LinuxNut.org

umask

Bryce — Fri, 21 Aug 2009 13:59:16 +0000

umask determines what permissions any new files or directories will have by default. Like file permissions, it historically takes an octal value (e.g. ‘umask 002′), but can also symbolic values (e.g. ‘umask a=rx,ug+w’). I’m going to just focus on the octal values.

The octal value appears to have a lower than what you’d normally set with chmod, but this is because it is actually subtracted from the maximum possible file (666) or directory (777) permissions.

For example if you create a new directory with umask set to 022, the resulting permissions are set to 755, since 777 – 022 = 755.

Most of the time umask is set sensibly from the beginning, and you don’t have to worry about it. If you do need to change it, you’ll probably find it being set in one of your login scripts – ‘/etc/profile’ or ‘~/.bashrc’.

For more information just check the man page.

Programmer Jokes

Bryce — Wed, 19 Aug 2009 18:48:33 +0000

Here’s a bunch of programmer jokes – http://stackoverflow.com/questions/234075/what-is-your-best-programmer-joke

Unix time

Bryce — Sun, 16 Aug 2009 16:23:10 +0000

If you should happen to need to know the current time as a unix timestamp, try http://www.unixtime.se/. Alternatively typing

date +%s

at a convenient command line might be faster, and more accurate…

What distro version am I running?

Bryce — Tue, 13 Jan 2009 19:35:30 +0000

With any Linux Standard Base compliant distro (Mandriva, openSUSE, Red Hat, Ubuntu, etc…), there is an easy way to find its version number, and code name.

Just run the following command:

lsb_release -a

This should give a result such as the following:

Distributor ID:	Ubuntu
Description:	Ubuntu 8.10
Release:	8.10
Codename:	intrepid

Additionally, to find out what type of architecture your kernel is currently compiled for, just run:

uname -m

Which will give something like this:

x86_64

FFmpeg

Bryce — Sun, 11 Jan 2009 15:23:53 +0000

FFmpeg is an open-source command line utility for performing audio/video file conversions. It can be used to simply convert straight from one video format to another, or to crop, pad, rescale, change bit-rates, merge or split out audio and video, and so on…

The projects website is at http://ffmpeg.mplayerhq.hu/. Here’s a few links to some of the most useful parts of the project’s own documentation:

The simplest command format is ‘ffmpeg -i inputFile outputFile’, but it can be made as complex as required, in order to specify every single parameter of the conversion process.

To obtain the encoding details from an existing audio or video file, just run the command with only an input file specified, e.g.: ffmpeg -i somefile.avi

I’ll now list some commonly used parameters. These may do exactly what you need first time, but don’t be surprised if you have to tweak the parameters slightly for them to work on your system, with your files:

Convert AVI video to MPEG:

ffmpeg -i inputFile.avi outputFile.mpg

Convert MPEG video to AVI:

ffmpeg -i inputFile.mpg outputFile.avi

Convert FLV to MPEG:

ffmpeg -i inputFile.flv -ab 56k -ar 22050 -b 500k -s 320x240 outputFile.mpg

Audio bit-rate: 56kbps

Audio sampling frequency: 22050Hz

Video bit-rate: 500kbps

Video size: 320 x 240

Convert MPEG or AVI to FLV:

ffmpeg -i inputFile.avi -acodec mp3 -ar 22050 -f flv outputFile.flv

Audio sampling frequency: 22050Hz

Convert AVI to MPEG-2 for DVD
Note that you will probably need to change the ‘target’ and ‘aspect’ to match your needs:

ffmpeg -i inputFile.avi -target pal-dvd -aspect 16:9 outputFile.mpg

Convert sequence of JPEGs to MPEG:
Note that the image files in this example would named ‘pic-001.jpg, pic-002.jpg, etc…

ffmpeg -f image2 -i pic-%d.jpg outputFile.mpg

Convert MPEG or AVI to sequence of JPEGs:

ffmpeg -i inputFile.mpg pic-%d.jpg

Convert MPEG or AVI to time-lapsed sequence of JPEGs, one per second:

