Skip to content

41.File_Permissions_Basics.md

Latest commit

 

History

History
161 lines (118 loc) · 4.39 KB

41.File_Permissions_Basics.md

File metadata and controls

161 lines (118 loc) · 4.39 KB

File Permissions

File permissions describe the allowed operations that different types of users can perform on files or directories.

User Categories

All users are divided into the following four types:

  • User/Owner: Represented by u
  • Group: Represented by g
  • Others: Represented by o
  • All: Represented by a

Use Case: Understanding User Types

Project: DURGASOFT COLLEGE AUTOMATION SYSTEM
This project is divided into multiple modules, with different developers working on each module:

  1. STUDENTS MODULE: Developers A, B, C, D
  2. EMPLOYEES MODULE: Developers X, Y, Z
  3. COURSES MODULE: Developers M, N
  4. INFRASTRUCTURE MODULE: Developers G, H

Example:
Developer 'A' creates a file named demo.txt.

  • User/Owner: A (file creator)
  • Group: B, C, D (team members in the same module)
  • Others: X, Y, Z, M, N, G, H (developers from other modules)

Permission Types

For files and directories, the following types of permissions are available:

  1. r → Read
  2. w → Write
  3. x → Execute
  4. - → No Permission

Table Of File Permissions

Permission Type For Files For Directories
1. Read (r) Read permission for the file means we can view content of the file. Read permission for the directory means we can list out contents of that directory (e.g., use ls command).
2. Write (w) Write permission for the file means we can modify the content of the file. Write permission for the directory means we can modify contents of that directory (e.g., create a new file or delete an existing file).
3. Execute (x) Execute permission for the file means we can execute the file like a normal program. Execute permission for the directory means we can enter into that directory (e.g., use cd command).

Operations Related to Permissions

We can perform three operations to manage permissions:

  • + → Add a permission
  • - → Remove a permission
  • = → Assign specific permissions

chmod Command

The chmod command is used to change file or directory permissions.

Syntax:

$ chmod <user_category><operation><permission> file_name/directory_name

Example:

$ chmod u+x,g+w,o-r demo.txt
  • Add execute permission for the user.
  • Add write permission for the group.
  • Remove read permission for others.

Note: Only the owner or superuser (root) can change file permissions.

Checking File Permissions

Use the ls -l command to check the permissions of an existing file.

Example:

$ ls -l
-rw-r--r-- 1 durgasoft durgasoft 0 Nov 27 21:19 demo.txt

file permissions

Breakdown of Permissions

  • User Permissions: rw- (read and write)
  • Group Permissions: r-- (read only)
  • Others Permissions: r-- (read only)

Order of Permissions:

  • User → Group → Others
  • Read (r) → Write (w) → Execute (x)

Examples of chmod Command

Example 1

$ chmod u+x demo.txt
  • Adds execute permission to the user.

Example 2

$ chmod u+w,g+rw,o+r demo.txt
  • Adds write permission to the user.
  • Adds read and write permissions to the group.
  • Adds read permission to others.

Example 3

$ chmod u+x,g-w,o+w demo.txt
  • Adds execute permission to the user.
  • Removes write permission from the group.
  • Adds write permission to others.

Example 4

$ chmod u=rw,g=rw,o=r demo.txt
  • Sets user permissions to rw-.
  • Sets group permissions to rw-.
  • Sets others' permissions to r--.

### Example 5
```bash
$ chmod a=- demo.txt
  • Removes all permissions for all categories (user, group, others).

Result:

  • User Permissions: ---
  • Group Permissions: ---
  • Others Permissions: ---

Example 6

$ chmod a=rwx demo.txt
  • Grants all permissions (read, write, execute) to all categories (user, group, others).

Result:

  • User Permissions: rwx
  • Group Permissions: rwx
  • Others Permissions: rwx