/proc/cpuinfo

[valevalorin]

I have a few questions about this file.

1. When does this file get generated?

2. Is this file accessible if I move the SD card from the RPI to another machine?

[ShiftPlusOne]

The file never physically exist on the card at all and is generated when it's read.

http://www.tldp.org/LDP/Linux-Filesyste ... /proc.html

[valevalorin]

So if I were to try and read this on a different machine, the file wouldn't exist?

[ShiftPlusOne]

If you mount the on /media/sd and try reading /media/sd/proc/cpuinfo, you will find that there's nothing there. If you read /proc/cpuinfo, you will get the cpuinfo for the host machine.

[DougieLawson]

1. When does this file get generated?

It's a virtual filesystem generated by the Linux kernel when it boots.
The code that writes the data to /proc/cpuinfo is ../linux/arch/arm/kernel/setup.c

[valevalorin]

Alright then, thanks a lot guys!

[valevalorin]

I actually have another question: can I use chmod on cpuinfo?

[DougieLawson]

No.

You can do awful things

Code: Select all

#!/bin/sh
cat /proc/cpuinfo | sed -e 's/Serial.*/Serial\t\t: 00000000deadbeef/g'  > /tmp/cpuinfo_fake
mount -o bind /tmp/cpuinfo_fake /proc/cpuinfo
mount -o remount,ro,bind /proc/cpuinfo

[valevalorin]

Is there some other way I can make cpuinfo only accessible by root? Is it only accessible by root by default?

[ShiftPlusOne]

What are you doing and why?

[DougieLawson]

Is there some other way I can make cpuinfo only accessible by root? Is it only accessible by root by default?

Rewrite the kernel modules and build your own kernel. But, you WILL break lots of things that expect cpuinfo to be world readable.

There's nothing in cpuinfo that can be used for any sensible security or encryption purposes. If you're thinking about hiding the CPUID, you've failed at the first fence. The bottom six digits are used for the MAC address for the eth0 interface. I can also get it with dmesg | grep serial.

[Joe Schmoe]

Change the password on 'pi' (and any other 'user' accounts you may have created).

That will keep those pesky users from accessing /proc/cpuinfo (or anything else).

[jojopi]

I actually have another question: can I use chmod on cpuinfo?

Yes, you can use chmod to restrict read access (but not to make the file meaningfully writeable). You will have to repeat it every boot, because the permissions are not stored on disk.

(Of course, I doubt it helps you.)