file permissions

What are File Permissions?
- File permissions determine who can read, write, or execute a file or directory.
- Every file has three permission types:
  - Read (r): Ability to view the contents of a file or list a directory’s contents.
  - Write (w): Ability to modify or delete a file or its contents.
  - Execute (x): Ability to run a file as a program or access a directory.

Viewing Permissions
Use ls -l to see permissions for files and directories:
```
$ ls -l
```
Example output:
-rwxr-xr-- 1 user group 4096 Oct 11 10:15 script.sh
- Permission Breakdown:
  - -rwxr-xr--
    - The first character: - (file) or d (directory).
    - Owner: rwx (read, write, execute for the file owner).
    - Group: r-x (read, execute for users in the file's group).
    - Others: r-- (read-only for all others).

Basic Syntax:
```
chmod <permissions> <file>
```
1. Using Numeric Mode
- Permissions can be represented by numbers:
  - 4 = Read (r)
  - 2 = Write (w)
  - 1 = Execute (x)
- Combine these for different roles:
  - Owner | Group | Others: 777 (rwx for all), 644 (rw- for owner, r-- for group and others)
Example:
```
chmod 755 script.sh
```
This gives the owner full access (rwx), while group and others get read and execute access (r-x).
2. Using Symbolic Mode
- Permissions can also be changed with symbols:
  - u = user/owner
  - g = group
  - o = others
  - a = all (user, group, others)
Example:
```
chmod u+x script.sh
```
This adds execute permission to the owner.

Example:
```
chmod g-w file.txt
```
This removes write permission for the group.

Give execute permission to all users:
```
chmod a+x script.sh
```
Remove write permission for others:
```
chmod o-w file.txt
```
Set full permissions for the owner, read-only for group and others:
```
chmod 744 file.txt
```

chown allows you to change the owner and group of a file.
```
chown <owner>:<group> <file>
```
Example: Change the owner to user1 and group to staff:
```
chown user1:staff file.txt
```
Change ownership of a directory recursively:
```
chown -R user1:staff /path/to/directory
```

Use stat to view detailed file permissions and other metadata:
```
stat file.txt
```
This will show the numeric mode (e.g., 0644) and other attributes of the file.

Setuid (Set User ID): Allows a file to be executed with the permissions of its owner.
```
chmod u+s file.sh
```
Setgid (Set Group ID): Ensures new files created in a directory inherit the group of the directory.
```
chmod g+s directory/
```
Sticky Bit: Prevents users from deleting files in a directory unless they own them.
```
chmod +t /shared_directory
```

This expanded section provides an in-depth understanding of file permissions, chmod, chown, and special permission settings in Linux.

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