Masters of the Linux Universe

Very useful bash $PS1 setting

2014-08-12T15:26:00.003-07:00

My ~/.bashrc settings have a killer setting for how my shell prompt looks:

case $- in
*i*)
export PS1="\[$(tput bold)\]\[$(tput setaf 6)\]\t \[$(tput setaf 2)\][\[$(tput setaf 4)\]\u\[$(tput setaf 1)\]@\[$(tput setaf 4)\]\H \w \[$(tput setaf 6)\]\[$(tput setaf 2)\]]\[$(tput setaf 4)\] \$? \\$ \[$(tput sgr0)\]" ;;

*) return ;;
esac

The result:

22:19:43 [myuser@myserver.example.com ~ ] 0 $

This shows the current system time, username@server FQDN, pwd, exit code of last command, and regular user or root prompt.

This works in both interactive and non-interactive shells (hence the case statement). Enjoy. Additional info can be found here:

Bash $PS1 generator
10 Bash $PS1 examples
Bashrc generator

Ruby Regex

2014-07-09T13:45:00.003-07:00

Just wanted to pass along two very useful sites for regular expressions with Ruby

Ruby regex calculator:

http://rubular.com/

Ruby regex documentation:

http://www.tutorialspoint.com/ruby/ruby_regular_expressions.htm

MOTD on Amazon Linux

2014-04-01T16:45:00.000-07:00

Just had to pass this along, very useful.

https://coderwall.com/p/hr_9pw

Google search plugin for terminator

2013-05-22T18:26:00.002-07:00

This is going to save me 10 minutes a day. Props to the developer.

https://github.com/choffee/terminator-plugins

This is a plugin which adds a function to the context menu of terminator (my favorite Linux-based terminal emulator) which will search Google for the selected text. Before I discovered this, I would select the text, copy it to a browser like Chrome or Firefox, then searched Google. This is going to make me much more efficient.

Capistrano with sudo

2013-01-16T16:49:00.002-08:00

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

S3 Utility

2013-01-01T14:10:00.002-08:00

Here is a great tool for working with Amazon S3. It even has a wide variety of repos available (easier than compiling from source). s3cmd is very easy to setup. It is the easiest to work with of all the S3 tools I have used.

http://s3tools.org/s3cmd

Trace your python programs

2012-08-23T12:53:00.000-07:00

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

Create ssh public key from private key

2012-08-03T12:18:00.000-07:00

If you have a private key and want to create the public key from that (to put in ~/.ssh/authorized_keys, for example), do the following:

ssh-keygen -f <my_private_key> -y > <my_public_key>

For example:

ssh-keygen -f ~/.ssh/id_rsa -y > ~/.ssh/id_rsa.pub

If you are using this to ssh with keys, add my_public_key (eg. ~/.ssh/id_rsa.pub) to ~/.ssh/authorized_keys on the remote server.

Then ssh with the private key to the remote server to test.

EC2 Bundling an AMI -- Server.InternalError: An internal error has occurred

2012-05-14T15:31:00.004-07:00

Once you try to re-bundle an OS image that has been previously bundled, it will complain about /etc/ec2/amitools/cert-ec2.pem not being present. I figured that was my certificate, but it is EC2's X.509 public key certificate, not mine (docs are somewhat confusing about that). Since they were stripped out of the AMI last time it was bundled, I reinstalled the tools to restore these certs and no errors any more.

AWS API tools:

http://aws.amazon.com/developertools/368

Hope this helps.

Original EC2 forum posts:

https://forums.aws.amazon.com/thread.jspa?messageID=345021

https://forums.aws.amazon.com/message.jspa?messageID=344101

Ubuntu and EC2

2012-04-25T18:05:00.001-07:00

Great blog on the nitty gritty of working with EC2:

http://alestic.com/

Install Cisco AnyConnect on Ubuntu/Debian/Mint 64 bit

2012-03-27T18:02:00.000-07:00

Looks like there are no 64 bit Cisco AnyConect VPN Clients. Here is a workaround to get them working on a Debian-based 64 bit OS:

http://www.virtualcorner.nl/?page_id=220

Linux Mint on Gigabyte GA-Z68X-UD3H-B3

2012-03-26T14:01:00.001-07:00

I tried to install Linux Mint on a desktop with Gigabyte GA-Z68X-UD3H-B3 motherboard with its Intel raid array configured with two of three hard drives. I wanted to install Linux Mint 12 x64 on the third drive. When trying to boot, I got the error message:

udev timeout killing /sbin/modprobe -bv pci:

