Linux Pocket Guide, 2nd Edition

Operating System Directories

Some directories support the Linux kernel, the lowest-level part of the Linux operating system.

/boot

Files for booting the system. This is where the kernel lives, typically named /boot/vmlinuz.

/lost+found

Damaged files that were rescued by a disk recovery tool.

/proc

Describes currently running processes; for advanced users.

The files in /proc provide views into the running kernel and have special properties. They always appear to be zero sized, read-only, and dated now:

$ ls -l /proc/version
-r--r--r--   1 root   root    0 Oct  3 22:55 /proc/version

However, their contents magically contain information about the Linux kernel:

$ cat /proc/version
Linux version 2.6.32-71.el6.i686 ...

Files in /proc are used mostly by programs, but feel free to explore them. Here are some examples:

/proc/ioports	A list of your computer’s input/output hardware.
/proc/version	The operating system version. The uname command prints the same information.
/proc/uptime	System uptime, i.e., seconds elapsed since the system was last booted. Run the uptime command for a more human-readable result.
/proc/nnn	Where nnn is a positive integer, information about the Linux process with process ID nnn.
/proc/self	Information about the current process you’re running; a symbolic link to a /proc/nnn file, automatically updated. Try ls -l /proc/self several times in a row: you’ll see /proc/self changing where it points.