CentOS 7 File Permissions and Networking Overview

Overview of Permissions:

• CentOS 7 permissions are defined for files and directories.

• Use ls -l command to see detailed permissions of files and directories.

• Each file has permissions for the owner, group, and others.

Permission Bits:

• Each permission group is represented by three binary bits indicating Read (r), Write (w), and Execute (x):

  • r = Read

  • w = Write

  • x = Execute

Sticky Bit:

• The 10th bit indicates the sticky bit, which is crucial for directory deletion permissions. The sticky bit modifies the delete permission behavior in such a way that only the owner of a file or directory can delete or rename it, even if the directory has write permissions for others.

File Types (Table 11-10):

• d : Directory

• - : Regular file

• c : Character device

• b : Block device

• l : Link

• s : Socket

• p : Named pipe

Permission Types (Table 11-11):

• r-- : Read only

• r-x : Read and execute

• rw- : Read and write

• rwx : Read, write, and execute

User Identification Attribute:

SUID (Set User ID):

• When execute permission is set for the owner, it can be indicated by 's' in place of the 'x' (e.g., -rwSrw-r--).

• Allows programs to run with the owner's permissions, which can be dangerous as it entails security risks (potential for privilege escalation). It could be exploited if a malicious user gains access to such a program, allowing them elevated privileges.

Sticky Bit Explanation:

• Ensures only the owner of a file in a directory can delete it, protecting against accidental or malicious deletions.

• Indicated by t or T in the others' permission column. If the sticky bit is set, the 't' appears in the execute position for the others group, providing an additional layer of security in shared directories.

Chapter Summary

Network Overview:

• Networks consist of interconnected computers.

• Common types: Client/server, peer-to-peer, LANs, WANs.

• Internet Protocol Suite is standard for network communications, allowing various devices to communicate effectively.

Networking Essentials:

• Access to network resources requires an IP address, subnet mask, gateway IP address, and DNS IP address.

• In Windows 10, access resources via File Explorer and the Add Printer Wizard; in CentOS 7, use mount and system-config-printer commands to manage and connect to networked resources efficiently.

File Permissions:

• Enable access control over files, helping securely manage shared projects.

• Be cautious of over-permitting access to files by users, as this can lead to unintentional data loss or security breaches. Always assess the necessity of providing write and execute access, particularly in shared environments.

Key Terms

• client/server: A network architecture where a computer acts either as a client or server.

• Dynamic Host Configuration Protocol (DHCP): Autoconfiguration protocol for IP networks, allowing devices to obtain IP addresses and other network configuration parameters automatically.

• homegroup: Feature in Windows 10 for easy sharing of printers and folders among computers.

• Internet Protocol (IP): Main communications protocol for relaying packets across the Internet, ensuring reliable transmission of data.

• IP address: Numeric label for each device on a network, essential for identifying and locating devices within the network.

• LAN (local area network): Network confined to a small geographic area, typically within a single building or campus.

• MAC address: Unique identifier for a physical device at the data link layer; used for network communication within the same network segment.

• packets: Data units traveling over a network, encapsulating the information for transmission.

• peer-to-peer network: Network where workstations have equivalent capabilities, allowing direct sharing without a central server.

• Samba: CentOS 7 implementation of peer-to-peer networking, enabling file and print services