/proc

alexrabbi · 06-04-2021, 09:07 AM

Hi All,

I am newbie here, I have quick question for which I could not get an answer anywhere.

I know that /Proc is a virtual file system and it stores system information and it is created on fly each time system boots up.

someone asked a question why is /proc created on fly ? why is it that way ?

I could not get a convincing answer anywhere. If anyone can explain, please do.

Regards,
Alex

shruggy · 06-04-2021, 09:48 AM

It's just a convenient interface provided by kernel following the Unix philosophy "everything is a file". This answers the question "Why is it a file system?" which is the correct one to ask.

pan64 · 06-04-2021, 10:42 AM

actually it does not store anything, but will give information about a living (running) system.

alexrabbi · 06-04-2021, 10:50 AM

Quote:

Originally Posted by shruggy

It's just a convenient interface provided by kernel following the Unix philosophy "everything is a file". This answers the question "Why is it a file system?" which is the correct one to ask.

Actually it was in an interview he asked me why is it created on fly and why is not a permanently residing on server ?

hazel · 06-04-2021, 10:58 AM

/proc isn't a real filesystem. It's a window into the running kernel dressed up as a filesystem for the user's convenience. It's created on the fly because each run of the kernel is different, at least potentially.

As well as info on the kernel, hardware drivers, etc., /proc contains the task structures created by the kernel for all running processes. These are the subdirectories with numbers for names. The numbers are the PIDs of the processes. Obviously this sort of info can't be permanently stored on disk.

pan64 · 06-04-2021, 12:38 PM

Quote:

Originally Posted by alexrabbi

Actually it was in an interview he asked me why is it created on fly and why is not a permanently residing on server ?

Because it is the state of the running system, which is [obviously] changing continuously.

syg00 · 06-04-2021, 05:08 PM

The reason it doesn't exist on disk is that it is created in kernel cache - i.e. in RAM. You (the user) don't have to worry about mounting it, what filesystem it uses ...

DavidMcCann · 06-05-2021, 10:39 AM

To make things a little clearer, consider this command

Code:

$: cat /proc/cpuinfo

Normally cat reads a file and copies the contents to the terminal. But there is no file there! What actually happens is that the OS gets the data represented by the name /proc/cpuinfo by sending a request to the CPU, which comes up with the information.

Now try

Code:

$: cat /proc/sys/kernel/sysrq

This asks the kernel if it recognises the "magic system request" key. If it replies "1" it does, if "0" it doesn't. This is one of the "entries" in /proc that you can actually alter (and that can sometimes be a dangerous thing to do!) with

Code:

$: echo 1 > /proc/sys/kernel/sysrq

To see the result, https://en.wikipedia.org/wiki/Magic_SysRq_key