Man Page Sections Explained: A Guide For Linux Users
Understanding Man Page Sections
Man pages are the user manuals that provide documentation for commands, system calls, library functions, file formats, and more in Linux and other Unix-like operating systems. They are categorized into sections based on what they document.
Knowing what each man page section covers can help users effectively access the documentation they need. This guide will explain the purpose of the main man page sections and the type of content covered in each.
Section 1: User Commands
Section 1 man pages document commands that can be executed by users from the shell or command line interface to perform tasks and operations in Linux.
These include both external commands that exist as executables in locations like /usr/bin or /bin, as well as built-in shell commands that the bash or other shell provides. Common examples include file manipulation utilities (ls, cd, mkdir), text processing tools (grep, sed, awk), and networking commands (ssh, ping).
The man pages in section 1 contain information on the syntax and options for using these commands, describe what the command does, and provide examples of usage. Checking section 1 should be the first step whenever users need help understanding how to use a specific command in Linux.
Section 2: System Calls
Section 2 contains documentation for system calls, which are functions used by Linux and other Unix-like operating system kernels to provide essential services and resources for programs and processes.
These system calls serve as the interface for making requests to the kernel from user space. Examples include calls for process management (fork, exec), file operations (open, read, write), memory allocation (malloc, free), and interprocess communication.
The man pages in this section document the parameters, return values, errors, and usage details for system calls used by developers when programming in C and other languages. They describe the low-level bindings that application code relies on to leverage kernel functions.
Section 3: C Library Functions
In addition to system calls for accessing kernel services, developers also utilize functions provided by the standard C library (libc) when writing applications targeted for Linux and Unix-like systems.
These library functions perform common programming tasks like string manipulation (strlen, strcmp), memory handling (memcpy, calloc), mathematical operations (sin, log), parsing and formatting data, and more. They serve as building blocks for many userspace applications.
Section 3 of the man pages documents the prototype definitions, arguments, return values, and usage of C library functions that programmers can make use of in their code instead of writing solutions from scratch.
Section 4: Special Files and Drivers
Section 4 contains documentation related to special device files and drivers that can be found in the /dev directory in Unix-like systems such as Linux.
These include device nodes that represent hardware like disks, GPUs, sound cards, as well as virtual devices like /dev/null and random number generators. Man pages in this section describe the device functions and relevant ioctl commands.
For example, serial port devices like /dev/ttyS0 and pseudo terminal slaves will have section 4 man pages discussing parameters for interfacing with them from userspace processes trying to do serial I/O.
Section 5: File Formats
Configuration files, databases, saved game files, and various other standard formats used for storing formatted data in text or binary form often adhere to well-documented specifications.
Section 5 of the man pages covers specifications for such file formats—it aims to comprehensively document the organization and meaning of data within files of a given format so that users and programs can correctly interpret them.
For instance, the man page titled passwd in section 5 describes the format of the /etc/passwd and /etc/shadow files which store user account information. Section 5 also includes man pages for variable file formats like JPEG images and tar archives.
Section 6: Games and Fun Stuff
While most man pages focus on documenting serious system interfaces, commands, and formats, Linux inherited a playful side from Unix history in the form of section 6.
Man pages in this niche section describe fun games and toys like fortune cookies and the amusing aptitude quiz. They retain the standard formatting conventions but take on unusual parodies or witty prose for novelty value.
So while it may not always be hugely informative, aptly invoking section 6 can offer some comic relief from the usual technical man page content.
Section 7: Overview and Conventions
Meta documentation providing orientation, administrative guidelines and standards associated with man pages themselves reside under section 7.
For example, the man man page housed in section 7 offers a high-level overview of formatting conventions like bold and italic text, common section macros, standards on notation and organization of pages, as well as instructions on updating and adding new man pages.
Beyond the man overview itself, additional section 7 entries cover topics like file hierarchies, SQL data types, and public standards followed across man pages originating from various documentation projects.
Section 8: System Administration Commands
Section 8 man pages provide documentation on utilities meant for administrators and power users of Linux and other Unix-like systems.
Commands found here assist with user management, network configuration, process monitoring, storage allocation, boot procedures, system updates, backups, access controls, log analysis, and automated jobs.
Some examples include useradd, iptables, systemctl, lvm, sshd_config, crontab, and logrotate. Administrative privileges are often required for running section 8 commands that manage how the system functions.
Finding the Right Man Page
Man pages for a given topic can reside in multiple sections based on their precise context. Locating the correct section is key to reaching relevant documentation.
Using the section number along with command or function name when invoking man quickly gets you directly to the right page. For example:
- man 1 ls – Command ls documentation
- man 2 write – write system call
- man 3 printf – printf C library function
If section number is unspecified, man will search available stubs in standard order, but this can entail extra steps. For concise access, explicitly including the section number is recommended whenever known.
For reusable objects like C functions and system calls, cross-references between sections also assist with discovering the associated man pages in other areas.
