Capistrano with sudo

Capistrano with sudo

An easy way to execute commands with sudo from within a capistrano job is to add the prefix  #{sudo} to a command within your capistrano task.  For example:

task :make_protected_dir, :roles =>db do
  run "#{sudo} mkdir /root/mydir"
end

Another example:

task :restart_httpd, :roles =>app do
  run "#{sudo} /etc/init.d/httpd restart"
end

Then from the command line, load your file with these entries:

cap -f capfile

Then, execute the commands:

cap make_protected_dir

cap restart_httpd

More info:

https://github.com/capistrano/capistrano/wiki/2.x-DSL-Configuration-Tasks-Task

Trace your python programs

Bash programming has a very helpful command of:

bash -x myscript.sh

This will show you what bash is doing while running through myscript.sh. Python has the same functionality, through this command:

python -m trace --trace myscript.py 

Very useful in debugging python programs.  Additional info:

http://docs.python.org/library/trace.html

Make script compatible with chkconfig

To make an init script compatible with chkconfig (to autostart on next runlevel change), add the following header to your script within it's /etc/init.d/ file, for example, /etc/init.d/myscript

#!/bin/bash

#
# myscript     init script to manage myserver
#
# chkconfig: 2345 90 35
# description: A server which does amazing things.
#


Now, add it with these commands:

/bin/chmod +x  /etc/init.d/myscript
/sbin/chkconfig myscript --add
/sbin/chkconfig myscript on
/sbin/chkconfig myscript --list
myserver       0:off    1:off    2:on    3:on    4:on    5:on    6:off


Within the chkconfig definition line, 2345 means the runlevels it will be started under, and 90 35 are the start and kill priorities, an integer between 0 and 99.  In this example, it would be started as one of the last services, and killed (stopped) as one of the earlier processes.

Convert videos to iPad 2 format

Recorded programs on my MythTV are in a lossless HD mpg format, which doesn't play well on my iPad2 using AirVideo Server over wlan (via wine). So, instead of having AirVideo Server converting it through the wine abstraction layer (which requires more CPU/memory, and uses ffmpeg.exe anyway), I just run this user job from my MythTV server to convert the files that I care to watch on my iPad.

Step 1:
Create this file which I call /usr/bin/mythconverttoipad. If you have an issue with "too may threads," remove -threads 16. I am using this script on a 3 core machine, the -threads option speeds things up a bit.

#!/bin/bash
DIR=$1
FILE=$2

echo $DIR
echo $FILE

ffmpeg -y -i $DIR/$FILE -ab 320kb -vcodec libx264 -b 3200kb -s 1280x720 -threads 16 $DIR/$FILE.m4v


Step 2:
Make the script executable.

chmod +x /usr/bin/mythconverttoipad

Step 3:
Add script as user job within MythTV.

Within mythtv-setup add the following user job:

/usr/bin/mythconverttoipad %DIR% %FILE%

Step 4:
Enable it within rules.

Within a program recording rule (within mythfrontent), enable this user job to be run post-recording.

Step 5:
Access the files from Air Video client or other player.

If you have questions, please comment.

Bash for loops with a series of numbers or letters

Bash scripting is great. Here is a quick trick to funnel a series of numbers (or letters) into a variable, and thus an argument of a script:


#!/bin/bash
for a in {1..18}
do
echo "The number $a"
done


#!/bin/bash
for a in {a..z}
do
echo " The letter $a "
done

Here is another example:

for a in {0..15};  do  /usr/sbin/xm vcpu-pin 0 $a 0-1,4-15;  done


Such a quick and easy trick!

Killing zombie processes

Kill those persistent and annoying zombie processes.


ps -e -o ppid,stat | grep Z | cut -d" " -f2 | xargs kill -9

Tested on Fedora for accuracy.  

Find the PID number with nothing else

Use this combination to find a PID number without anything else in the output:

ps -ef | grep -v grep | grep ssh | cut -d" " -f3
3012

Enjoy that kungfu knife-kick combo.

Process affinity

Here is how to bind a program to a CPU (process affinity):

Bind processes to a CPU core

An example would be:

taskset -pc 0,1,2 20509

to set processid #20509 to have affinity (bind) on Cpu0, Cpu1, and Cpu2. To bind it to a single core, use the command:

taskset -pc 0 20509

to bind it to Cpu0.

Remove old files

If you don't use logrotate to remove or archive old logs, here is a way to remove old logs using the -ctime directive within the bash command find.

/usr/bin/find /var/log/tomcat -name *.tgz -ctime +15 | xargs rm -rf

Add an temporary user account

If you need an account for a set period of time, or an account that you don't want to deactivate later, add the -e option on useradd:

useradd -m -e 2009-12-01 -c "Temp Account" tempUser

This user account will expire on December 1st, 2009 and will lock the user and their password.

Grep entire directories

To find a phrase that could be found somewhere in the current directory, use the command:

grep -r -i searchString ./

For example:

grep -r -i splunk /etc

This would search the entire /etc filesystem for any line with the word "splunk" located therein. Another way to do this would be the command:

find / -type f -print | xargs grep splunk

It works well with HP-UX and other Unixes.

Reboot your computer after 4082.97902312 years

For some cool reason, the maximum time that the Linux shutdown command will accept is 2,147,483,647 minutes, which is 4082.97902312 years. If you think your hardware is going to last that long, execute the command:

#shutdown -r -F 2147483647

In a little over 4,000 years, it will reboot and check your disks. Hopefully by then you will be doing something cooler than counting down, like golfing on Mars.

Unique lines in a file

If you want to see all unique lines within a file, use the uniq command within Linux/Unix. To do so, just execute uniq against a file.

#uniq /var/log/messages

Or, less elegantly...

#cat /var/log/messages | uniq

This will also work with standard input.

Simple bash for loop

for kernelrpm in kernel-smp-2.6.9-5.EL kernel-smp-2.6.9-34.EL kernel-smp-2.6.9-67.0.1.EL kernel-utils-2.4-14.1.117

do rpm -e $kernelrpm

done