mode and I don't know
how to get at single-user in RasPiOS.

This is done by modifying the kernel command line -- there should be a bootloader option to do this on a one-time basis before actually
loading the kernel.

The option ?single? should do the trick, though I think it will prompt
for the root password before allowing you in.

Another option to try is ?init=/bin/bash?.

These options should be common across Linux kernels, independent of architecture or bootloader.

I can understand editing cmdline.txt and rebooting as a way to get single
user, but by the time there's anything visible on the monitor the kernel
is already starting services and well past any opportunity to intervene.

It looks as if swap files have their advocates. Just how much slower is
a swap file? It certainly looks easier and might be a good experiment.

Thanks to everybody for replying!

bob prohaska


--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

Lawrence D?Oliveiro <ldo@nz.invalid> wrote:

On Thu, 12 Mar 2026 15:37:29 -0000 (UTC), bp wrote:

Lawrence D?Oliveiro <ldo@nz.invalid> wrote:

This is done by modifying the kernel command line -- there should
be a bootloader option to do this on a one-time basis before
actually loading the kernel.

I can understand editing cmdline.txt and rebooting as a way to get
single user ...

No, this is using one of the options in the bootloader menu
(?advanced?, I think it is) to do a one-time edit to the command line
for that boot.

I'm not familiar with such a menu, how is it invoked?

You don?t want to permanently put the system to booting
into single-user mode every time, do you?

No, but I could edit cmdline.txt, reboot to single-user,
finish my business, re-edit cmdline.txt and reboot again.

I was hopeful somebody would respond to my query regarding
the relative speeds of swapfiles vs swap partitions. If
they're anywhere close in performance a swapfile seems
worth trying.

Thanks for writing!

bob prohaska


--- PyGate Linux v1.5.12
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 13/03/2026 01:26, bp@www.zefox.net wrote:

I was hopeful somebody would respond to my query regarding
the relative speeds of swapfiles vs swap partitions. If
they're anywhere close in performance a swapfile seems
worth trying.

That is an interesting thought.

Google AI sez

"Key Differences and Performance Factors:

- Performance: A swap partition is technically faster as it writes
directly to the disk, bypassing the filesystem, but this advantage is
rarely noticeable in daily use.

- Flexibility: Swap files are much easier to resize, create, or delete without modifying disk partitions, making them the preferred choice for
most modern setups.

- Fragmentation: On traditional HDDs, a fragmented swap file can be
slower, but this is not an issue on SSDs.

- Hard Drive Placement: On spinning HDDs, a partition placed at the
start of the drive is slightly faster, but this does not apply to SSDs.

Recommendation:

For the majority of users (especially on SSDs), a swap file is
recommended for its convenience without any meaningful loss in speed. A
swap partition is only recommended if you have specific,
high-performance needs or are using older, heavily fragmented hard drives. "

I think that is an interesting summary, the point being made that speed
is dominated today by disk access times, not CPU cycles in addressing a
file system.
And with the demise of spinning rust, there is no seek delay either, so
the theoretical advantages of an actual partition in the disks low
sector area, no longer outweigh the operational simplicity of a swap file.

Like so many other things that grew out of limited RAM and slow spinning
rust disks, the swap partition is really no longer necessary...


--
?People believe certain stories because everyone important tells them,
and people tell those stories because everyone important believes them. Indeed, when a conventional wisdom is at its fullest strength, one?s
agreement with that conventional wisdom becomes almost a litmus test of
one?s suitability to be taken seriously.?

Paul Krugman


--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

The Natural Philosopher <tnp@invalid.invalid> wrote:

On 13/03/2026 14:16, Theo wrote:

The Natural Philosopher <tnp@invalid.invalid> wrote:

I think that is an interesting summary, the point being made that speed
is dominated today by disk access times, not CPU cycles in addressing a >> file system.
And with the demise of spinning rust, there is no seek delay either, so
the theoretical advantages of an actual partition in the disks low
sector area, no longer outweigh the operational simplicity of a swap file. >>
Like so many other things that grew out of limited RAM and slow spinning >> rust disks, the swap partition is really no longer necessary...

One advantage of a swap partition is that it's a dedicated space - if you start running low on space it may limit the size of swapfile that can be created, which has a knock-on impact on performance.

I dont think you understand the nature of a swapfile.

It is a fixed length file.

Ah, it seems only Windows does variable length files.

Depending on the filesystem the swapfile may not be backed by physical
blocks, ie the file exists but the space is not preallocated. It looks like you have to explicitly force that.

Another reason is if you're using hibernate. You need swap space at least as large as RAM to save out your memory contents to, so that can prevent hibernate working if you are running low on space. Also hibernate/restore is a fairly low-level process and swap partitions are easier to setup for that than swap files.

Again, you are talking bollocks. Swap files are pre-allocated, of fixed size, and zero filled.

For swap files, hibernation appears to be more complicated:

https://wiki.debian.org/Hibernation/Hibernate_Without_Swap_Partition

indicates you need to tell the kernel the offset of the swapfile within the partition, which suggests that the kernel is reading it directly rather than via the filesystem. That implies the filesystem must allocate it
contiguously and is not allowed to have any kind of fragmentation. That
means it could be impossible to set up on a machine that's been running a while.

Theo

--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 2026-03-11 at 13:20 ADT, bp@www.zefox.net <bp@www.zefox.net> wrote:

What I'd like to do is resize the existing root to roughly its
present, occupied size,

I think you will rue that decision later, unless you are sure that you are never going to add more packages (which will occupy some space in /etc and /var, even with the bulk of the space being in /usr), never do updates
which may use more space in /boot, /etc/ or /var, and so on.