ffmpeg -i inputFile.mpg -r 1 pic-%d.jpg

Video frame-rate: 1fps

Convert MPEG or AVI to animated GIF:

ffmpeg -i inputFile.avi outputFile.gif

Convert MP3 to WAV:

ffmpeg -i inputFile.mp3 outputFile.wav

Convert WAV to MP3:

ffmpeg -i inputFile.wav -ab 256k outputFile.mp3

Audio bit-rate: 256kbps

Remove the audio from MPEG or AVI:

ffmpeg -i inputFile.avi -an outputFile.avi

Remove video from MPEG or AVI, and convert to MP3:

ffmpeg -i inputFile.avi -an -ab 256k outputFile.mp3

Audio bit-rate: 256kbps

Add audio and video together, and convert to MPEG:

ffmpeg -i audioFile.wav -i videoFile.avi outputFile.mpg

watch

Bryce — Sun, 04 Jan 2009 14:56:41 +0000

I only came across this command fairly recently. It’s a simple command, but immensely useful.

The watch command is used to run a given command at a predefined interval, and to monitor the output in real-time until the watch command is terminated. When run, it initially only displays the first output of the given command, and then only updates it if something in the output changes.

For example to have a constantly up-to-date listing of a directory, just run

watch ls

Or similarly to have a list of who is logged onto your system, just run

watch who

These two examples are very simple, but they can be made as complex as you like.

A number of options can be used:

‘-d’ or ‘–differences’ will briefly highlight what has changed in the output
‘–cumulative’ will make the differences remain displayed
‘-n seconds‘ or ‘–interval=seconds‘ will allow the interval between program runs to be set to something other than it default of two seconds

Finally – A 64-bit version of Adobe Flash Player for Linux

Bryce — Mon, 17 Nov 2008 22:41:02 +0000

It seems to have been a long time coming, but finally an alpha version has been released. Although it’s an alpha, it’s still a vast improvement over the 32-bit version which I’ve used up until now with the aid of NPS Wrapper.

Because it can now running natively on a 64-bit architecture without the aid of a wrapper, it has a smaller memory footprint and is vastly more stable. With the 32-bit version I usually had to restart Firefox at least once a day to free up some RAM, or just to get Flash Player working again.

To get your copy, just go to http://labs.adobe.com/downloads/flashplayer10.html

GNU/Linux Distro Timeline

Bryce — Wed, 27 Aug 2008 19:48:32 +0000

Andreas has produced a cladogram (tree diagram) showing the timeline and relationship of probably every known Linux distribution. You can see the latest version of the diagram (v7.6) here, or visit the homepage http://futurist.se/gldt/.

Linux Outlaws Podcast

Bryce — Tue, 26 Aug 2008 19:10:29 +0000

Linux Outlaws is a weekly podcast, primarily about Linux, but also covering other open source goodness. The hosts of the show are Fabian Scherschel in Germany, and Dan Lynch in the UK. The show is presented in a humorous, laid-back manner, and fills the gap left after the demise of LUG Radio.

Remotely shutdown a Windows PC from Linux

Bryce — Mon, 25 Aug 2008 10:35:12 +0000

A remote Windows PC can easily be shutdown, assuming you have Samba installed on your Linux box, and you have a user account on the Windows PC that has the necessary rights.

Just enter the following command, where ‘thehostname’ is the hostname of the remote PC, and ‘theusername’ is a valid user account on the remote PC:

net rpc shutdown -S thehostname -U theusername

If the hostname is not known, or cannot be resolved, then use the following instead, where ‘123.123.123.123′ is the IP address of the remote PC:

net rpc shutdown -I 123.123.123.123 -U theusername

For more information on the command, just enter the following:

net help shutdown

Additionally, the parameters that can be used with Windows’ own shutdown command such as ‘-f’ to force or ‘-t’ to set a timeout, can also be applied to the net rpc shutdown command as well. For example the following will wait 60 seconds, and then force all running programs to terminate before shutting down:

net rpc shutdown -S thehostname -U theusername -f -t 60