this file is the issue but this is a bit more than a permission issue.
- the server would normally delete this file after mongodb shuts down, but socket files tend to stuck sometimes. delete that socket file and let mongodb create a new one on its next start up
- there might still be another mongodb instance using the port 27017. it might be a lingering instance that kept running after some program crash. if this is the case, you cannot remove socket file. check processes and kill that instance first.
- I hope this is not the case: the disk might be getting corrupted and this socket file might have been written in one of those areas. you may need a disk check.