Raspberry Pi Swap Space

-
Who took my slice of pi?  

Sometimes I ask myself that while looking in the fridge. This time, I am looking at the top command and see nearly a quarter of the reserved swap space in use.  The question is purely academic, and spurred by curiosity, I wrote a bash script to learn the answer.

The script, swapid, searches through the process list, identifies the process name and amount of swap used, and then sorts the output by swap size. 

With Linux, processes can be viewed and interrogated like a file system. Run

$ ls /proc

and you'll see it sprinkled with subdirectories named with numbers. These numbers correspond to process ids. Inside each of these subdirectories is a file named status, and running

 $ cat status

reveals a bunch of process information.

At this point, it's simply a matter of using awk and grep to pick out the attributes of interest; in this case, "Name" and "VmSwap."

Output is written to the /tmp directory, sorted, printed to the console, and then deleted. 

Source code for swapid

#!/bin/bash
tmpfile="/tmp/swapid.tmp"
if [ -f $tmpfile ]; then rm $tmpfile; fi
for f in /proc/*/status
do
    name=$(grep ^Name $f)
    swap=$(grep ^VmSwap $f)
    echo $name" "$swap | awk '{print $2" "$4" "$5}' | 
        grep -i kb | grep -v grep >> $tmpfile
done
sort -n -k 2.1 $tmpfile
rm $tmpfile

After typing this in using your favorite editor, it helps to make the script executable:

$ chmod +x swapid

Running the script, the last dozen output lines show the largest slices of swap space goes to process php-cgi:

$ ./swapid
. . .
smbd-notifyd 1560 kB
lpqd 1564 kB
php-cgi 1784 kB
php-cgi 1792 kB
php-cgi 1800 kB
php-cgi 1812 kB
php-cgi 2040 kB
php-cgi 2684 kB
php-cgi 2684 kB
php-cgi 2684 kB
php-cgi 2684 kB
php-cgi 2684 kB

So now I have the answer to the question above: the apache2 server took it! And 10 slices to boot!

Comments

Post a Comment

Popular posts from this blog

MR2 Check Engine

-
Image
Shown here is the 1991 Toyota MR2. Thanks to the mechanical skills of a family enthusiast, it purrs, growls, and turbo whistles like a dream.   My hardware ability doesn't go much further than oil changes. Rather, my expertise is in software, and I wrote an Android App (iOS version is in progress) to diagnose the flashes of the check engine light. This second generation MR2 predates the OBD2 connector, a standard used to diagnose engine, transmission, and emissions problems quickly and easily. Instead, we have a flashing check engine light which needs some deciphering, followed by a lookup in the service manual. Basically, you count flashes to arrive at fault code number. A short pause (~1.5 seconds) indicates the start of the next digit. A medium pause (~2.5 seconds) indicates start of the next fault code. And a long pause (~4.5 seconds) means the sequence has ended and will repeat. The video below corresponds to the codes 41 and 51. Using the the MR2 Check app and selecting the 3
Read more

Bookshelf: UNIX A History and a Memoir

-
Image
  A man page will give you, in black and white, specific information about UNIX. Brian Kernighan's new book adds color and depth about UNIX you won't find anywhere else. I'm not a gray beard (yet), but I imagine they would plow through the book knowingly, but at the same time, learn a few things. Those new to UNIX -- recent college grads or those experimenting with Raspberry Pi -- would be better off starting with Chapter 8 which describes more relatable events and the descendants of UNIX, including Minux and Linux. It's when they start to ask questions like "Where does UNIX come from?" and "Why is Gamora grep?" that they should start from the beginning: Bell Labs, 1969. Kernighan opens with a birds-eye-view of Murray Hill New Jersey, zooms in on the buildings, the offices, the significance of Center 1127, and offers a brief look at some of the key players there. As I progressed through the book, the two factors that made UNIX not just possible, bu
Read more

Bookshelf Classic: The C Programming Language

-
Image
My first job had me programming in Microsoft BASIC for the IBM PC (DOS).  BASIC worked well enough, but its limitations were clear.  The language was interpreted and therefore slow.  More importantly, it wasn't a modern structured language, and instead, relied on line numbers and the GOTO statement.  Anyone who has read Dijkstra knew  GOTO was a bad thing . Having learned a structured language in college ( PL/I ), using BASIC felt unnatural.  When a C compiler became available for the PC, I saw a chance to improve and modernize our software.  The problem was selling the idea -- a problem made harder because I wasn't fluent in C. "It would be a staffing problem.  Not many people know C, but we can find a lot of programmers who know BASIC," noted one manager. The argument was strong as my knowledge of C was weak.  But I knew that C, by design, was a small language and thus easy to learn.  "It has about 30 keywords," I proffered to another manager. U
Read more