The most striking factor about the /proc file system is the fact that the
file system doesn't exist on any particular media. The /proc File System
is a pseudo file system residing in the virtual memory and
maintains highly dynamic data on the state of your operating system. Most
of the information in the /proc file system is updated to match the
current state of the operating system. The contents of the /proc file
system can be read by anyone who has the requisite permissions. However,
certain parts of the /proc file system can be read only by the owner of
the process and of course root. The contents of the /proc filesystem are
used by many utilities which grab the data from the particular /proc
directory and display it.
Under Linux, we have utilities like lscpi, scanpci and pnpdump which help
us detect the various PCI, ISA hardware chipsets and help us make the best
choices as far as the io, dma and irq values are concerned. Similarly by
looking at the values of the various parameters in the /proc file system,
one can determine a lot about the current state of the kernel and the
processes under way. For example, we have the dmesg command.
Dmesg helps us determine the devices that have been detected and
initialized by the Linux kernel. We have utilities like "ps" and "top"
which give an accurate snapshot about the status of the processes running
on the machine and a list of awake and sleeping processes currently
running on the machine. Have you ever wondered where exactly the
information dished out to you by the "ps" and the "top" process comes
from? The information for these processes come from the /proc file system
which is updated on the fly as changes take place in the processes.
Lets take a look at a snapshot of the directory listing of the root (/)
directory of a Linux machine.
drwxr-xr-x 14 root root 291 Oct 25 18:47 opt
dr-xr-xr-x 86 root root 0 Nov 30 2000 proc <--
drwx--x--x 16 root root 841 Nov 20 00:10 root
drwxr-xr-x 5 root root 4627 Oct 15 11:42 sbin
Since the /proc file system is a virtual file system and resides in
memory, a new /proc file system is created every time your Linux machine
reboots. Take a look at the snapshot of the root directory shown above.
The size of the proc directory is 0 and the last time of modification is
the current date.