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$ whatis umask anyways

Posted on: 06/01/22 19:26:23
Last edited: 06/01/22 19:26:23

So, linux and other operating systems use files. You might have heard the expression “On Linux, everything is a file.”

And Linux uses lots of files. And if everyone had the same rights to all files, it’d be a mess. Unprivileged users would be able to edit critical system files.

small detour:

So, in conclusion folks, applying personifying traits and giving ‘rights’ to computer programs to do whatever they want will create trouble! I’m talking to you, Github! No reason at all to change from master to main. Completely absurd.

detour ends here

So the ext4 filesystem has permission on files. I can get the permission of a file using the ls command with some fancy options:

# -l stands for long options
$ ls -l articles/whatis-umask.md
-rw-r--r-- 1 john cena 780 May  2 21:03 articles/whatis-umask.md

where john is the owner of the file and cena is the group owner of the file. and the first characters are what matter: -rw-r--r-- that garbougle of characters is weird! let’s put some spaces!

-rw- r-- r--. Okay, looks better. These permissions are for the user, group, and other, respectively. Yes, john and cena come into play. john will have -rw-, cena will have r--, and other will have r--. rw means read, write. r-- means read. rwx means read, write, execute. Yes, execute as in execute programs.

But cool thing is if it’s a directory the x means you can create files within the directory ! Try it out in a temp folder ! try making a new dir, looking at file permissions of a folder with ls -lad folder/ and chmod -xing it. can you create files ? folders ? what happens if you revert the -x ?

what umask actually is

the umask command returns the inverse file mask used to create new files within the current shell. Yes, INVERSE. not the ‘real’ mask you get with the ls command.

EVEN more confusingly, you can run the umask -S command to get a set of friendly-looking permissions like in the ls command which will now return the real file mask, not the inverse. You can set the real permissions for your current shell in the same way by just typing out the permissions you want.

e.g.

umask -S u=rwx,g=rx,o=rx

references

Tags: tecnical linux bored