Masters of the Linux Universe

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.

TCP dump for only port 80

2011-04-18T14:27:00.000-07:00

Here is a way to dump all tcp traffic on port 80 to and from the bond0 interface:

tcpdump -w tcpdumpPort80.pcap -i bond0 tcp port 80

If you wanted to use only the eth0 interface (more common), use this example:

tcpdump -w tcpdumpPort80.pcap -i eth0 tcp port 80

Sending files from the Linux command line

2011-04-18T14:23:00.000-07:00

Here is a quick way to e-mail yourself files from a server using mutt.

$ mutt -a tcpdumpApril182011.pcap my_name@example.com < /dev/null

Mutt is great for sending MIME encoded files.

Quickly clear out a file's contents

2011-03-07T17:02:00.000-08:00

If you ever have the need to quickly clear out the contents of a file while preserving its priviledges and creation date, use this command:

echo " " > myConfig.xml

or

echo " " > /etc/my.cnf

Grep with filenames

2010-12-01T14:38:00.000-08:00

Sometimes you want grep to tell you what files have a pattern within a directory. Here is how to do it:

grep -H JAVA_HOME=/ /usr/local/terracotta/bin/* /usr/local/terracotta/platform/bin/*

/usr/local/terracotta/bin/start-tc-server.sh:export JAVA_HOME=/usr/java/jdk1.6.0_21/
/usr/local/bin/stop-tc-server.sh:export JAVA_HOME=/usr/java/jdk1.6.0_21/
/usr/local/bin/tim-get.sh:export JAVA_HOME=/usr/java/jdk1.6.0_21/
/usr/local/platform/bin/make-boot-jar.sh:export JAVA_HOME=/usr/java/jdk1.6.0_21/

Enjoy!

Bash for loops with a series of numbers or letters

2010-11-17T15:46:00.000-08:00

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!

Bring Netflix streaming to Linux!

2010-07-22T10:55:00.000-07:00

Considering there are a host of devices (PS3, Roxee, TiVo, LG Blu-Ray players) that run Linux internally and support Netflix Streaming, it should be an easy technical transition to bring this to Linux. Sign the petition to bring Netflix streaming to Linux. I am promoting it so I can use Netflix Streaming on my MythTV server and enhance the MythTV experience with Netflix streaming.

http://www.petitiononline.com/Linflix/petition.html

Create huge files fast with dd

2010-07-16T09:15:00.000-07:00

Here is a quick way to create very large empty files without writing every byte using dd.

# dd if=/dev/zero of=largeemptyfile.img bs=1M count=1 seek=16999
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.001772 seconds, 592 MB/s
# ls -lh
total 1.1M
-rw-r--r-- 1 root root 17G Jul 16 09:07 largeemptyfile.img
# du -h
1.1M .

Notice that the actual file is only 1.1 MB, but the file shows as 17GB. This is because dd basically wrote the first and last parts of the file, and left the middle alone. You can now use this file for anything, such as a Xen disk image. Once it is in use, it will report as the full 17GB with du.

Killing zombie processes

2010-07-08T09:16:00.000-07:00

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.

New t-shirt shop

2010-07-08T08:09:00.000-07:00

I have partnered with CafePress.com to create some suave t-shirts about tech. See my shop at:

http://www.cafepress.com/Peachfuzztech

Enjoy!

Sample /etc/dhcpd.conf configuration

2010-06-24T16:18:00.000-07:00

Here is a basic dhcpd configuration.
For more info, look at /usr/share/doc/dhcp*/dhcpd.conf.sample.

ddns-update-style ad-hoc;

subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.100 192.168.1.200;
option routers 192.168.1.1 ;
option domain-name "mydomain.com" ;
option domain-name-servers 4.2.2.2 4.2.2.3 ;
}

Make a service persistant on Ubuntu

2010-06-18T15:58:00.000-07:00

The latest versions of Ubuntu (10.04 is where I noticed this behavior) ignore LSB configuration, which makes chkconfig not work for some scripts. Instead, use update-rc.d-insserv to enable a service after reboot as shown. This example enables the Samba services after a reboot.

update-rc.d-insserv nmbd defaults
update-rc.d-insserv smbd defaults

Find the PID number with nothing else

2010-06-17T15:37:00.002-07:00

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.

Write on my Linux wall

2010-05-27T11:20:00.003-07:00

To display a text message to other users logged into a *nix system, use the wall command. For example:

wall "Deploying new .ear file in five minutes."

This will send the message to all users logged into the system, whether they be physically on a console, via ssh or ftp.

Comment lines in vi

2010-01-08T09:07:00.002-08:00

If you need to comment the next 10 lines within vi, execute the command within the command mode:

:.,+10s/^/#