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

...if your system fails to boot and you end up in maintenance mode there
is no way out except use of the root login and password...

Strange, if it can read the root password hash from storage, why
can't it read the other ones? Does RPi OS it store that password in
the initrd but not the other ones? When they can't mount the root
filesystem, I remember other Linux distros going to a command prompt
without asking for a password, though I haven't seen what RPi OS
does.

And if its a Pi zero you have to buy adapters to plug in a USB keyboard
to enter it on and an HDMI monitor to see what is going on.

A quick and cheap alternative is to cut a USB extension cable or
a lead from an old PC USB socket back-panel and solder it to the
test points with the USB signals on the bottom of the Pi Zero's
circuit board. For the monitor, solder wires or a header to the
composite video output which can be enabled in config.txt.

--
__ __
#_ < |\| |< _#

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

...if your system fails to boot and you end up in maintenance mode there
is no way out except use of the root login and password...

And if its a Pi zero you have to buy adapters to plug in a USB keyboard
to enter it on and an HDMI monitor to see what is going on.



--
?The urge to save humanity is almost always only a false face for the
urge to rule it.?
? H. L. Mencken

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

not@telling.you.invalid (Computer Nerd Kev) writes:

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

...if your system fails to boot and you end up in maintenance mode
there is no way out except use of the root login and password...

Strange, if it can read the root password hash from storage, why
can't it read the other ones? Does RPi OS it store that password in
the initrd but not the other ones? When they can't mount the root
filesystem, I remember other Linux distros going to a command prompt
without asking for a password, though I haven't seen what RPi OS
does.

I think TNP is seeing the emergency.service unit, which is run under
certain boot failure conditions. The effect is to run sulogin, which
normally requests the root password.

AFAICT if there is no root password set, sulogin will give you a root
shell without requesting any authentication.

Even if that doesn?t go as expected, you can edit the kernel command
line to point init at a shell, which will then run without any tedious
business with passwords, as long as it actually exists. So, there?s
definitely another way.

On an x86 device running Grub you can do this easily in the boot-time
UI. I don?t know if there?s an interactive way to do it on any Pi models
but in the worst case you could mount the SD card with another computer
and edit the kernel command line.

If boot fails before / is mounted then I think you get an initramfs
shell, without any authentication. Certainly my initramfs doesn?t
include any password hashes. I don?t feel like doing the experiment l-)

References:

https://man7.org/linux/man-pages/man7/systemd.special.7.html
https://man7.org/linux/man-pages/man8/sulogin.8.html
https://github.com/util-linux/util-linux/blob/master/login-utils/sulogin.c

--
https://www.greenend.org.uk/rjk/

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

Richard Kettlewell <invalid@invalid.invalid> wrote:

I think TNP is seeing the emergency.service unit, which is run under
certain boot failure conditions. The effect is to run sulogin, which
normally requests the root password.

AFAICT if there is no root password set, sulogin will give you a root
shell without requesting any authentication.

Yes. Ubuntu doesn't set a root password, so when you get that prompt to
enter the root password for maintenance you can just press Enter and you're
in.

Theo

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

On 25/03/2026 23:25, Richard Kettlewell wrote:

not@telling.you.invalid (Computer Nerd Kev) writes:

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

...if your system fails to boot and you end up in maintenance mode
there is no way out except use of the root login and password...

Strange, if it can read the root password hash from storage, why
can't it read the other ones? Does RPi OS it store that password in
the initrd but not the other ones? When they can't mount the root
filesystem, I remember other Linux distros going to a command prompt
without asking for a password, though I haven't seen what RPi OS
does.

I think TNP is seeing the emergency.service unit, which is run under
certain boot failure conditions. The effect is to run sulogin, which
normally requests the root password.

yes.

AFAICT if there is no root password set, sulogin will give you a root
shell without requesting any authentication.

ah.

Even if that doesn?t go as expected, you can edit the kernel command
line to point init at a shell, which will then run without any tedious business with passwords, as long as it actually exists. So, there?s definitely another way.

how? the machine is inaccessible

On an x86 device running Grub you can do this easily in the boot-time
UI. I don?t know if there?s an interactive way to do it on any Pi models
but in the worst case you could mount the SD card with another computer
and edit the kernel command line.

if you knew what to edit...

If boot fails before / is mounted then I think you get an initramfs
shell, without any authentication. Certainly my initramfs doesn?t
include any password hashes. I don?t feel like doing the experiment l-)

The error was in fstab. I *think* it mounted /

When I finally got in after buying the correct adapters, I was able to
edit things till it booted,.

References:

https://man7.org/linux/man-pages/man7/systemd.special.7.html
https://man7.org/linux/man-pages/man8/sulogin.8.html
https://github.com/util-linux/util-linux/blob/master/login-utils/sulogin.c

--
Any fool can believe in principles - and most of them do!




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

On 25/03/2026 22:20, Computer Nerd Kev wrote:

Strange, if it can read the root password hash from storage, why
can't it read the other ones?

You are never presented with an option to enter a name, only the root
password

--
Karl Marx said religion is the opium of the people.
But Marxism is the crack cocaine.


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

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

On 25/03/2026 23:25, Richard Kettlewell wrote:

Even if that doesn't go as expected, you can edit the kernel command
line to point init at a shell, which will then run without any tedious
business with passwords, as long as it actually exists. So, there's
definitely another way.

how? the machine is inaccessible

Edit cmdline.txt on the MicroSD card with a PC.

On an x86 device running Grub you can do this easily in the boot-time
UI. I don't know if there's an interactive way to do it on any Pi models
but in the worst case you could mount the SD card with another computer
and edit the kernel command line.

if you knew what to edit...

cmdline.txt, on the FAT partition. There's no Grub-style
interactive boot prompt, so you do need to edit the file.

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