Changing Linux prompt

PS1=‘aj@cchpc:$’

Working with images

1. Crop image using Imagemagick:
   It removes the white space around the image.

   mogrify -trim *.png 

2. Crop image based upon pixel
   sh convert input.jpg -crop WxH+L+T output.jpg
   where,
   W, H= width and height of the figure;
   L = Distance between the left edge of the image and left side of cropped area.;
   T = Distance between the top of the image and Top of the cropped area.
   

3. Changing resolution

Working with pdf

1. Extract a single/ set of pages from a pdf
   • Using PDFTK :
     pdftk in.pdf cat 2-2 output singlepage.pdf
2. Joining two pdf
   • Using PDFTK pdftk in1.pdf in2.pdf cat output joined.pdf
     
3. Delete a page
   • Using PDFTK pdftk in.pdf cat 1-12 14-end output out1.pdf
4. Cropping PDF
   • Using PDFCROP
     pdfcrop IPFileName.pdf OPFileName.pdf
     Removes white space around the pdf.
     
5. Convert the PDF file to jpg or png
   • Using PDFtoPPM :
     pdftoppm -jpeg -r 300 input.pdf output
   • Using Imagemagik:
     convert -density 150 input.pdf -quality 90 output.png
     Though it may require some explicit permission.
     
6. Repair a pdf pdftk broken.pdf output fixed.pdf

Creating a soft link to some executable

Several time we have a code and its executables in a directory (lets call it code directory) and we have a working folder in which we will be performing tests. Lets call it working directory.

The executable files are present as folloing

./a/very/long/path/to/code/directory/executable_file_name

Now, instead of calling code executable each time from the code we can create a soft link in working directory with the following command

link -s  path_of executable    path_where_to_create link 

e.g. to create its link in present folder we can use

link -s  a_very_long_path_to_code_dir/exename  .

Note: the dot in command (.) represent the current directory.

Accessing the Remote server

Sometime the user require to access the software/applications installed at server. This can be easily achieved in following ways depending upon the platform you are using. Assume the following:
1. Username is ‘HarryPotter’
2. Server IP address is 192.168.8.5

STEPS

1. Open the terminal by “ALT + CTRL + T”.

2. Use the SSH command as following:
   $ssh username@IP_Address
   e.g. $ssh HarryPotter@192.168.8.5

3. After this the server asks for your password. Once you enter the password, you are in.

4. If you want to see the graphics while accessing the remote terminal then you have to use X11 port forwarding. For this you must do following.
   

• On the server your /etc/ssh/sshd_config file should have following settings:
  X11Forwarding yes X11DisplayOffset 10 X11UseLocalhost no
• On the client side your ~/.ssh/config file should have following settings:
  Host * ForwardAgent yes ForwardX11 yes
• Now use following command to connect with server with x11 forwarding
  sh $ssh -v -C -X user@host where,
  -X is for x11
  -C is for compression and
  -v is for verbose to check for warnings.

Transferring the files from one system to another system1.

1. If sending to remote server from computer
   scp /file/to/send username@remote:/where/to/put
   If receiving from remote server to computer
   scp username@remote:/file/to/send /where/to/put

2. Between a remote source and remote receiver.
   scp username@source:/location/to/file username@destination:/where/to/put

Periodic transfer/copy of files/files from server A to B using Rsync

To sync the files from server A (having original copy) to server B (where data to be copied).

1. Install rsync on both servers. apt-get install rsync

2. Generate SSH key on server B (with defaults). ssh-keygen
   The keys can be found in folder: /RootOfServerB/.ssh/id_rsa.pub
   

3. Copy contents of key from B to A

4. Copy contenet in A /RootOfServerA/.ssh/authorized_keys

5. Start sync by running following command at server B sh rsync -avrt --delete --rsh='ssh -p 22' root@SERVER_A_IP_ADDRESS:/path PathServerB rsync -rh --delete --progress root@IP:~/specfem3d-master ~/Documents

6. Setup Cron job (repeated job) /etc/crontab */3 * * * * root rsync -avrt --delete --rsh='ssh -p 22' root@SERVER_A_IP_ADDRESS:/path PathServerB/ >/dev/null 2>&1

Installing BLAS, LAPACK, LAPACKE, etc.

• LAPACK
  https://www.assistedcoding.eu/2017/11/04/how-to-install-lapacke-ubuntu/

  $ sudo apt install liblapack3
  $ sudo apt install liblapack-dev
  $ sudo apt install libopenblas-base
  $ sudo apt install libopenblas-dev
  $ sudo apt install liblapacke-dev
  $ sudo apt install liblapack-dev
  -lm -lblas -llapack -llapacke

• OPENBLAS
  $ sudo apt-get install libopenblas-dev

• FFTW
  sudo apt-get install libfftw3-dev libfftw3-doc