Bug#1027915: systemd requires /run to be mounted with a minimum size of 20MB

[Helge Deller]

Package: systemd
Version: 252.4-1
Severity: important

Systemd mounts the /run tmpfs filesystem at bootup with a given/calculated size (I assume ~ 10% of free memory?).
The problem is, that this size needs to be at least 16MB (probaly better 20MB), because otherwise
systemd refuses to reload when exiting emergency mode.

I noticed that problem on my hppa machine.
It has 160MB RAM (which is not much of course).
Anyway, on this machine systemd had mounted /run at bootup with ~15MB:
tmpfs on /run type tmpfs (rw,nosuid,nodev,noexec,relatime,size=14812k,mode=755)
During bootup the system failed to mount some other drive and thus fell into emergency mode.
I then entered the password to enter the shell, mounted the drive and exited the shell to
continue with normal bootup, but then systemd reported:
...
Reloading system manager configuration
Failed to reload daemon: Refusing to reload, not enough space available on /run/systemd. Currently, 14.2M are free, but a safety buffer of 16.0M is enforced.
Starting default.target
...
My suggestion:
Please check that the /run mountpoint is mounted with at least 20MB, independend
of the installed RAM memory in the machine...

Thanks!
Helge

[Helmut Grohne]

Control: reassign -1 initramfs-tools-core

Hi Helge,

On Wed, Jan 04, 2023 at 02:08:00PM +0100, Helge Deller wrote:
> My suggestion:
> Please check that the /run mountpoint is mounted with at least 20MB, independend
> of the installed RAM memory in the machine...

Your suggestion makes sense in principle. However, it is
/usr/share/initramfs-tools/init that performs the mount, so that's what
would need changing.

As a workaround for your situation, I suggest adding a kernel parameter
initramfs.runsize=20M.

Would you be able to provide a patch here? I think that if a runsize is
given, it should be honoured, so it would probably work like:

if test -z "$RUNSIZE"; then
if system_has_at_least_200mb_ram; then
RUNSIZE=10%
else
RUNSIZE=20M
fi
fi

Helmut

[Helge Deller]

Hi Helmut,

On 1/4/23 14:26, Helmut Grohne wrote:
> On Wed, Jan 04, 2023 at 02:08:00PM +0100, Helge Deller wrote:
>> My suggestion:
>> Please check that the /run mountpoint is mounted with at least 20MB, independend
>> of the installed RAM memory in the machine...
>
> Your suggestion makes sense in principle. However, it is
> /usr/share/initramfs-tools/init that performs the mount, so that's what
> would need changing.

Ah, ok. Thanks Helmut!

> As a workaround for your situation, I suggest adding a kernel parameter
> initramfs.runsize=20M.

Yes, that should work.

> Would you be able to provide a patch here? I think that if a runsize is
> given, it should be honoured, so it would probably work like:
>
> if test -z "$RUNSIZE"; then
> if system_has_at_least_200mb_ram; then
> RUNSIZE=10%
> else
> RUNSIZE=20M
> fi
> fi

Yes, I'll try to send a patch.
I just wonder, what's the best way to get the amount of physical memory?
Something like this should work which gives size in kB:
mem_kb=$(grep MemTotal /proc/meminfo | (read txt mem txt2; echo $mem)) && echo $mem_kb

Is there a better way? I think glibc isn't running in initramfs, so "getconf _PHYS_PAGES" will probably not work?

Helge

[Helge Deller]

The attached patch ensures that the /run mount point
is always mounted with at least 20MB.

This is important since systemd requires at least 16MB
in /run, otherwise it will give errors and warnings and
will refuse to boot further after an emergency shell.

This patch has been tested on x86 (with VirtualBox VMs)
in configurations with 160MB RAM and 900MB RAM, as well
on a debian parisc installation with 160MB RAM.

This patch will adapt the size of /run, even if the
default value of 10% (of physical memory) is given
in the /etc/initramfs-tools/update-initramfs.conf file
(e.g. on x86).

Please apply to the next initramfs-tools update.

Signed-off-by: Helge Deller <del...@gmx.de>

[Helmut Grohne]

Hi Helge,

On Mon, Jan 23, 2023 at 10:48:27PM +0100, Helge Deller wrote:
> --- ./init.org 2023-01-23 21:40:33.079738389 +0000
> +++ ./init 2023-01-23 21:40:45.983861851 +0000
> @@ -205,6 +205,15 @@ else
> resume=${RESUME:-}
> fi
>
> +if [ -z "${RUNSIZE}" ] || [[ "${RUNSIZE}" \< "20" ]]; then

This is as bashism and init runs with dash as far as I can see.

Also note that RUNSIZE may legitimately be given as "1g" or "19%", both
of which should work. I suggest just not handling the case where RUNSIZE
is set by the user and letting them break their system however they
like rather than risk breaking legitimate configuration.

