Skip to content

Getting Help

Man pages, --help and help answer most "which flag" questions faster than a web search, and they match the version installed on the machine. Exams such as RHCSA allow only these sources.

Track: Core · Interview weight: Low

Must-Know Facts

Fact Value Verify with
Man sections 1 commands, 5 file formats, 8 admin commands, 2 system calls, 3 library calls, 7 overviews man -f intro
Page in a section man 5 passwd for the file, man passwd for the command man -f passwd
Search descriptions man -k or apropos; needs an index built by mandb apropos -s 8 'user account'
Builtin help help <builtin>; builtins have no man page of their own help cd
Quick usage <command> --help ls --help
Package docs /usr/share/doc/<package> rpm -qd sudo
Container images Often ship without docs (tsflags=nodocs, dpkg excludes) grep tsflags /etc/dnf/dnf.conf

Man Sections

man -f passwd
man -k '^crontab'
apropos -s 8 'user account'
man -w 5 crontab

Output:

passwd (1)           - change user password
passwd (5)           - password file
crontab (1)          - maintains crontab files for individual users
crontab (5)          - files used to schedule the execution of programs
crontabs (4)         - configuration and scripts for running periodical jobs
userdel (8)          - delete a user account and related files
usermod (8)          - modify a user account
/usr/share/man/man5/crontab.5.gz

Builtins, --help and Package Docs

type cd
help cd | head -3
ls --help | grep -E -- '-h, --human|-t  '

Output:

cd is a shell builtin
cd: cd [-L|[-P [-e]] [-@]] [dir]
    Change the shell working directory.

  -h, --human-readable       with -l and -s, print sizes like 1K 234M 2G etc.
  -t                         sort by time, newest first; see --time

Shell builtins have no man page of their own

man cd returns No manual entry for cd: builtins are documented in help and in man bash.

Package docs and info manuals go beyond man pages

Package documentation lives in /usr/share/doc/<package> (rpm -qd <package> lists it), info coreutils holds the full GNU manuals, and tldr shows example-first summaries.

Common Errors

No manual entry for bash

Cause: the image was installed without documentation. RHEL-family container and cloud images set tsflags=nodocs in /etc/dnf/dnf.conf; minimal Ubuntu images exclude /usr/share/man in /etc/dpkg/dpkg.cfg.d/.

Fix: remove the exclusion, reinstall the packages and rebuild the index (sudo unminimize on Ubuntu):

sudo sed -i 's/^tsflags=nodocs/#tsflags=nodocs/' /etc/dnf/dnf.conf
sudo dnf reinstall -y bash man-pages coreutils-single
sudo mandb -q
man -w bash    # prints /usr/share/man/man1/bash.1.gz once the page is back

Interview Checkpoints

L1: What is the difference between man passwd and man 5 passwd?

Say first: section 1 documents the passwd command; section 5 documents the /etc/passwd file format.

Proof: man -f passwd lists both sections.

Follow-up: Which sections hold system calls and admin commands?

L2: Find the command that changes password aging without knowing its name.

Say first: search the man page descriptions.

Proof: man -k 'password expiry' or apropos -s 1,8 password; chage appears.

Follow-up: Why can apropos return nothing on a fresh install?

L2: Show the help for a shell builtin.

Say first: builtins use help, not man.

Proof: type cd; help cd

Follow-up: How do you list every builtin? (help with no arguments, or enable.)

L2: List the documentation files a package installed.

Say first: query the package database.

Proof: rpm -qd sudo or dpkg -L sudo | grep /usr/share/doc

Follow-up: Where are example configuration files usually kept? (/usr/share/doc/<package>/examples.)

L3: man returns No manual entry for commands that are clearly installed.

Say first: check whether documentation was excluded when packages were installed.

Proof: grep tsflags /etc/dnf/dnf.conf shows nodocs; rpm -qd bash lists files that are missing on disk.

Follow-up: Why do container images exclude documentation?

L3: An exam or air-gapped host has no internet. How do you find the syntax for a file format?

Say first: section 5 man pages and the package's example files.

Proof: man 5 fstab, man 5 crontab, ls /usr/share/doc/<package>.

Follow-up: Which man page describes the filesystem hierarchy? (man 7 hier.)

Captured on Rocky Linux 10.2 and Ubuntu 24.04.4 LTS (iximiuz Labs microVMs, kernel 6.1.167), 2026-09.