If you ever wanted to check how many threads a particular process spawned off in Linux, you can use
Inspired by a G+ post by Thomas Weeks .
swap memory is something used by the OS to essentially swap data to and forth if the main memory is not available. It is several times slower than RAM, since it uses hard disk to store the memory. And if you are constantly swapping, your system performance is going to be impacted quite a lot. You should always ensure that your system is not swapping by adding the required RAM and/or stopping your application(s) from using so much memory. At times, because of spike in utilization, the OS might briefly use swap. And when it does, it doesn’t release the memory from swap. So from an analysis prospective, it makes it difficult to check (quickly) if your system is using swap or not. This is similar to errors on an interface in a router. Unless you clear them and monitor, you don’t know when the errors happened.
I was not aware that you could turn off swap devices while the OS is running and then enable them again. So here are the commands to do that in Linux
[code]swapoff -a[/code]
This essentially disables swap on all devices configured for swap in /etc/fstab
[code]swapon -a[/code]
This does the opposite of the first command. Enabled swap on all devices that have swap configured.
Tom put this into a nice alias by doing the following
[code]alias unswap=’sudo swapoff -a && sudo swapon -a'[/code]
Thx Tom…
I like shiny new toys :). Even though perl is pretty powerful and more than enough for the simple tasks I get to automate from time to time, I want to start learning python and find out first hand, why the whole geek community is raving about it.
As I start to write new scripts in python, I wanted to document how I used to do some things in perl and how I implemented them in python.
One of the standard features of any script I write is to “clear” the screen before starting to send output to the console. Here is the comparison between perl and python
[code]system $^O eq ‘MSWin32’ ? ‘cls’ : ‘clear’; [/code]
[code]
# Clear screen, based on the OS
if (os.name == ‘nt’):
os.system("cls")
else:
os.system("clear")
[/code]
Here is the first update on Project Uptime. I spun up a new server (doesn’t that sound so odd.. spun up a new server!! :)) with 512MB of RAM running Ubuntu 11.1o (Oneiric Ocelot). First order of business after spinning up the server?
[code] sudo apt-get update [/code]
[code] uname -r [/code]
[code] apt-cache search linux-image [/code]
[code] sudo apt-get install linux-image-LATEST-VERSION [/code]
[code] sudo init 6 [/code]
Quick note for self. Simple bash loop to find out the size of each directory in the existing directory. This script is useful if you are running our of disk space and want to quickly find out the offending directory.
[code]for dir in $(find ./ -maxdepth 1 -type d); do echo ${dir}; du -ch ${dir} | grep -i total; done [/code]
Breaking this down
The uptime of this blog has been really bad recently. I switched to hosting it on a Rackspace virtual server last year and went with the cheapest option. A 256MB Linux virtual server that was costing me ~$12/month. I never got around to tuning the OS, so the server was always using swap and would go down pretty much every day. Last week, I upgraded the plan and moved to a 512MB server. But the uptime hasn’t been any better. Here’s a report from Pingdom (which by the way is a great service to track the uptime and responsiveness of your website) showing the availability of the site over the last year 
96%!!.. And for someone that has been working in the operations and infrastructure world, that is unacceptable :). So my new goal is to maintain at least 99.5% uptime. Here is my plan to achieve this
I plan to blog the progress and learnings as I implement this plan.
There are tons of sites (and tons of different ways to do this) about this information.. But wanted to note this down for my personal records. If you ever wanted to search for and replace certain text in a file, you can do it with perl with this quick one liner
[code]perl -p -i -e ‘s/ORIGINAL_STRING/NEW_STRING/g’ FILE_NAME [/code]
Say you want to find out how many hits you are getting t0 a specific page from a particular source IP, you can use this quick collection of Linux tools to get this data
[code]grep -i "URL_TO_CHECK" PATH_TO_APACHE_ACCESS_LOG | cut -d’ ‘ -f 1 -| sort |uniq -c | sort -rn > ~/ip_report.txt[/code]
You are using
Example :
[code]grep -i "GET /" /opt/apache/logs/access_log | cut -d’ ‘ -f 1 -| sort |uniq -c | sort -rn > ~/ip_report.txt[/code]
gets you the report of hits to the index page.