I had to add the grub option of nomodeset as a kernel paramater. It then was able to install from there. Here are more details:

http://forums.linuxmint.com/viewtopic.php?f=46&t=95351&p=547012#p545731

DenyHosts setup on Red Hat/Centos/Amazon AMIs

2012-02-24T14:50:00.001-08:00

This is a really useful tutorial for setting up DenyHosts to protect against brute force ssh attacks.

http://www.cyberciti.biz/faq/rhel-linux-block-ssh-dictionary-brute-force-attacks/

DenyHosts homepage:

http://denyhosts.sourceforge.net/

pv

2012-02-23T12:14:00.003-08:00

This was so good I had to repost it here. It is about a useful utility called pv which shows a progress report of running processes:

http://www.dp.cx/blog/pv--one-of-the-most-useful-applications-around.html

Make script compatible with chkconfig

2011-12-14T10:16:00.000-08:00

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.

Just kill the process

2011-11-29T13:04:00.000-08:00

/bin/kill -9 `/bin/cat /var/run/snmpd.pid`

To kill just the PID reported by the process as the active PID (with a shotgun, -9) and nothing else, use this shortcut.

sed add line at end of file

2011-11-03T12:22:00.000-07:00

If you want to add a a line of text to the end of a file, and want to do the edit in place, use this syntax:

sed -i '$ a\This is some sample text.' /foo/bar

Visual explanation of SQL joins

2011-10-31T11:38:00.000-07:00

I wish I had these pictures in my head when I started learning about joins in SQL. Might have been a DBA instead of a systems engineer.

http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html

Charge iPad or iPad2 over usb in Linux

2011-10-09T20:24:00.000-07:00

First, follow these instructions:

http://korenkov.info/ipad-ipad2-charge-ubuntu

For later versions of udev (I tested this on Ubuntu 11.04), make sure that /etc/udev/rules.d/95-ipad_charge.rules looks like the following examples.

For iPad:

ENV{DEVTYPE}=="usb_device", ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="05ac", ATTRS{idProduct}=="129a", RUN+="/usr/bin/ipad_charge"

For iPad2:

ENV{DEVTYPE}=="usb_device", ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="05ac", ATTRS{idProduct}=="129f", RUN+="/usr/bin/ipad_charge"

Then restart udev or reboot.

Lexmark z645 install redux

2011-10-05T10:49:00.000-07:00

This is the best way to install the printer driver for the Lexmark 600 or 640 series drivers on Ubuntu:

https://help.ubuntu.com/community/HardwareSupportComponentsPrinters/LexmarkPrinters

sed with variables

2011-07-25T12:32:00.000-07:00

Here is an example of how to get sed to replace values within files with variables:

for a in {1..12} ; do sed -e s/0/"$a"/g myConfig > myConfig$a ; done;

This is useful if you need to have an iterated set of config files, for instance.

In place editing of files quickly

2011-07-25T12:16:00.000-07:00

Use the sed -i option for in place editing of files:

sed -i 's/foo/bar/g' FILENAME

It will replace all occurances of foo with bar within FILENAME

Convert videos to iPad 2 format

2011-07-11T13:48:00.000-07:00

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.

Control Roku player over telnet

2011-06-07T15:10:00.000-07:00

My young boys have broken several remotes for my Roku player. I am tired of buying new ones. There is a way to control the Roku player over the network, though. Use telnet on port 8080, for example:

[root@mythtv3 ~]# telnet 192.168.1.8 8080
Trying 192.168.1.8...
Connected to 192.168.1.8.
Escape character is '^]'.
H0A0AC134945
ETHMAC 00:0d:4c:43:90:11
WIFIMAC 00:0d:4c:43:90:11
>press right
>press down
>press select

The available commands are:
press up
press down
press left
press right
press select
press home
press fwd
press back
press pause

Additional information:

http://forums.roku.com/viewtopic.php?t=20106

Install capistrano on RHEL or CentOS

2011-04-26T13:01:00.000-07:00

Capistrano is great for automating system tasks. Here is how to install it on RPM-based systems:

# yum install ruby rubygems
# gem install mocha echoe rake capistrano

Please note that mocha, echoe are optional for tests, but I included them in these instructions.