# Access Rights
* Every user has a unique username and is member of 1+ groups.
* Every file and directory has a owner, a group and a set of permission flags.
* Flags specify permissions:
* read, write and execute(rwx)
* owner, group and others (ugo).
* Programs need to have execute (x) permission to run in shell
```
ls -lt
```
#### Permissions are controlled with the commands chmod, chown, chgrp
* Only owner can change permissions of a file
#### chmod
* chmod has 2 different syntaxes
**Syntax 1**
* assign (=), gives(+), or take away(-) permission
* who corresponds to --> u (user), g (group), o (other)
* permission corresponds to --> read (r), write (w), execute (x)
* chmod who=permission
* chmod who+permission
* chmod who-permission
```
ls -l catfile.txt
chmod g=rwx catfile.txt
ls -l catfile.txt
```
```
ls -l catfile.txt
chmod g-w catfile.txt
ls -l catfile.txt
```
```
ls -l catfile.txt
chmod o+x catfile.txt
ls -l catfile.txt
```
**chmod n**
* numeric shortcuts to change mode in a compact way.
* format: chmod n filename
* n is a 3 digit number, values from 0 to 7
* each digit is associated to user, group, other
* examples:
```
ls -l catfile.txt
chmod 644 catfile.txt
ls -l catfile.txt
chmod 700 catfile.txt
ls -l catfile.txt
```
---
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