Install ffmpeg

First, we should install the ffmpeg package. The Fedora Linux does not include ffmpeg in its repository for some reasons but the RPM Fusion repository provides it for us. To install the ffmpeg package, add RPM Fusion repository first.

The install the ffmpeg package:

# yum install ffmpeg

Convert video file format with ffmpeg

The basic command to convert video file input.wmv to onput.mp4 is as follows.

# ffmpeg -i input.wmv output.mp4

Or other format (such as .mov) by:

# ffmpeg -i input.wmv output.mov

ffmpeg determines the output video’s format by its file name extersion.

Convert video file format with ffmpeg for iPod/iPhone/iPad

The files in .mp4 format can be played on Apples devices. The iPod/iPhone/iPad have specific resolution, so we need to to convert the video files to a very high resolution since the devices can only display a limited one. We use the iPod generation 2 as the example, its screen resolution is 480×320. Hence, we can only convert the video to this resolution for smaller video file size. Similarly, the bitrate can also be set accordingly. The default one of ffmpeg (200 kb/s) is too low. To improve the quality of the converted video, we can set it to a larger one.

One good configuration for me is:

# ffmpeg -i input.wmv -s 480x320 -b 1000k output.mp4

-s sets the frame size of the video. -b sets the bitrate of the video.

Convert video file format with ffmpeg for iPod/iPhone/iPad in one command

More conveniently, we can form this command to a script convert2mp4.sh:

#!/bin/bash
ffmpeg -i $1 -s 480x320 -b 1000k /tmp/$1.mp4

Each time to convert a video file video.wmv, we can simply run:

$ convert2mp4.sh video.wmv

and the converted file is /tmp/video.wmv.mp4 after the script finishes.

The slides of tutorial on ns-2 can be download from here:

Tutorial on ns-2

Install ns-2.34 on Fedora

Download the allinone package

$ wget http://downloads.sourceforge.net/project/nsnam/allinone/ns-allinone-2.34/ns-allinone-2.34.tar.gz

Uncompress the pacakge

$ tar xf ns-allinone-2.34.tar.gz

Install needed pacakges

# yum install gcc make libX11-devel libXt-devel libXmu-devel

Ns-2 requires older version of gcc. So we install gcc-34 and gcc-34-c++ for it

# yum install compat-gcc-34 compat-gcc-34-c++

Install the allinon package of ns-2. During the install process, specify the CXX compiler we use

$ cd ns-allinone-2.34
$ CXX=g++34 ./install

Configure the environmental variables for ns-2 and nam, and add the executables to the PATH so that we can use ns and nam directly.

Add to ~/.bashrc if you use bash

NS_HOME=/full/path/to/ns-allinone-2.34
PATH=$NS_HOME/bin:$NS_HOME/tcl8.4.18/unix:$NS_HOME/tk8.4.18/unix:$PATH
export PATH

or

Add to ~/.cshrc_user if you use c shell

setenv NS_HOME "/full/path/to/ns-allinone-2.34"
setenv PATH "${PATH}:${NS_HOME}/bin:${NS_HOME}/tcl8.4.18/unix:${NS_HOME}/tk8.4.18/unix"
setenv LD_LIBRARY_PATH "${NS_HOME}/otcl-1.13:${NS_HOME}/ns-2.34/lib:/usr/local/lib"
setenv TCL_LIBRARY "${NS_HOME}/tcl8.4.18/library"

The installation is done by this step. Open another shell and try our installation:

$ nam

and

$ ns

Install ns-3.12.1 on Fedora

Install needed packages

# yum install libxml2 libxml2-devel gcc gcc-c++ make automake \
autoconf binutils openssh-server openssh-clients openssl python \
python-devel mercurial bzr scons flex bison tcpdump valgrind gdb

Download the allinone pacakge for ns-3

$ mkdir tarballs
$ cd tarballs
$ wget http://www.nsnam.org/release/ns-allinone-3.12.1.tar.bz2
$ tar xjf ns-allinone-3.12.1.tar.bz2

Build ns-3

$ cd ns-allinone-3.12.1/
$ ./build.py

We will now interact directly with Waf in the ns-3.12.1 directory

$ cd ns-3.12.1

Configuration with Waf

$ ./waf -d optimized configure --enable-examples; ./waf

Validate our installation by running one example

$ ./waf shell
$ cd build/optimized/examples/
$ udp/udp-echo

Use tcpdump to display the simulation result

$ tcpdump -tt -r udp-echo-0-1.pcap

In this post, we introduce how to set up keys for git, how to configure non-standard SSH port for git, and how to use the first git repository.

Users’ SSH private/public key pairs

Every user of git, administrator or a normal user, need to have a private/public SSH key pairs in ~/.ssh.

New users need to generate the key pairs (if they don’t have one) by executing this command:

$ ssh-keygen -t rsa

After generating the key pairs, the user can give the public key (~/.ssh/id_rsa.pub) to the git server administrator and ask he/she to create a account and repository.

After the git server administrator adds the new user by its public key to the git server, the user can starts to use git.