I ran across a video of Peter Hurley, as a guest post on Scott Kelby’s blog, in which he discusses the importance of positioning the jaw lines of your subjects when taking portraits. Sri stopped by to check on Virat yesterday along with his family and I thought I should try out this tip. The effect was amazing.
BEFORE (as I would normally take portraits) 
AFTER (Shebang!!) 🙂 
Quick howto on finding the list of files being accessed by a process in Linux. I needed to find this for troubleshooting an issue where a particular process was using an abnormally high percentage of CPU. I wanted to find out what this particular process was doing and accessing.
For example, if I wanted to find the list of files being accessed by mysql, the process would look as such
[code] ps -ef | grep mysqld [/code]
which would show the output as
[code]samurai@samurai:~$ ps -ef | grep mysqld
mysql 3304 1 0 Feb04 ? 00:00:23 /usr/sbin/mysqld
samurai 23389 23374 0 14:57 pts/0 00:00:00 grep –color=auto mysqld
[/code]
I can then find the list of files being used by mysql by running
[code] sudo ls -l /proc/3304/fd [/code]
which would give me
[code]
lrwx—— 1 root root 64 Feb 7 15:00 0 -> /dev/null
lrwx—— 1 root root 64 Feb 7 15:00 1 -> /var/log/mysql/error.log
lrwx—— 1 root root 64 Feb 7 15:00 10 -> socket:[4958]
lrwx—— 1 root root 64 Feb 7 15:00 11 -> /tmp/ibdu9WRh (deleted)
lrwx—— 1 root root 64 Feb 7 15:00 12 -> socket:[4959]
lrwx—— 1 root root 64 Feb 7 15:00 14 -> /var/lib/mysql/blog/wp_term_relatio nships.MYI
lrwx—— 1 root root 64 Feb 7 15:00 15 -> /var/lib/mysql/blog/wp_postmeta.MYI
lrwx—— 1 root root 64 Feb 7 15:00 17 -> /var/lib/mysql/blog/wp_term_relatio nships.MYD
lrwx—— 1 root root 64 Feb 7 15:00 18 -> /var/lib/mysql/blog/wp_term_taxonom y.MYI
lrwx—— 1 root root 64 Feb 7 15:00 2 -> /var/log/mysql/error.log
lrwx—— 1 root root 64 Feb 7 15:00 20 -> /var/lib/mysql/blog/wp_postmeta.MYD
lrwx—— 1 root root 64 Feb 7 15:00 21 -> /var/lib/mysql/blog/wp_term_taxonom y.MYD
lrwx—— 1 root root 64 Feb 7 15:00 22 -> /var/lib/mysql/blog/wp_terms.MYI
lrwx—— 1 root root 64 Feb 7 15:00 23 -> /var/lib/mysql/blog/wp_terms.MYD
lrwx—— 1 root root 64 Feb 7 15:00 3 -> /var/lib/mysql/ibdata1
lrwx—— 1 root root 64 Feb 7 15:00 4 -> /tmp/ibvANyz7 (deleted)
lrwx—— 1 root root 64 Feb 7 15:00 5 -> /tmp/ibonS0mU (deleted)
lrwx—— 1 root root 64 Feb 7 15:00 6 -> /tmp/ibcKctaH (deleted)
lrwx—— 1 root root 64 Feb 7 15:00 7 -> /tmp/ibB5DS5t (deleted)
lrwx—— 1 root root 64 Feb 7 15:00 8 -> /var/lib/mysql/ib_logfile0
lrwx—— 1 root root 64 Feb 7 15:00 9 -> /var/lib/mysql/ib_logfile1
[/code]
