644
rw-r--r--
-rw-r--r--
chmod 644 — the rw-r--r-- permission
The default for ordinary files: everyone reads, owner writes.
644 is rw-r--r--. The owner gets rw, 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 | |
|---|---|---|---|
| Owner6 | ✓ | ✓ | · |
| Group4 | ✓ | · | · |
| 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
- rw-r--r--
- ls -l (file)
- -rw-r--r--
- ls -l (directory)
- drw-r--r--
- chmod symbolic form
- chmod u=rw,g=r,o=r
- Command
- chmod 644 <file>
- Binary
- 110100100
- Decimal
- 420
- umask (directory)
- 133
- umask (file)
- 022
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 644 mean?
It is rw-r--r--. ls -l shows a file as -rw-r--r-- and a directory as drw-r--r--.
Q. How is 644 written in rwx form?
It is the same as chmod u=rw,g=r,o=r.
Q. What can other people do with 644?
They get r--.
Q. Which umask produces 644?
133 for directories. The same 022 gives it for files too.