psql: could not connect to server: No such file or directory

 psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

 If you are trying to open command prompt of postgresql using command psql and it gives above error it means your postgresql server is not started, you need to start it first.

service postgresql start

If it is giving error postgresql: unrecognized service, it means you are not starting correct service, you need to verify the correct name of the service.
Is it postgresql-9.3 or postgresql-9.4 or postgresql-8.4?

Now restart it after confirmation.

service postgresql-9.3 start
or
service postgresql-9.4 start
or
service postgresql-8.4 start

psql: FATAL: Ident authentication failed for user "root"

Postgresql error
psql: FATAL:  Ident authentication failed for user "root"

If you run command psql on terminal as root user and you get the error
psql: FATAL:  Ident authentication failed for user "root"
Here is solution for you. 

To resolve this error, Run these two commands on your terminal.

sudo -u postgres createuser root

It might give you this message
could not change directory to "/root"
Do not worry about it, when it asks
Shall the new role be a superuser? (y/n)
Enter y and press return key.

and the other command is

sudo -u postgres createdb root -O root

Now run command psql on terminal and you will log into postgresql command prompt as user root.

To check the list of postgresql databases, run command
\list

to quit the psql command prompt, run command
\q

Find Orientation of an image captured by a digital camera or mobile / cell phone

Download exiftool tar file from http://www.sno.phy.queensu.ca/~phil/exiftool/ and extract it. Now run these commands.
First change directory.

cd Image-ExifTool-9.78/

Run these commands one by one.

perl Makefile.PL
make
make test
make install

To find the orientation of a camera image run command after installation :

exiftool Orientation -n "/path/of/camera_image.jpg"

Do not use downloaded image, make sure it is clicked by digital camera.

Note : Orientation means the correct position of the image with respect to the camera button when it was clicked.