I haven't had a separate /usr partition on any system in a long time (and
I'm wondering why you want to do that), so I can't give any helpful amounts
on the minimum extra space you should leave. But I strongly advise you to
give yourself enough extra space in / to handle future updates to your
system.

Jim

--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

The Natural Philosopher <tnp@invalid.invalid> wrote:

I think that is an interesting summary, the point being made that speed
is dominated today by disk access times, not CPU cycles in addressing a file system.
And with the demise of spinning rust, there is no seek delay either, so
the theoretical advantages of an actual partition in the disks low
sector area, no longer outweigh the operational simplicity of a swap file.

Like so many other things that grew out of limited RAM and slow spinning rust disks, the swap partition is really no longer necessary...

One advantage of a swap partition is that it's a dedicated space - if you
start running low on space it may limit the size of swapfile that can be created, which has a knock-on impact on performance.

Another reason is if you're using hibernate. You need swap space at least
as large as RAM to save out your memory contents to, so that can prevent hibernate working if you are running low on space. Also hibernate/restore
is a fairly low-level process and swap partitions are easier to setup for
that than swap files.

Theo

--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 13/03/2026 14:16, Theo wrote:

The Natural Philosopher <tnp@invalid.invalid> wrote:

I think that is an interesting summary, the point being made that speed
is dominated today by disk access times, not CPU cycles in addressing a
file system.
And with the demise of spinning rust, there is no seek delay either, so
the theoretical advantages of an actual partition in the disks low
sector area, no longer outweigh the operational simplicity of a swap file. >>
Like so many other things that grew out of limited RAM and slow spinning
rust disks, the swap partition is really no longer necessary...

One advantage of a swap partition is that it's a dedicated space - if you start running low on space it may limit the size of swapfile that can be created, which has a knock-on impact on performance.

I dont think you understand the nature of a swapfile.

It is a fixed length file.

Another reason is if you're using hibernate. You need swap space at least
as large as RAM to save out your memory contents to, so that can prevent hibernate working if you are running low on space. Also hibernate/restore
is a fairly low-level process and swap partitions are easier to setup for that than swap files.

Again, you are talking bollocks. Swap files are pre-allocated, of fixed
size, and zero filled.

Theo

--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone




--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 2026-03-13 02:26, bp@www.zefox.net wrote:

I was hopeful somebody would respond to my query regarding
the relative speeds of swapfiles vs swap partitions. If
they're anywhere close in performance a swapfile seems
worth trying.

Run:
vmstat -t 10 60
in a terminal while you are doing your daily tasks in other
windows to see how much swap I/O there really is.

This command does 60 measurements with an interval of 10
seconds, the si and so columns show the swap I/O.

Usually it is not much, so I wouldn't worry too much about
performance.
--
Regards,
Kees

--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 13/03/2026 18:28, Theo wrote:

The Natural Philosopher <tnp@invalid.invalid> wrote:

On 13/03/2026 14:16, Theo wrote:

The Natural Philosopher <tnp@invalid.invalid> wrote:

I think that is an interesting summary, the point being made that speed >>>> is dominated today by disk access times, not CPU cycles in addressing a >>>> file system.
And with the demise of spinning rust, there is no seek delay either, so >>>> the theoretical advantages of an actual partition in the disks low
sector area, no longer outweigh the operational simplicity of a swap file. >>>>
Like so many other things that grew out of limited RAM and slow spinning >>>> rust disks, the swap partition is really no longer necessary...

One advantage of a swap partition is that it's a dedicated space - if you >>> start running low on space it may limit the size of swapfile that can be >>> created, which has a knock-on impact on performance.

I dont think you understand the nature of a swapfile.

It is a fixed length file.

Ah, it seems only Windows does variable length files.

Depending on the filesystem the swapfile may not be backed by physical blocks, ie the file exists but the space is not preallocated. It looks like you have to explicitly force that.

I posted the magic spell
you create a file and write the required length using dd with zeros.

sudo dd if=/dev/zero of=/var/swapfile bs=1K count=4M etc.

Another reason is if you're using hibernate. You need swap space at least >>> as large as RAM to save out your memory contents to, so that can prevent >>> hibernate working if you are running low on space. Also hibernate/restore >>> is a fairly low-level process and swap partitions are easier to setup for >>> that than swap files.

Again, you are talking bollocks. Swap files are pre-allocated, of fixed
size, and zero filled.

For swap files, hibernation appears to be more complicated:

https://wiki.debian.org/Hibernation/Hibernate_Without_Swap_Partition

indicates you need to tell the kernel the offset of the swapfile within the partition, which suggests that the kernel is reading it directly rather than via the filesystem. That implies the filesystem must allocate it contiguously and is not allowed to have any kind of fragmentation. That means it could be impossible to set up on a machine that's been running a while.

Raspberry Pi OS (RaspiOS) does not natively support traditional ACPI hibernation (suspend-to-disk) out of the box

Because Raspberry Pi lacks proper ACPI support, traditional hibernation
is difficult and often requires a custom kernel, though it is "in
theory" possible.

Workaround: Users often use a swapfile combined with systemd-sleep to enable this functionality.

GPIO Shutdown: A common "shutdown" alternative is to connect a button
to GPIO3 to perform a safe shutdown rather than true hibernation.

Theo

--
?It is dangerous to be right in matters on which the established
authorities are wrong.?

? Voltaire, The Age of Louis XIV


--- PyGate Linux v1.5.13
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)