Meteor: unexpected mongo exit code 100

After you copy of your meteor project folder then this happens

Unexpected mongo exit code 100. Restarting.
Unexpected mongo exit code 100. Restarting.
Unexpected mongo exit code 100. Restarting.
Can't start mongod

MongoDB had an unspecified uncaught exception.
Check to make sure that MongoDB is able to write to its database directory.

when i got this error i got scared, since almost whole project has been built and now this error, which doesn't seems to go

iam talking about Linux ubuntu

Solution is simple
you got to erase
rm .meteor/local/db/mongod.lock
from the project folder

if you are on linux ubuntu, you can check the exact file name by doing "ls" command

login as root again
and then type meteor, it shall work

do not do meteor reset, it will erase your database