Linux man command

The man pages are interface to the on-line reference manuals and man command is used to format and display the man pages. The man pages are a user manual that is built by default  into most Linux distributions  and other Unix-like operating systems during installation. Man pages come from various sources and although most of them are similar, it can be contain tables, mathematical equations, and bibliographic references. Man pages are the work result of so many people doing their best to describe the commands and their usage. Manual pages are not designed to be a help system, but they do provide descriptions of the commands themselves. You have to know which page to look for or know how to search for the correct page. Manual pages aren’t designed to be a tutorial on how to use the commands. They are a reference that frequently explains how the command functions, so that you can easily understand its use. There is usually help available from the commands themselves by executing the command with the “–help” option. Try typing in ls –help. Beginners are encouraged to type ls –help | less.

 

Sections of the Linux manual

The man pages are originated from the historical Linux Programmer’s manual.  Each manual contains information for specific types of files which have become the sections listed below.

 

Section           Content Type

1                   User Commands (both executable and shell programs)

2                   System calls (kernel routines invoked from user space)

3                   Library functions (provided by program libraries)

4                   Special files (such as device files)

5                   File formats (for many configuration files and structures)

6                   Game (historical section for amusing programs)

7                   Conventions, standards, and miscellaneous (protocols, file systems)

8                   System administration and privileged commands (maintenance tasks)

9                    Linux kernel API (internal kernel calls)

To distinguish identical topic names in different sections, man page references include the section number in parentheses after the topic. For example, passwd(1) describes the command to change passwords, while passwd(5) explains the /etc/passwd file format for storing local user accounts. To read specific man pages, use man topic. Topic contents display one screen at a time. Use arrow keys for single line scrolling or the space bar for next screen. The man command searches manual sections in a configured order, displaying popular sections first. For example, man passwd displays passwd(1) by default . To display the man page topic from a specific section, include the section number argument: man 5 passwd displays passwd(5).

 

Searching for man pages by keyword

A keyword search of man pages is performed using man -k keyword, which displays a list of keyword-matching man page topics with section numbers.

kubuntu@vm:~$ man -k passwd

chgpasswd (8)        – update group passwords in batch mode

chpasswd (8)         – update passwords in batch mode

gpasswd (1)          – administer /etc/group and /etc/gshadow

grub-mkpasswd-pbkdf2 (1) – generate hashed password for GRUB

lppasswd (1)         – add, change, or delete digest passwords.

mkpasswd (1)         – Overfeatured front end to crypt(3)

pam_localuser (8)    – require users to be listed in /etc/passwd

passwd (1)           – change user password

passwd (1ssl)        – compute password hashes

passwd (5)           – the password file

smbpasswd (5)        – The Samba encrypted password file

smbpasswd (8)        – change a user’s SMB password

update-passwd (8)    – safely update /etc/passwd, /etc/shadow and /etc/group

kubuntu@vm:~$

Popular system administration topics are in sections 1 (user commands), 5 (file formats), and 8 (administrative commands). Administrators using certain troubleshooting tools also use section 2 (system calls). The remaining sections are commonly for programmer reference or advanced administration. Keyword searches relay on an index generated by the mandb(8) command, which must be run as root. The command runs through cron.daily, or anacrontab within an hour of boot if out of date. The man command ‘-K’ option performs full-text page search, not just titles and descriptions like the ‘-k’. A full-text search can use greater systems resources and take more time.

 

Examples of man command

The following command provides the information about the ‘ls’ command.

# man ls

The following displays the man page about the ‘man pages’.

# man man

To display the manual page for the ‘cp’ (copy files) command use the below command.

 #  man cp

 

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