The /proc File System And ProcMeter

You may rely on your electronic Rolodex to organize your life, but Linux uses the /proc file system.
Of What Use Is All This Information?

Most people are using /proc without realizing it. The programs top, ps, free and their friends all use /proc. The information that they provide is taken directly from /proc and formatted for display.

Compare the contents of the /proc/meminfo file (above) with the command free that gives output that looks like:

       total    used    free   shared  buffers
Mem:     11156    8680    2476    2724    2800
Swap:    25196    5204   19992

As you can see, this table is just a formatted version of the contents of /proc/meminfo.

The output of the ps program is all available in /proc; all of the information is stored in the per-process directories. Most of it just needs to be reasonably formatted for the user.

What is ProcMeter?

ProcMeter is a program that monitors the information stored in /proc. The information is displayed in a number of graphs. Each of these graphs shows one aspect of the system. The program runs under X Windows on Linux only.

Anybody who has used xload, xmeter or perfmeter will recognize this description. The difference is these programs use a system-independent method of obtaining data, whereas ProcMeter was designed for Linux from the start. When ProcMeter is using /proc, it is occupying minimal memory and taking negligible CPU time. Once /proc is used, other ideas for obtaining data spring to mind. Looking at the table of /proc above, we can see there is a lot of useful information available.

What Can ProcMeter Tell Me?

The statistics available in ProcMeter can be divided naturally into a number of classes.

  1. Processes—Basic information about the system, how busy it is and how heavily loaded it is. The processing power of the CPU is spread between all of the running processes and the kernel, and is idle for the remaining time.

cpu

is the total percentage of the CPU being used.

cpu-user

is the percentage of the CPU used by user processes.

cpu-nice

is the percentage of the CPU used by nice (low priority) processes.

cpu-sys

is the percentage of the CPU used by the kernel.

cpu-idle

is the percentage of the CPU unused (opposite of CPU).

load

is the system load, the number of running processes averaged over the previous minute.

proc

is the number of processes present on the system.

context

is the number of context switches between processes per second.

  1. Memory (Real and Virtual)--Memory is such a precious resource (especially on small PCs for the home user) that it is important to keep track of it. The beauty of the Unix system is that the use of virtual memory (swap space) is transparent. Transparent, that is, until your computer makes a noise like a coffee grinder, and programs start to crawl—this is a sure sign that you are out of real memory and living in the virtual stuff.

mem-free

is the amount of free RAM.

mem-used

is the amount of used RAM.

mem-buff

is the amount of RAM used for file buffers.

mem-cache

is the amount of RAM used as cache memory (kernel version 2.0).

mem-swap

is the amount of swap space on disk being used (the shortfall in RAM).

swap

is the amount of swapping (the sum of swap-in and swap-out).

swap-in

is the number of pages of memory swapped in from disk per second.

swap-out

is the number of pages of memory swapped out to disk per second.

  1. Hardware—The hardware the operating system runs on is often a bottleneck in performance. Every interrupt that is generated by hardware must be processed by the kernel. The disk drive, another slow device, must also be controlled.

page

is the amount of paging (the sum of page-in and page-out).

page-in

is the number of pages of memory read in from disk per second.

page-out

is the number of pages of memory written out to disk per second.

disk

is the number of disk accesses per second.

intr

is the number of interrupts (IRQs) per second.

  1. Network—When running on a network, there can be a quite an impact on system performance due to handling the traffic. Each packet that arrives must be handled promptly, causing hardware interrupts and kernel CPU usage.

lpkt

is the number of packets on local interfaces (same machine).

fpkt

is the total number of packets on fast network devices.

fpkt-rx

is the number of received packets on fast network devices.

fpkt-tx

is the number of transmitted packets on fast network devices.

spkt

is the total number of packets on slow network devices.

spkt-rx

is the number of received packets on slow network devices.

spkt-tx

is the number of transmitted packets on slow network devices.

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