The umask describes what file-access bits to always eliminate when creating a file, where 1 is execute, 2 is write, and 4 is read. a umask of 777 will always remove all bits, 666 will remove read and write, 000 won't clear any bits at all, etc. A umask of 000 will usually result in rw-rw-rw just because what created the file never asked for the execute bit to be set in the first place; the umask will never give more bits than what the program asked for, just remove specific bits.