Replace your ~/.vnc/xstartup file with the following content:
#!/bin/sh unset SESSION_MANAGER exec /etc/X11/xinit/xinitrc[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup [ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources xsetroot -solid grey vncconfig -iconic & xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" & startxfce4
If you are going for a complete reinstall of OS and you need to get a list of packages you have at present, so that you can reinstall them after you have installed Linux from scratch, run the following:
#!/bin/bash
sudo dpkg --get-selections | awk '{ ORS=" "; print $1; }' > packagelist.txt
This saves the everything to packagelist.txt. Mind blown!
Here’s a quick chart I made for quick look-up for conversion between Celsius and Fahrenheit scale.
[°C] = 5/9 × ([°F] – 32)
A graphical look-up for conversion between Fahrenheit and Celsius (click to view full size)
The bold marking are at multiples of 100 degree Celsius.
As a prank project we installed a webcam at the front desk of the our office suite, and plugged it into a Linux machine. Then we had a decommissioned 14 inch monitor face the person who was just walking in so that he/she could see themselves in the monitor with absolute clarity. The text beneath said “Smile for the camera”.
This was an one line implementation with VLC. The terminal command for this would be:
vlc --sub-filter "marq{marquee=\$t \$\smile for the camera,color=16776960,position=8}" v4l2:////dev/video0
A false sense of security with some false video surveillance. Of course you can save the stream and turn it into real surveillance.
Sluggishness on your system running Linux can be caused by numerous factors – among them is a process called gvfsd-metadata.
From what I’ve heard other people say, its caused by fragmentation – possibly due to a partition that’s nearly full.
All you can do is terminate the process or delete the script from your ~/ folder.
rm -rf ~/.local/share/gvfs-metadata
Every now and then its a good idea to make sure that your home folder is not filled up past 90% or so.
To monitor the instantaneous network usage, execute the ifstat command in bash. You may need to acquire it from a repository if you don’t have it already.
sudo apt-get install ifstat
To display usage on eth0, with a 5 second delay, just once:
ifstat -i eth0 5 1
You can change the number of seconds, and the number of times you want the output displayed. If you don’t specify the count, it will go on forever until you ctrl-c out of it.
So here is a script that displays the download rates in MB/s and upload rates in KB/s every 5 seconds until you hit ctrl-c.
while : do # Press ctrl-c to exit x=`ifstat -i eth0 5 1 | tail -1 | tr '\t' ' '`; #tail -1 takes the DL and UL speeds in KB/S x1=`echo $x | cut -d ' ' -f1`; x2=`echo $x | cut -d ' ' -f2`; x1=$(echo "scale=3; $x1/1024" | bc); # Convert DL rate to MB/S printf "D: %0.3f MB/s\t U: %0.3f KB/s\n" "$x1" "$x2" done
One mild inconvenience while using Linux Mint is the default Google search in Firefox search bar. The plain ol’ google search is reformatted, and wrapped within a Linux Mint flavoured wrapper. Its not the end of the world – you can always go to google.com and then search the same word or phrase. However, many people have gotten into the habit of performing their search using the search bar on top left corner within Firefox. Getting a Linux Mint wrapper around just doesn’t look right.
Someone figured out that the google.xml file used in the search plugin was modified in the Mint distribution to create give the modified results. In order to get the original google results, just type in the following command lines:
cd /usr/share/linuxmint/common/artwork/firefox/ sudo wget http://mxr.mozilla.org/firefox/source/browser/locales/en-US/searchplugins/google.xml?raw=1 -O google.xml.fixed sudo mv google.xml google.xml.orig sudo mv google.xml.fixed google.xml sudo cp google.xml /usr/lib/firefox-addons/searchplugins/en-US/google.xml
Restarting Firefox (maybe a few times) is required to get the google results in the plain old familiar format.
The above code was obtained from: Change Back Google Search in Linux Mint
The newer releases of Ubuntu and Linux Mint have started getting stuck during LiveCD installation or after distribution/kernel upgrade. Usually the point where it gets stagnant is when it reaches this line:
kernel_thread_helper+0x7/0x10Nothing happens past that point. A solution or a workaround to this is to insert the nolapic acpi=off switch in the grub boot line. There are 3 ways to do this:
1: If you are starting a fresh install from a CD and the installation pauses at the kernel_thread_helper line, you need to restart your computer.
