Tag Archive: Advance


As we saw earlier, Rsync can be a nifty tool to transfer data across the systems in an organization while taking backup. However, its prompt for password during transfers can irritate everytime you transfer. Even having a cron-job for automatic backups using rsync will mean you having to enter password which defeats the purpose of cron-job. Here I will show you how you can use rsync over ssh to sync data across computers without password. That’s right, password less transfers with rsync.

First on your server(IP:192.168.100.101) create a ssh key using ssh-keygen,

#ssh-keygen

It will ask you for a location, hit enter for the default location. Next you’ll be prompted for a pass-phrase, hit enter & confirm it with another enter. We want the pass-phrase to be blank. You’ll get the following.

Generating public/private rsa key pair.
Enter file in which to save the key (root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.

Next we will need to copy the public key to the remote system(192.168.100.102). On the local system(192.168.100.101) enter the following;

#ssh-copy-id -i /root/.ssh/id_rsa.pub 192.168.100.102

You’ll be prompted for password for the remote system. Once you enter it, the key will be copied on the remote host. Now you can use rsync to connect & transfer to the remote system(192.168.100.102) without any password prompt.

#rsync -avz -e ssh /root/Desktop/test root@192.168.100.102:/root/Desktop

Now the transfer will be commenced without any prompt for password. You can transfer your public key to various other systems on your network to facilitate a password-less rsync over ssh.

The ‘Recent’ item under places in nautilus sidebar can be handy for accessing recent files on the system. However it can also be a privacy breach. There seems no easy setting to hide the ‘recent’ entry under places. Hiding the sidebar option will hide it completely. Here is a way to hide the ‘recent’ places under the file manager. Actually this does not hide the recent places, but does not allows any files to be listed there in the first place. After doing the following, you’ll see the ‘recent’ under places but there won’t be files listed in there.

The items shown under the recent are stored in a file which is dynamically modified as the user access the files over the system. Simply delete the file containing the recent items history using the following command.

$rm -rf ~/.local/share/recently-used.xbel

Now you’ll need to logout & relogin for changes to take effect. However this is only a one time solution. You’ll need to manually run this command from time to time to clear the recent items.

If you want to save this hassle, you can do the following changes to clear the recent items from not showing up at all. A permanent fix would be to first delete the above file. Now immediately before you open any of your documents(audio, video, text or any file), open a terminal & do the following.

$cd ~/.local/share/

$touch recently-used.xbel

$su

#chattr +i recently-used.xbel

That’s it & you’re done. Now ‘recent’ items under the sidebar will always be empty. To know more about the chattr command, read this post.

Depth-Of-Field Preview is perhaps the most ignored featured found in camera’s. Most of the people don’t either know of its presence in the first place or if they are aware of it, they don’t know how to use it. To tell you the truth, its not difficult to learn what it does & know how to use it. Its very simple & once you know it, you’ll most often be using it. Let me show you how.

First, let’s talk about Depth-Of-Field(DOF). Depth-Of-Field is one of the most crucial factors when it comes to making a photograph. A good photograph often showcases proper use of Depth-Of-Field. Depth-Of-Field in simpler terms is the area in your photographs which is in acceptable focus(sufficiently sharp). A good photographer should be able to utilize DOF correctly so as to keep the subject as the main focus point which creates an appealing photograph.

As we set an aperture to suit a certain frame & look through the viewfinder on our camera, the camera doesn’t changes the aperture to the one we have set rightaway(Its is changed when you release the shutter). It still shows the image in the viewfinder at the maximum aperture(minimum F no.) the lens allows at a particular focal length. This is done, so you can get a bright viewfinder display & can frame easily. In such a case, if you want to preview the effect of a certain aperture the DOF preview button needs to be pressed & held as you look into the viewfinder. The button is generally found below the lens mount on either of the sides(depending on manufacturer) & often it is unmarked. Now the camera will set the aperture you’ve dialed in & give you a preview as to how it will affect the DOF. However at times, its very difficult to find out how much area is in focus & how much is not in the tiny viewfinder. In such a case(& always), I strongly recommend you use Live View. It is much easier to check the DOF in live view. The procedure remains same, switch the camera’s live-view on & then keep the DOF preview button pressed, the screen should display the DOF changes. Still finding it tough to discern the DOF changes, hit that zoom button(one you use to zoom into images) & you can magnify while you keep holding the DOF preview button. Still want to see the changes more fluidly, tether the camera to your computer & check the DOF preview on big screen else via camera’s HDMI-out attach an external monitor on field.

There you go, you’ve learned DOF Preview. Now try it & see how it can prove useful for shooting macro, portraits & almost all genres of photography.

In the first part, I told you how to make a 18% Grey Card for yourself. Now, its time you pull out that grey card as I’ll teach you how to set ‘Custom White Balance’ while shooting in your Canon EOS DSLR. No need to worry, its fairly simple.

IMP - Shoot Grey Card in the SAME LIGHT

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Do-It-Yourself : 18% Grey Card

If you’re serious about exposure & colour balance in your photographs, you must use an “18% Grey Card”. Though today Auto White Balance has come a long way & gives pretty great results most of the time, it does gets fooled at times under tricky mixed lighting situations. Here the grey card will come at your rescue. It will also prevent a lot of your time during post-processing & save you the hassle of correcting WB & exposure. In first part of this article, I’ll teach you how to make a 18% Grey Card for yourself. I highly recommend to make this DIY 18% Grey Card to understand(practise) about exposure & colour correction. This DIY 18% Grey Card isn’t technically perfect but will still give you close to accurate results in your photographs. Once you get a hang of exposure & colour corrections in depth, consider purchasing the commercially available Kodak 18% Grey Card for accurate results.

Things you’ll require:

1) Image Editing Software supporting Layers. I recommend GIMP, its great & free too.

2) Printer(Alternately go to your nearest cyber-cafe to take a printout)

3) White Card-Board(Thick)

The Instructions:

Click to Enlarge

1) Open GIMP. Hit File>New. In the new file creation dialog box, select A4(300ppi) & click OK.

2) Now go to Layer menu & select ‘Duplicate Layer‘.

3) Now press ‘Shift + B’ to select ‘Bucket Fill Tool’. Ensure that ‘Black’ colour is selected as foreground colour. Now click the cursor on the duplicated layer & the layer should be filled with black colour. Now from the GIMP toolbar adjust its opacity to 50%. Save the file as tiff.

4) Now just take a printout of this file on an A4 paper sheet. After that, cut the printed A4 sheet into four equal pieces & stick the pieces over the white card-board. Ensure you cut the card-board pieces slightly bigger than the grey card pieces so you can hand-hold them without ruining the grey area.

There you’ve it. Your 18% Grey Card is ready to use. Keep these four pieces in a ziplock bag & into your camera bag. In the next article, I’ll teach you how to use these grey cards.

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