How many bits on a linux file system is taken up for the permissions of a file?
To add to the other answers:
Traditional Unix permissions are broken down into:
- read (
- write (
- execute file/access directory (
Each of those is stored as a bit, where 1 means permitted and 0 means not permitted.
For example, read only access, typically written
r--, is stored as binary
100, or octal
There are 3 sets of those permissions, which determines the allowed access for:
- the owner of the file
- the group of the file
- all other users
They are all stored together in the same variable, e.g.
rw-r-----, meaning read-write for the owner, read-only for the group, and no access for others, is stored as
So that makes 9 bits.
Then, there are 3 other special bits:
man 1 chmod for details of those.
And finally, the file's type is stored using 4 bits, e.g. whether it is a regular file, or a directory, or a pipe, or a device, or whatever.
These are all stored together in the inode, and together it makes 16 bits.