Non-standard SSH port

This section only for the git servers that use non-stardard SSH port, i.e. other than 22.

If sshd is listening on non-standard port(s) on the git server, for example 22111, the user should set SSH to use the special port. We use example.org:22111 as the example here.

Put these two lines in your ~/.ssh/config file:

Host example.org
  Port 22111

If this ~/.ssh/config file doesn’t exist, you should create it first and set it’s mod to 744:

$ chmod 744 ~/.ssh/config

Create the new repository

This section only for users to create new repository. If the user is to use an already exist repository, please skip this section. Besides, the steps in this section only need to be done once for one repository.

We use the example that the administrator create repository repo1 for user1 and give user1 write privilege to this repository. We assume the address for this repository is git@example.org:repo1.git . Now we introduce how does user1 create the new repository repo1.

As user1 has the write privilege on the repo1 repository, it can create this repository on it’s local machine first and then push it to the git server. After pushing it to the git server.

These operations are done by user1 on its local machine:

$ mkdir repo1
$ cd repo1
$ git init
$ touch README
$ git add README
$ git commit -a -m 'first commit'
$ git remote add origin git@example.org:repo1.git
$ git push origin master

If it successes, the new repository is created on the git server.

Use the repository

Please note that step 1 only need to be done for the first time. After getting the repository to a local directory on the user’s local machine, the user only need to follow step 2 to step 5.

1. Clone the repository for the first-time. You only need to do it once for the first time, for the later usage of this repository, you continue use this local directory.

$ git clone git@example.org:repo1.git

A directory named repo1 will be created in the current directory.

If you want to use the repository directory in the previous section, just add these line to the end of .git/config:

[branch "master"]
remote = origin
merge = refs/heads/master

2. Pull the updates made before by you or the others. Use “git pull” command in the repository’s directory.

$ cd repo1
$ git pull

Then you can work on this updated copy of the repository by editing the files.

If you add a file or directory (for example, add directory a/b and file a/t.txt), you can add it to the repository by:

$ git add a/b a/t.txt

3. Commit the changes made by you with a message

$ git commit -a -m 'update the files'

4. Push it to the git server

$ git push

By now, your changes have been pushed to the git server. When the others use “git pull” command, they will get the new version of the source codes that have changed by you.

You can use “git log” to see the logs of all the commits of this repository.

You may be also interested in more git solutions.

64-bit flash plugin for Firefox on Linux

First, download Flash Player Release for 64-bit Linux from Adobe Labs.

Then, unpack the package:

$ tar xf flashplayer.tar.gz

Check whether all needed library is ready for it. If not, install the needed packages.

$ ldd libflashplayer.so

Give it executable attribute:

$ chmod +x libflashplayer.so

Copy the plugin to the plugin directory so that Firefox can use it:

$ cp libflashplayer.so ~/.mozilla/plugins/

32-bit flash plugin for Firefox on Linux

32-bit flash plugin can also work well for 64-bit firefox on 64-bit Linux. We can use the rpm packages from adobe’s repository.

First, install adobe release repository:

# rpm -Uvh http://linuxdownload.adobe.com/adobe-release/adobe-release-i386-1.0-1.noarch.rpm

Install nspluginwrapper so that 32-bit plugins can run on 64-bit system, and 32-bit alsa plugin for pulseaudio so that the 32-bit flash plugin can play sound on the 64-bit system.

# yum install nspluginwrapper.{x86_64,i686} \
 alsa-plugins-pulseaudio.i686 --disablerepo=adobe-linux-i386

Install the 32-bit flash plugin:

# su -c 'yum install flash-plugin'

Install the “External Editor” Thunderbird extension

Download the “External Editor” plugin.

And install it to Thunderbird.

Configure the external editor

Option 1: use gvim

This is an easy method which use gvim.

In External Editor’s Preference, set the Text Editor to:

gvim -f

Option 2: use vim in gnome-terminal

If you prefer to use vim in a terminal as me, you may consider this option. Setting vim in the editor will simply fail. We may use ‘xterm -e vim’ as the editor, but xterm looks ugly in a modern computer compared to shells like gnome-terminal. However, we need a little trick to use vim inside gnome-terminal.

First, create a script “callvim”:

#!/bin/bash

gnome-terminal --geometry=80x40 --disable-factory -e "vim $*"

Save it to a directory in your $PATH, such as ~/bin/, and remember to give it executable by ‘chmod +x callvim’.

Then, set the Text Editor in External Editor’s Preference to

callvim

How to use it

When creating or editing email, invoke vim to edit it by the keyboard shortcut Ctrl+E.

Edit the email in Vim and save and exit. The email in Thunderbird’s editor is changed.

Customize Vim for editing email

We can customize Vim to be a better email editor by set email-specific configuration in ~/.vimrc. Below is my configuration in .vimrc which set the text width to 68 charactors, set automatic spell check, default file encoding to be iso8859-1 and utf-8. Abbreviation is also available, which may be frequently used in writing email.

