Linux Permissions

• check permissions with sudo -l Understanding Permissions:

• Files and directories have permissions for three user classes: owner, group, and others.

• Each class has three permission types: read, write, and execute.

• Permissions are represented in two ways:

  • Symbolic notation (e.g., rwxr-xr-x)

  • Octal notation (e.g., 755)

Viewing Permissions:

• Use the ls -l command to list file details, including permissions.

Common Permissions:

• r: Read permission allows viewing content.

• w: Write permission allows modifying content.

• x: Execute permission allows running the file as a program (for files).

Changing Permissions:

• Use the chmod command to change permissions.

  • Symbolic notation:

    • +: Add permission.

    • -: Remove permission.

    • =: Set specific permission.

  • Octal notation:

    • Three digits represent permissions for owner, group, and others.

    • Each digit is the sum of permission values (4 for read, 2 for write, 1 for execute).

Ownership and Groups:

• Use the chown command to change file ownership.

• Use the chgrp command to change file group.

• Use the id command to find your user ID and group ID.

Common Commands:

• Change file permissions:

  • Symbolic: chmod ugo+r myfile.txt (add read to all)

  • Octal: chmod 644 myfile.txt (read/write for owner, read for group/others)

• Change owner: chown username:groupname myfile.txt

• Change group: chgrp groupname myfile.txt

• Show current permissions: ls -l myfile.txt

• Set default permissions: umask 022 (sets default to 644 for files)

Security Tips:

• Use the most restrictive permissions necessary.

• Avoid giving write access to unnecessary users.

• Be cautious with chmod commands, especially with root privileges.