When you boot from your installation CD, choose F6 before you continue trying out the LiveCD. This give you boot option at the bottom of your screen.
At the very end of the line add nolapic acpi=off and hit enter to continue booting from LiveCD. In most cases this should work.
2. The same problem may arise when you do a distribution upgrade or even a kernel upgrade. In that case you need to change your grub.cfg file. Follow these steps:
sudo nano /boot/grub/grub.cfg
Enter your sudo password and it will bring you to your grub menu configuration.
Look for the section that read similar to this:
menuentry 'Ubuntu, with Linux 2.6.38-11-generic' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
set gfxpayload=$linux_gfx_mode
insmod part_msdos
insmod ext2
set root='(hd0,msdos6)'
search --no-floppy --fs-uuid --set=root 337e2841-fc82-61b3-84be-5a9c71ae43b8
linux /boot/vmlinuz-2.6.38-11-generic root=UUID=337e2841-fc82-61b3-84be-5a9c71ae43b8 ro quiet splash vt.handoff=7
initrd /boot/initrd.img-2.6.38-11-generic
}
You want to change the line that I have identified above to read:
linux /boot/vmlinuz-2.6.38-11-generic root=UUID=337e2841-fc82-61b3-84be-5a9c71ae43b8 ro quiet splash vt.handoff=7 nolapic acpi=off
After adding these switches to the boot menu option, press ctrl-X, then save and exit.
This is for a permanent change if you can boot using an older kernel.
3: If you cannot login to an older kernel or recovery mode because of the kernel_thread_helper error, you have to press “e” (without the quotation marks) to edit the boot options when you get the grub menu.
For the kernel you want to use, edit the end of the line that reads
linux /boot/vmlinuz-2.6.38-11-generic root=UUID=337e2841-fc82-61b3-84be-5a9c71ae43b8 ro quiet splash vt.handoff=7
to
linux /boot/vmlinuz-2.6.38-11-generic root=UUID=337e2841-fc82-61b3-84be-5a9c71ae43b8 ro quiet splash vt.handoff=7 nolapic acpi=off
Press Enter and you should be able to boot.
On most Linux/Unix based systems, you can save your Matlab figure as a postscript instead of saving it as a png or jpg. One advantage of saving figures in this manner is that you can save multiple images as separate pages on that .ps document, whereas with png/jpg you have to save each image as a separate file.
To print the current image to postscript, all you need to run is:
print(‘-dpsc2′,’filename’);
To have multiple images appended within the postscript document, you need to use the -append switch.
print(‘-dpsc2′, ‘-append’, ‘filename’);
Your output postscript will have the name filename.ps
To convert the postscripts to pdf format, just run the ps2pdf command in the terminal window:
ps2fpdf filename.ps
The output of this would be filename.pdf
And you’re done.
In order to install l1-SPIRiT Compressed Sensing Parallel MRI, we need to have a couple of programs installed – fftw3, lbz2. Usually you encounter the following error while running build routine in Matlab.
/usr/bin/ld: cannot find -lbz2 collect2: ld returned 1 exit statussudo apt-get install libbz2-dev
After installing libbz2-dev this error is corrected.
Some .avi files tend to have an out of sync audio track, some can’t be scrolled through (forward/reverse), while others might show an message that says the index file needs to be recreated.
Solution is to create a copy of that file that has an index recreated and remove the original and save the copy and all the usual replacement methods.
mencoder -idx files1.avi -ovc copy -oac copy -o file2.avi
Here file1.avi is the input file, and file2 is the output file with corrected index.
The latest version of Ubuntu is heavily based upon Unity environment. Unfortunately Unity has no track record of playing nice with existing gnome programs. For network applications such as VNC, Unity crashes the program with whole bunch of errors. These crashes are observed occasionally in the Ubuntu 11.04 (Natty Narwhal) release, and most certainly in the latest beta 1 release of Ubuntu 11.10 (Oneiric Ocelot).
If you have gotten comfortable with Ubuntu and want to continue using Gnome as the main environment, you can do so by using Linux Mint 11 (Katya). It has the same repositories as Ubuntu and you can even use the ubuntu-restricted-extras and build-essential packages which lets you obtain some of the fonts, codecs and libraries that Ubuntu fetches for you.
