UNIX Manual and System Administration

A UNIX system administrator works in diverse environments, managing systems like Ubuntu servers, CentOS clusters, or cloud-based Linux instances. While you may master one environment, new systems (e.g., a different Linux distribution or a BSD variant) can introduce unexpected challenges, such as commands behaving differently. Even in a single environment, the sheer number of commands and options makes memorization impossible. For these reasons, proficiency with the UNIX online manual (accessed via the man command) is a critical skill for system administrators. The man pages provide detailed documentation, but they have limitations:

1. They assume familiarity with the command or program being described.
2. They lack a centralized index, requiring searches across multiple entries.
3. They focus on specific commands or daemons, not broader procedures (e.g., no man page explains how to set up a web server, but you’ll find entries for httpd or nginx).
4. Navigating man pages can feel unintuitive due to their unique structure.

Despite these challenges, mastering a few key commands and understanding the manual’s structure enables effective navigation and use.

The man command is your gateway to UNIX documentation. Here are essential commands and tips for using it effectively:

• View a man page: man ls displays the manual for the ls command.
• Search for a command: man -k user lists commands related to "user" (e.g., useradd, usermod).
• Access a specific section: man 1 ls ensures you get the user command (section 1) for ls.
• Navigate a man page: Use /keyword to search for a term, n to jump to the next match, and q to quit.

For example, to learn about the ls command’s options, run:

man ls

Scroll to the "Options" section to find details on flags like -l (long format) or -a (show hidden files).

Below is a simplified representation of the man page structure for the ls command:

ls(1)	Lists directory contents. Use to display files and directories with optional formatting.
Synopsis	ls [-lahtr] [file ...]
Options	-l: Long format, showing permissions, owner, and size. -a: Include hidden files (starting with .). -t: Sort by modification time.
Files	/etc: Directory often listed with ls /etc to view configuration files.

This example shows how man pages provide command details in a structured format.

The UNIX manual is divided into sections, each covering a specific type of information. The most relevant sections for administrators include user commands, system administration commands, and configuration files. While slight variations exist across UNIX systems (e.g., Linux vs. BSD), the structure is consistent.

The following table outlines key manual sections for system administrators:

Contents	Section (BSD)	Section (System V)
User commands (e.g., ls, cat)	1	1
System calls (e.g., kernel-level functions)	2	2
Library functions (e.g., programming routines)	3	3
Special files and devices (e.g., hardware drivers)	4	7 or 9
Configuration files (e.g., /etc/passwd)	5	4
Miscellaneous (e.g., protocols, standards)	7	5
Admin commands (e.g., useradd, fsck)	8	1M

The following commands are commonly used to manage user accounts and groups:

Command	Description
useradd	Adds a new user account.
usermod	Modifies user account attributes (e.g., home directory, shell).
userdel	Deletes a user account.
groupadd	Adds a new group.
groupmod	Modifies group attributes (e.g., group name).
groupdel	Removes a group.

For example, to add a new user, you might run: man useradd to review options, then execute useradd -m -s /bin/bash username to create a user with a home directory and Bash shell.

Man pages follow a consistent structure:

1. Synopsis: Summarizes the command and its options (e.g., ls [-la]).
2. Description: Explains the command’s purpose and behavior.
3. Options: Details each command-line flag.
4. Files: Lists related configuration or data files.
5. Examples: (Sometimes) Provides usage examples.

Optional arguments are shown in brackets (e.g., [file ...] in ls means the file argument is optional). If multiple versions exist (e.g., BSD vs. System V), both may be documented with their respective paths.

Documenting your custom scripts or tools is a best practice in UNIX administration. The standard approach is to create a man page for each tool. Manual pages are text files named after the command and stored in a man subdirectory (e.g., wgrep.1 for a wgrep command in section 1). Basic man pages are plain text, but for a polished look, use the nroff formatting system. Nroff directives (starting with a period, e.g., .TH for title) control formatting. To learn, study existing man page source files (e.g., /usr/share/man/man1/ls.1).