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.

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:

• Supported file, image, video and audio formats
• Video options
• Audio options

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

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

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

As root, simply enter the following command, where ‘cd1.iso’ is the name of the ISO image file, and ‘/mnt/cd’ is an existing directory:

mount -o loop cd1.iso /mnt/cd

iperf -s

and the other as the client

iperf -c <Server IP>

then after 10 seconds you’ll have your result.

------------------------------------------------------------
Client connecting to 192.168.1.11, TCP port 5001
TCP window size: 8.00 KByte (default)
------------------------------------------------------------
[1912] local 192.168.1.21 port 1107 connected with 192.168.1.11 port 5001
[ ID] Interval       Transfer     Bandwidth
[1912]  0.0-10.0 sec  26.7 MBytes  22.4 Mbits/sec

Iperf is readily available as a binary for various operating systems, i.e.: Linux, FreeBSD MacOS, Windows, etc. The source code is also available.

For more information, or to download it, please visit the project’s homepage at http://dast.nlanr.net/Projects/Iperf/

The fuser command can also be used to kill the processes as well, just by adding the ‘-k’ option (e.g. ‘fuser -km /home’).