Ubuntu is starting to put more emphasis on making their release into an eye-candy, at the cost of reduced functionality. Having used Ubuntu since Dapper Drake days, its sad to ditch it for another distro. IMO Ubuntu 10.04 was the cleanest distro they put out – things have been going downhill after that. Linux Mint on the other hand picked up at the point when Ubuntu started to go dysfunctional. It has everything that Ubuntu should have been. There isn’t much to write about Mint 11. Its very similar to Ubuntu 10.04, has a newer kernel 2.6.38.xx, clean graphics, and the same repositories as Ubuntu. The transition is very easy, and things look a lot more neater in Mint.
To recap: If you are currently using Ubuntu and are afraid to upgrade to the 11.10 release, your fear is quite justified. Make a backup of your /home folder and go for a clean install of Linux Mint instead. I moved to Mint about a month ago and have had a rather smooth sailing so far.
For the first time I was able to get VNC to work with Ubuntu with Gnome session instead of a xterm on gray background. The steps involved were exactly the same as I was following earlier, with one exception: the setup of xstartup in the ~/.vnc folder.
For your xstartup file in ~/.vnc (the “.vnc” folder in
your home directory), you need the following:
#—————————–
#!/bin/sh
# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80×24+10+10 -ls -title “$VNCDESKTOP Desktop” &
gnome-session &
# twm &
#————————
instead of uncommenting the lines as the script suggests, you change the window manager to gnome-session
make sure restart vnc4server
The line which got Gnome working was “gnome-session &”
========================================
Now for all the steps involved (works in Karmic Koala Alpha 2, Ubuntu 9.10, kernel 2.6.30-10)
1. Install ssh server, ssh client, VNC viewer, VNC server, and xinetd
sudo apt-get install openssh-server openssh-client vnc4server xinetd vncviewer
2. Setup the ssh password for your login
ssh-keygen
3. Test out the ssh server by typing in
ssh localhost or ssh your_login@your_ip_address
4. Then create a vnc password
sudo vncpasswd ~/.vncpasswd
5. Edit the xstartup file in ~/.vnc directory
For your xstartup file in ~/.vnc (the “.vnc” folder in
your home directory), you need the following:
—————————–
#!/bin/sh
# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80×24+10+10 -ls -title “$VNCDESKTOP Desktop” &
gnome-session &
# twm &
————————
instead of uncommenting the lines as the script suggests, you change the window manager to gnome-session
6. Create a VNC desktop
vnc4server :1 -geometry 1024×768
7. Then to tunnel into your VNC desktop, first create a SSH tunnel by logging into SSH with the comand:
ssh -L 5901:your_ip_address:5901 your_username@your_ipaddress
8. Finally, load up your VNC desktop
vncviewer localhost:1
And now you are ready to use connect to your machine remotely and use administer the computer remotely.
P.S: If you are using a firewall (hardware or software, you need to get enable port forwarding and unblock ports 22 and 5900-5999 on the Ubuntu machine to allow SSH and VNC to be accessed.
Running scripts in serial order on a multi-core machine will take quite a bit of time. If the tasks are repetitive, the command can be run under GNU Parallel.
You can install it on RPM or Debian based distribution from the GNU Parallel repository. Install the binary that fits your flavour of Linux. Please note that even though the latest release of GNU Parallel has a flavour of Linux associated with it, it runs on most of the older AND newer distributions. For instance I was able to install the April 21st 2011 release of amd_64 RPM on a RHEL5 machine, and it ran just fine for that 8 core machine.
After installation you can try it out on a sample directory by running:
ls -d */ | sed ‘s/\///g’ | parallel zip -r -q {}.zip {}
This will recursively zip all the directories within a given folder, in parallel. By default, it will use up the maximum number of cores, but you can check the man pages of parallel to check how to employ N number of processors to run the task in parallel.
ls *.jpg | parallel convert {} -resize 75% -quality 80% {}
If you have imagemagick installed, you could save a whole bunch of space by converting some of the high-res images to a slightly lower resolution. The above example will resize the images to 75% of their original size with 80% quality. The original images will be overwritten by the resize and downsampled ones. While this is running, you can fire up htop in another terminal window to watch all the processors working in parallel.
Basic formula goes:
Matlab code:
psc=((signal-mean(signal))./signal).*100;
