004
------r--
-------r--
chmod 004 — the ------r-- permission
004 is ------r--. The owner can do nothing, and everyone else gets r.
Who can do what
Three rows for owner, group and others; three columns for read, write and execute. On a folder that last one means the right to go inside.
| Read | Write | Execute | |
|---|---|---|---|
| Owner0 | · | · | · |
| Group0 | · | · | · |
| Others4 | ✓ | · | · |
On a folder the execute bit means going inside. With read but no execute you can list the names yet open nothing in it.
- Symbolic
- ------r--
- ls -l (file)
- -------r--
- ls -l (directory)
- d------r--
- chmod symbolic form
- chmod u=,g=,o=r
- Command
- chmod 004 <file>
- Binary
- 000000100
- Decimal
- 4
- umask (directory)
- 773
- umask (file)
- 662
One digit away
How to read this
- Read is 4, write 2, execute 1; add them for one digit. 7 is 4+2+1, 5 is 4+1.
- The digits are owner, group, others, left to right.
- umask is what gets taken away: from 777 for directories, from 666 for files.
- Special bits (setuid 4000, setgid 2000, sticky 1000) add a fourth digit in front — /tmp is 1777.
Frequently asked questions
Q. What does chmod 004 mean?
It is ------r--. ls -l shows a file as -------r-- and a directory as d------r--.
Q. How is 004 written in rwx form?
It is the same as chmod u=,g=,o=r.
Q. What can other people do with 004?
They get r--.
Q. Which umask produces 004?
773 for directories. The same 662 gives it for files too.