My email configuration in ~/.vimrc

au FileType mail call FT_mail()

function FT_mail()
    set nocindent
    set noautoindent
    set textwidth=68
    " reformat for 72 char lines
    " normal gggqGgg
    " settings
    setlocal spell spelllang=en
    " setlocal fileencoding=iso8859-1,utf-8
    set fileencodings=iso8859-1,utf-8
    " abbreviations
    iabbr  gd Good Day!
endfunction

SSH

Software: PuTTY

Direct download: PuTTY

SCP and SFTP

Software: WinSCP

Direct download: WinSCP

VNC viewer

Software: TightVNC

Direct download: TightVNC

Another option is the free RealVNC free client (not open source) which can pass the special keys (such as Alt+Tab) to the server : download RealVNC viewer.

On Mac OSX, you may consider the Chicken VNC client.

Please read [1] for requirement when using Spirit. Currently, the version of iTunes used should be iTune 9 earlier than 9.2. The firmware’s version should be 3.1.2, 3.1.3 or 3.2.

My iPod which I use in this tutorial is: iPod touch 8G 3.1.3(7E18) Model (MC086ZP). The Linux I used is Fedora 12.

Okay, let’s go!

1. Synchronise with iTunes

As what we usually do. This step is highly recommended by Spirit.

2. Dowload Spirit jaibreak for Linux and compile it

Get the source code

$ git clone http://github.com/posixninja/spirit-linux.git

Install depended development packages

$ sudo yum install libplist-devel libimobiledevice-devel

You may need to install other development packages such as make, gcc etc.

Build spirit

$ cd spirit-linux
$ make

3. Set iPod to not Auto-lock

In Settings->General->Auto-lock, select never.

4. Connect iPod touch to the Linux box with cable

5. jailbreak it

$ ./spirit

6. iPod will reboot

The jailbreak work will start. Wait for a few minutes.

7. Done

Congratulations! Now, look for the Cydia icon. My favourite applications are Terminal and OpenSSH. Remember to change the password of root and mobile users for security.

Reference:

[1] http://www.spiritjb.com/

1. Pipe-lining network connection

Most of us use a broad band width network, then why not pip line the connection from Firefox?

Type “about:config” into the address line and enter.

Set “network.http.pipelining” to “true”
Set “network.http.proxy.pipelining” to “true”
Set “network.http.proxy.pipelining.ssl” to “true”
Set “network.http.pipelining.maxrequests” to some number like 25. This number means how many requests Firefox can make at most. It depends on the network. I am a crazy guy and I set it to 50 in my browser.

2. No waiting before action

Type “about:config” into the address line and enter.

Right-click on the page and select New-> Integer.
Name it “nglayout.initialpaint.delay” and set its value to “0″. This value is the amount of time the browser waits before it acts on information it receives.

3. Put cache into memory

If your memory is larger than 1GB, you can try this method. If you experience problem, please change it back. (delete browser.cache.disk.parent_directory)

Type “about:config” into the address line and enter.

Right-click on the page and select New-> String.

Name it “browser.cache.disk.parent_directory” and set its value to “/dev/shm/ffcache“. The Cache of Firefox will be putinto /dev/shm/ffcache/Cache.

4. Diable IPv6 support

If you experience very slow DNS lookup in Firefox, you can try to disable IPv6 support in Firefox and Linux if you don’t use it:

For Firefox:

Type “about:config” into the address line and enter.
Set “network.dns.disableIPv6″ to “true”

For Linux:

I test it on Fedora 12. On other systems, the configuration may be different.

# cp /etc/modprobe.d/dist.conf /tmp/dist.conf.bak0
# echo “alias net-pf-10 off” >> /etc/modprobe.d/dist.conf
# echo “alias ipv6 off” >> /etc/modprobe.d/dist.conf

Then restart you Firefox and try whether Firefox is faster and enjoy it :)

Generate SSH key pair

If you do not have a SSH private/public key pair, let’s generate one first.

$ ssh-keygen -t rsa

By default on Linux, the key pair is stored in ~/.ssh (id_rsa and id_rsa.pub for private and public key).

Copy public SSH key to the remote machine

The easiest way

Let ssh-copy-id do it automatically:

$ ssh-copy-id username@remotemachine

The manual way

Copy the public SSH key to remote machine

$ scp .ssh/id_rsa.pub username@remotemachine:/tmp/

Log on the remote machine

$ ssh username@remotemachine

Append your public SSH key to ~/.ssh/authorized_keys

$ cp ~/.ssh/authorized_keys ~/.ssh/authorized_keys.bak   # backing up before changing is a good habit
$ cat /dev/shm/id_rsa.pub >> ~/.ssh/authorized_keys     # append pub key to authorized keys list

Make sure the mode of ~/.ssh/authorized_keys is 755:

$ chmod 755 ~/.ssh/authorized_keys

Possible Problems

Home directory permission

Check the home directory’s permission which may cause the key-based login fail (suppose the home directory is /home/zma):

# chmod 700 /home/zma/

Update history
Add setting of authorized_keys’ mode setting.
Aug. 31, 2011. Revise writing.