Table of Contents Link to heading

• Man Pages
  • Viewing Man Pages
  • Man Page Sections
  • Searching Within a Man Page
  • Man Page Categories
• Finding Commands and Documentation
• Finding Files with locate
• Info Documentation
• Additional Help Sources
  • The –help Option
  • Package Documentation in /usr/share/doc

Man Pages Link to heading

Man pages (manual pages) are the authoritative reference documentation for Linux commands, system calls, library functions, and configuration file formats. Every standard command ships with a man page; third-party packages typically include man pages as part of their installation.

Man pages are reference documentation — they describe what a command does, what options are available, and what files it uses. They are not tutorials. For learning a new tool conceptually, info pages or online guides are better starting points; for looking up a specific option during use, a man page is the fastest resource.

Viewing Man Pages Link to heading

man ls          # open the man page for ls
man 5 passwd    # open section 5 (file format) of the passwd man page

Man pages display in a pager (typically less). Navigation:

Man Page Sections Link to heading

Man pages are organised into named sections, each serving a specific purpose:

The SYNOPSIS section uses a standard notation worth understanding: items in [] are optional; items in {} are required; ... means the item can repeat; | separates mutually exclusive alternatives.

Searching Within a Man Page Link to heading

• /pattern — search forward; press n for next match, N for previous
• Searches are case-sensitive by default; prefix with (?i) for case-insensitive in some pager implementations

Man Page Categories Link to heading

Man pages are divided into numbered sections that organise documentation by type. When two man pages share a name in different sections (e.g., passwd the command vs passwd the file format), sections disambiguate them.

The man command searches sections in order 1 through 9 and returns the first match. To see all sections that have a page for a given name:

man -f passwd       # equivalent to: whatis passwd
# passwd (1)     - change user password
# passwd (5)     - the password file

To open a specific section:

man 5 passwd        # opens the file format documentation

To search all man page descriptions by keyword:

man -k partition    # equivalent to: apropos partition
# lists all man pages whose description mentions "partition"

Finding Commands and Documentation Link to heading

whereis locates the binary, source code, and man page for a command in the standard filesystem locations:

whereis ls
# ls: /bin/ls /usr/share/man/man1/ls.1.gz

Man pages are typically compressed with gzip (.gz extension) — man decompresses them automatically before display.

which finds only the executable in the PATH:

which python3
# /usr/bin/python3

Finding Files with locate Link to heading

locate searches a pre-built database of all files on the system for filenames matching a pattern. It is significantly faster than find for name-based searches because it queries a database rather than walking the live filesystem.

locate passwd           # find all files with "passwd" in the path
locate -b passwd        # match only the basename (filename, not full path)
locate -c passwd        # count matches only, do not list them
locate -b '\passwd'     # exact basename match (backslash anchors the term)

sudo updatedb

When run as a regular user, locate respects filesystem permissions — it will not return results for files the current user cannot access. Root sees everything.

To filter locate output and get detailed metadata:

locate "*.conf" | xargs ls -lh 2>/dev/null

Info Documentation Link to heading

info provides documentation in a hyperlinked, structured format — think of it as a navigable book rather than a single reference page. Info documents break content into nodes (chapters), with hyperlinks to related topics.

info ls             # open the info page for ls
info                # open the top-level info directory

Navigation within info:

The distinction between man and info in practice: man pages are reference documentation (concise, comprehensive, assumes familiarity); info pages are often more tutorial-oriented and explain the rationale behind features. For GNU utilities (which are the majority of what you use on Linux), info pages are typically more detailed than their man page counterparts.

Additional Help Sources Link to heading

The –help Option Link to heading

Most commands support --help (or -h) to print a concise usage summary directly in the terminal:

ls --help
grep --help

This is the fastest way to recall a specific option without leaving the current context. The output is shorter than a man page — useful for quick reference, not for complete documentation.

Package Documentation in /usr/share/doc Link to heading

Third-party packages typically install additional documentation (README files, changelogs, example configurations, licence files) under /usr/share/doc/packagename/. This is where administrators look for setup guides for complex services like databases, web servers, and mail servers.

ls /usr/share/doc/nginx/
ls /usr/share/doc/postgresql/

Files named README, README.Debian, README.md, INSTALL, or changelog.gz are common. Compressed files (.gz) can be read with zcat or zless:

zless /usr/share/doc/nginx/changelog.gz