When is it okay to check if a file exists?

Question

File systems are volatile. This means that you can\'t trust the result of one operation to still be valid for the next one, even if it\'s the next line of code. You can\'t

Answer 1

In *nix environment a well established method for checking if another copy of the program is already running is to create a lock file. So the check for file existence is used to verify this.