Lesson 1

A Unix Administrator must have a strong understanding of file management in Unix-like operating systems, as it is a core aspect of system administration. Below are the fundamental concepts related to file management that a Unix Administrator should understand:

1. File System Hierarchy
   • Understand the structure of the Unix file system, including key directories such as:
     • / (root directory)
     • /bin (essential binaries)
     • /etc (configuration files)
     • /home (user home directories)
     • /var (variable data like logs)
     • /tmp (temporary files)
     • /usr (user-installed software and libraries)
   • Know the purpose of each directory and how they are organized.
2. File Types
   • Recognize the different types of files in Unix:
     • Regular files: Text files, binary files, etc.
     • Directories: Special files that contain references to other files.
     • Symbolic links: Shortcuts to other files or directories.
     • Device files: Represent hardware devices (e.g., /dev/sda).
     • Sockets and pipes: Used for inter-process communication.
3. File Permissions and Ownership
   • Understand how Unix handles file permissions and ownership:
     • Ownership: Files are owned by a user and a group.
     • Permissions: Read (r), write (w), and execute (x) permissions for the owner, group, and others.
     • Use commands like chmod, chown, and chgrp to modify permissions and ownership.
     • Understand the concept of the umask and how it affects default file permissions.
4. File Manipulation Commands
   • Be proficient with common file management commands:
     • ls: List files and directories.
     • cp: Copy files and directories.
     • mv: Move or rename files and directories.
     • rm: Remove files and directories.
     • touch: Create empty files or update timestamps.
     • mkdir and rmdir: Create and remove directories.
     • ln: Create hard and symbolic links.
5. File Searching and Filtering
   • Know how to search and filter files:
     • find: Search for files and directories based on various criteria (name, type, size, etc.).
     • grep: Search for text patterns within files.
     • locate: Quickly find files using a prebuilt database.
     • which and whereis: Locate executable files.
6. File Compression and Archiving
   • Understand how to compress and archive files:
     • tar: Create and extract archive files.
     • gzip, bzip2, xz: Compress and decompress files.
     • zip and unzip: Handle .zip archives.
7. Disk Usage and Quotas
   • Monitor and manage disk usage:
     • df: Display disk space usage for file systems.
     • du: Estimate file and directory space usage.
     • Set and manage disk quotas for users and groups.
8. File System Maintenance
   • Perform file system checks and repairs:
     • fsck: Check and repair file systems.
     • mount and umount: Attach and detach file systems.
     • Understand file system types (e.g., ext4, XFS, ZFS).
9. File Descriptors and Redirection
   • Understand file descriptors and input/output redirection:
     • Standard input (stdin), output (stdout), and error (stderr).
     • Use >, >>, <, and | for redirection and piping.
     • Understand special files like /dev/null and /dev/zero.
10. Backup and Recovery
    • Implement backup strategies for file management:
      • Use tools like rsync, scp, and dd for backups.
      • Understand incremental and full backups.
      • Plan for disaster recovery and file restoration.
11. Security and Access Control
    • Secure files and directories:
      • Use chattr to set immutable flags.
      • Implement Access Control Lists (ACLs) for fine-grained permissions.
      • Monitor file integrity with tools like tripwire or AIDE.
12. Special Files and Directories
    • Understand the purpose of special files and directories:
      • /proc and /sys: Virtual file systems for system and process information.
      • /dev: Device files.
      • /etc/fstab: File system table for mounting partitions.
13. Automation and Scripting
    • Automate file management tasks using shell scripts:
      • Use loops, conditionals, and commands like find and xargs for batch operations.
      • Schedule tasks with cron or at.

By mastering these concepts, a Unix Administrator can effectively manage files and directories, ensuring the system is organized, secure, and efficient. Let me know if you need further details on any of these topics!

Before beginning this course you should be comfortable with the following concepts.

1. Using the ls command to list files
2. Using wildcards (*, ?, and []) to create an efficient shorthand system for specifying file names
3. How to copy, move, or remove files using cp, mv, or rm
4. How to create or remove directories using mkdir and rmdir

• File Management Tasks
  This module will discuss advanced file management tasks. By the end of this module, you will be able to:
  1. List files recursively and list hidden files
  2. Copy a directory
  3. Remove a directory tree
  4. Create a link
  5. Find files on the system

To gain a full picture of the internal operation of filesystems, it is necessary to understand what the user sees, why things are presented the way they are, and what the main concepts are. This module provides an introduction to basic file concepts. Users new to UNIX and those starting to program in the UNIX environment will find these concepts useful. A basic implementation of the

ls program 

helps to reinforce the material presented and provides an introduction to file-related libraries and system calls, a topic that will be expanded upon in the next module. One peculiarity that UNIX introduced was the notion that everything in the UNIX namespace (file tree) is visible as a file and that the same operations can be applied to all file types. Thus one can open and read a directory in the same way in which a file can be opened and read. Of course, this does not always have the desired effect. For example, running the UNIX command cat on a directory will likely produce a screen full of unreadable characters. However, these and other simple concepts are one of the great strengths of UNIX. The following sections provide introductory material which describe file-based concepts and start to paint a picture of how these components fit together.
In the next lesson, advanced ways to list files using the ls command will be discussed.