Could not connect : Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

If below condition is not the case then google the error and you will get lots of solutions.

Condition:

You did't do any configurational change in server since last time it was working fine. But after restart mysql daemon is not started and gives the following error.

Error:

"Can't connect to local MySQL server through socket ../mysql.sock'.."

if this is the case then cause is most likely server is out of disk space. Because Mysql daemon tries to create 'mysql.sock' file upon startup and there is no disk space left for this to happen.

Hope this will help you,
Recently I encountered with this problem and googled it. Found a lot of solution results but none of them cured the error.

Some of brilliant quotes

Below are some of my favorite quotes regarding project design, analysis, GUI and so on. I have heard similar ones but i think these are simply perfect by being very concise and clear.

Give users what they actually want, not what they say they want. And whatever you do, don't give them new features just because your competitors have them!
Kathy Sierra

The ability to simplify means to eliminate the unnecessary so that the necessary may speak.
Hans Hofmann

When two elements of an interface conflict or are ambiguous, the behaviour should be that which will least surprise the human user or programmer at the time the conflict arises, because the least surprising behavior will usually be the correct one
Principle (or rule) of least astonishment (or surprise)

PL/SQL Developer ORA-12154

ORA-12154:

TNS:could not resolve the connect identifier specified

There are many reasons you may come across with ORA-12154 error while connecting to Oracle database. Actually ORA-12154 is quite common error and you can google for common solutions. Now, I want to give solution to a weird one which you may hardly find otherwise. I experienced this on Windows 64-bit platform with ODAC 10.2.0.2.21 client installed while connecting to Oracle database from PL/SQL Developer.
First of all, check if tnsping works. Open command window type tnsping SERVICE_NAME. Here SERVICE_NAME is the oracle database you want to connect to and it must already exist in tnsnames.ora file where your client product is installed. If tnsping works it could resolve the alias as shown below.

If tnsping works and still PL/SQL Developer complains about ORA-12154 then check where PL/SQL Developer program is installed. If it is located in an address which contains brackets this is the problem. So uninstall and reinstall it in a location where location address doesn't contain brackets. This is weird! In my case it was C:\Program Files (x86)\PLSQL Developer so worked after i reinstalled in C:\Program Files\PLSQL Developer. I did try a lot before found this bug.
If tnsping does't work you may have problem with tnsnames.ora. Maybe file is inaccessible or is not in correct location or its content's syntax is incorrect or something else. I didn't provide detailed solution for this because there are lot of information about this on the internet.
Hope this helps.