> + read MemTotal mem_kb rest < /proc/meminfo
> + # systemd requires at minumum 16MB for /run, so reserve
> + # 20MB for machines which have less than 200MB RAM
> + if [ "$mem_kb" -lt "200000" ]; then
> + RUNSIZE=20M # for machines <= 200MB RAM

Given that you initialize a default here, I think it would make the code
more obvious if you pulled the 10% default 4 lines later into an else
branch.

> + fi
> +fi
> +
> mount -t tmpfs -o "nodev,noexec,nosuid,size=${RUNSIZE:-10%},mode=0755" tmpfs /run
> mkdir -m 0700 /run/initramfs

Helmut

[Helge Deller]

Hi Helmut,

On 1/24/23 06:27, Helmut Grohne wrote:
> On Mon, Jan 23, 2023 at 10:48:27PM +0100, Helge Deller wrote:
>> --- ./init.org 2023-01-23 21:40:33.079738389 +0000
>> +++ ./init 2023-01-23 21:40:45.983861851 +0000
>> @@ -205,6 +205,15 @@ else
>> resume=${RESUME:-}
>> fi
>>
>> +if [ -z "${RUNSIZE}" ] || [[ "${RUNSIZE}" \< "20" ]]; then
>
> This is as bashism and init runs with dash as far as I can see.

Hmm... I did tested it, at it seemed to work...
Which part of that line exactly do you think is problematic?
I'm open for any other idea how to code it.

> Also note that RUNSIZE may legitimately be given as "1g" or "19%", both
> of which should work.

Both will work, because I assume that on such systems you probably have more than 200MB RAM
and thus my patch won't touch the user-provided value at all.

> I suggest just not handling the case where RUNSIZE
> is set by the user

Yes, I fully agree with you and had hoped to implement it that way.
Ideally RUNSIZE shouldn't be changed if it was already provided.
But the problem is, that on some/many systems RUNSIZE is *automatically* provided and added to
the bootloader via a default value (of 10%) given in /etc/initramfs-tools/update-initramfs.conf.
So, even if the user didn't changed or provided anything, the 10% is always set
and thus my check would never trigger....

> and letting them break their system however they
> like rather than risk breaking legitimate configuration.

Again, the default value is the problem...

>> + read MemTotal mem_kb rest < /proc/meminfo
>> + # systemd requires at minumum 16MB for /run, so reserve
>> + # 20MB for machines which have less than 200MB RAM
>> + if [ "$mem_kb" -lt "200000" ]; then
>> + RUNSIZE=20M # for machines <= 200MB RAM
>
> Given that you initialize a default here, I think it would make the code
> more obvious if you pulled the 10% default 4 lines later into an else
> branch.

Not sure I understand this...?

>> + fi
>> +fi
>> +
>> mount -t tmpfs -o "nodev,noexec,nosuid,size=${RUNSIZE:-10%},mode=0755" tmpfs /run
>> mkdir -m 0700 /run/initramfs
>
> Helmut

Thank you Helmut!
Helge

[Helmut Grohne]

Hi Helge,

On Tue, Jan 24, 2023 at 10:30:37PM +0100, Helge Deller wrote:
> On 1/24/23 06:27, Helmut Grohne wrote:
> > On Mon, Jan 23, 2023 at 10:48:27PM +0100, Helge Deller wrote:
> > > --- ./init.org 2023-01-23 21:40:33.079738389 +0000
> > > +++ ./init 2023-01-23 21:40:45.983861851 +0000
> > > @@ -205,6 +205,15 @@ else
> > > resume=${RESUME:-}
> > > fi
> > >
> > > +if [ -z "${RUNSIZE}" ] || [[ "${RUNSIZE}" \< "20" ]]; then
> >
> > This is as bashism and init runs with dash as far as I can see.
>
> Hmm... I did tested it, at it seemed to work...
> Which part of that line exactly do you think is problematic?
> I'm open for any other idea how to code it.

The lexicographic comparison is outside the realm of POSIX shell, but to
my surprise this actually is supported by dash. So fixing this would be
academic.

> Both will work, because I assume that on such systems you probably have more than 200MB RAM
> and thus my patch won't touch the user-provided value at all.

Fair enough.

> > > + read MemTotal mem_kb rest < /proc/meminfo
> > > + # systemd requires at minumum 16MB for /run, so reserve
> > > + # 20MB for machines which have less than 200MB RAM
> > > + if [ "$mem_kb" -lt "200000" ]; then
> > > + RUNSIZE=20M # for machines <= 200MB RAM

else
: "${RUNSIZE:=10%}"

> >
> > Given that you initialize a default here, I think it would make the code
> > more obvious if you pulled the 10% default 4 lines later into an else
> > branch.
>
> Not sure I understand this...?
>
> > > + fi
> > > +fi
> > > +
> > > mount -t tmpfs -o "nodev,noexec,nosuid,size=${RUNSIZE:-10%},mode=0755" tmpfs /run

This is the other line that contains a default. I suggested moving this
default up to make it more obvious, but this is really only a cosmetic
improvement.

As such LGTM, but I am not an initramfs maintainer.

Helmut