1. Proc File System
Sadi Evren SEKER

2. Proc FS /proc /proc directory is NOT a real File System
It is a Virtual File System
information about processes and other system information.
It is mapped to /proc and mounted at boot time.

3. Discovering around # cd /proc
The first thing that you will notice is that there are some familiar sounding files, and then a whole bunch of numbered directories. The numbered directories represent processes, better known as PIDs, and within them, a command that occupies them. The files contain system information such as memory (meminfo), CPU information (cpuinfo), and available filesystems.

4. meminfo # cat /proc/meminfo
As you can see, /proc/meminfo contains a bunch of information about your system’s memory, including the total amount available (in kb) and the amount free on the top two lines.

5. Man Pages
# man 5 /proc/<filename>

6. List of Files /proc/cmdline – Kernel command line information.
/proc/console – Information about current consoles including tty.
/proc/devices – Device drivers currently configured for the running kernel.
/proc/dma – Info about current DMA channels.
/proc/fb – Framebuffer devices.
/proc/filesystems – Current filesystems supported by the kernel.
/proc/iomem – Current system memory map for devices.
/proc/ioports – Registered port regions for input output communication with device.
/proc/loadavg – System load average.

7. List of Files (continue)
/proc/locks – Files currently locked by kernel.
/proc/meminfo – Info about system memory (see above example).
/proc/misc – Miscellaneous drivers registered for miscellaneous major device.
/proc/modules – Currently loaded kernel modules.
/proc/mounts – List of all mounts in use by system.
/proc/partitions – Detailed info about partitions available to the system.
/proc/pci – Information about every PCI device.
/proc/stat – Record or various statistics kept from last reboot.
/proc/swap – Information about swap space.
/proc/uptime – Uptime information (in seconds).
/proc/version – Kernel version, gcc version, and Linux distribution installed.

8. Process Info
Within /proc’s numbered directories you will find a few files and links. Remember that these directories’ numbers correlate to the PID of the command being run within them. Let’s use an example. On my system, there is a folder name /proc/12:
# cd /proc/12
# ls

9. Process Status / Details
# cat /proc/12/status

10. Some important files
In any numbered directory, you will have a similar file structure. The most important ones, and their descriptions, are as follows:
cmdline – command line of the process
environ – environmental variables
fd – file descriptors
limits – contains information about the limits of the process
mounts – related information
You will also notice a number of links in the numbered directory:
cwd – a link to the current working directory of the process
exe – link to the executable of the process
root – link to the work directory of the process

11. Some commands
uptime, lsof, mount, and ps

12. Assignment
The number of CPUs in your machine and their clock speed, number of cores.
The version of Linux kernel running on your system
The time in day:hr:min:sec when the system was last booted
The average load on the system in the last 15 minutes
The total usable and currently free memory in the system
The total swap space and the currently used swap space in the system
The swap partitions and their sizes
The time the CPU spent (over all processes) in the user mode and kernel mode
The number of context switches made by the system so far
The number of interrupts handled by the system so far