whatis

Overview

whatis prints single-line descriptions from the man-db whatis index. Use it when you want a one-sentence reminder of what a command or page is without opening the full manual. Same idea as man -f.

It answers “what is this name?” — not “what command does X?” (that’s apropos / man -k).

Syntax

whatis [options] name...
man -f name...

Common Options

Option	Description
-s list	Only these sections (e.g. 1,8 or 5)
-l	Long / multi-line output when available
-r	Interpret name as regex (implementation-dependent)
-w	Wildcard match on names
-v	Verbose diagnostics
-d	Debug (man-db)

Examples with Explanations

Quick one-liners

whatis ls
whatis passwd
whatis passwd chmod mount
man -f ls                   # equivalent

Disambiguate by section

whatis passwd
whatis -s 1 passwd          # the command
whatis -s 5 passwd          # /etc/passwd format
whatis -s 2,3 open          # syscall / libc

Multiple names in scripts

for c in curl wget aria2c; do
  whatis "$c" 2>/dev/null || echo "$c: no man summary"
done

Missing database

# typical message: whatis: nothing appropriate
sudo mandb
whatis ls
whatis systemctl

Minimal Docker images: install man-db and relevant man packages first.

Combine with type / path

type mount
command -v mount
whatis mount
man 8 mount

type shows how the shell runs it; whatis shows what the man index claims it is.

Wildcard / regex (when supported)

whatis -w 'system*'
whatis -r '^ip$'

Verify pages after package install

sudo apt install --reinstall manpages manpages-dev   # Debian/Ubuntu example
sudo mandb
whatis open openat

Understanding Output

Typical line shape:

ls (1)               - list directory contents
passwd (1)           - change user password
passwd (5)           - the password file

Columns: name, (section), short description. Multiple lines appear when the name exists in several sections.

Exit status is non-zero when no entry matches (handy in scripts).

Notes / Pitfalls

• No output / “nothing appropriate” → run sudo mandb, install docs packages, or wrong name.
• Builtins like cd may have thin or missing whatis entries; use help cd.
• Descriptions can be outdated relative to a newer binary if packages diverged; open man when accuracy matters.
• whatis does not search descriptions for keywords — use apropos.
• Localized systems may show translated one-liners; use LANG=C whatis … for English.

2026-relevant notes

• Still the fastest “sanity check” that a tool is installed with documentation on the box.
• Pair with command -v in onboarding scripts: binary present + whatis present = usable offline reference.
• Some distros split man pages into *-doc packages (especially libraries); whatis missing does not always mean the binary is missing.

Related Commands

• apropos / man -k — keyword search across descriptions
• man — full page
• info — Texinfo manuals
• command -v / type — how the shell resolves a name
• mandb — rebuild the whatis database

Additional Resources

• man whatis, man man