Commonly used linux help Commands include man, whatis, apropos, -- help, help +, and whatisapropos.

Commonly used linux help Commands include man, whatis, apropos, -- help, help +, and whatisapropos.
Linux help commands

The man command uses more internally to view the Help file, so you can use some shortcut keys of the more command.
When the command and configuration file name are the same, you can use man 1 passwd to view the Command help, man 5 passwd to view the configuration file help.

Two help files (commands and configuration files are the same)
1. Command help
5. configuration file help

1. man view Command help man read Command Information and Press/enter the search content to search in the current text, and press n to jump to the next searched content

2. View configuration file help by man

Cannot be viewed in absolute path; otherwise, the file content is printed.

Man configuration file name

3. Other related commands 3.1 and whatis only view the brief help document of the command.

[Root @ localhost ~] # Whatis ifconfigifconfig (8)-configure the network interface

3.2. apropos only displays the brief help document of the configuration file

[Root @ localhost ~] # Apropos ifconfigifconfig (8)-configuration network interface ifcfg (8)-simplistic script which replaces ifconfig IP managementpifconfig (8)-display information about a network interface

3.3 Add-help after the command to view common Command Options

[Root @ localhost ~] # Ls -- help usage: ls [Option]... [file]... list information about the FILEs (the current directory by default ). sort entries alphabetically if none of-cftuvSUX nor -- sort is specified. mandatory arguments to long options are mandatory for short options too. -a, -- all do not hide any. project-A, -- almost-all. and .. for any project other than author and-l, list the authors of each file-B, -- escape represents unprintable characters in an octal overflow sequence -- block-size = SIZE scale sizes by SIZE Before printing them; e.g ., '-- block-size = M' prints sizes in units of 1,048,576 bytes; see SIZE format below-B, -- ignore-backups do not list implied entries ending ~ -C with-lt: sort by, and show, ctime (time of last modification of file status information); with-l: show ctime and sort by name; otherwise: sort by ctime, newest first-C list entries by columns -- color [= WHEN] colorize the output; WHEN can be 'never ', 'auto ', or 'alway' (the default); more info below-d, -- directory list directories themselves, not their contents-D, -- dired generate output de Signed for Emacs 'd d mode-f do not sort, enable-aU, disable-ls -- color-F, -- classify append indicator (one of */=> @ |) to entries -- file-type likewise, could t do not append '*' -- format = WORD stored SS-x, commas-m, horizontal-x, long-l, single-column-1, verbose-l, vertical-C -- full-time like-l -- time-style = full-iso-g similar to-l, the owner -- group-directories-first group directories before files is not listed; Can be augmented with a -- sort option, but any use of -- sort = none (-U) disables grouping-G, -- no-group in the form of a long list, no output group name-h, -- human-readable and-l together, output file size in easy-to-read format (for example, 1 K 234 M 2G) -- si is similar to above, however, 1000 is used as the base instead of 1024-H, -- dereference-command-line follow symbolic links listed on the command line -- dereference-command-line-symlink-to-dir follow each command line symbolic link that points to a directory -- Hide = PATTERN do not list implied entries matching shell PATTERN (overridden by-a or-A) -- indicator-style = WORD append indicator with style WORD to entry names: none (default ), slash (-p), file-type (-- file-type), classify (-F)-I, -- inode print the index number of each file-I, -- ignore = PATTERN do not list implied entries matching shell PATTERN-k, -- kibibytes default to 1024-byte blocks for disk Usage-l uses a long format to list information-L, -- dereference when the file information of the symbolic link is displayed, display the objects indicated by the symbolic link instead of the information of the symbolic link itself-m all items are separated by commas, and the entire line width-n, -- numeric-uid-gid is similar to-l, however, list UID and GID-N, -- literal, and output unprocessed project names (such as unspecially controlled characters)-o is similar to-l, but do not list information about the group-p, -- indicator-style = slash to add the symbol "/"-q, -- hide-control-chars print? Instead of nongraphic characters -- show-control-chars show nongraphic characters as-is (the default, unless program is 'LS' and output is a terminal)-Q, -- quote-name enclose entry names in double quotes -- quoting-style = WORD use quoting style WORD for entry names: literal, locale, shell, shell-always, c, escape-r, -- reverse-R, -- recursive display subdirectory-s, -- size: displays the size allocated to each file in the form of blocks-S sort by file size -- sort = WORD sort by WORD instead of name: none (-U), size (-S ), time (-t), version (-v), extension (-X) -- time = WORD with-l, show time as WORD instead of default modification time: atime or access or use (-u) ctime or status (-c); also use specified time as sort key if -- sort = time -- time-style = STYLE with-l, show times using style STYLE: full-iso, long-iso, iso, locale, or + FORMAT; FORMAT is interpreted like in 'date'; if FORMAT is FORMAT1
 
  
FORMAT2, then FORMAT1 applies to non-recent files and FORMAT2 to recent files; if STYLE is prefixed with 'posix -', STYLE takes effect only outside the POSIX locale-t sort by modification time, newest first-T, -- tabsize = COLS assume tab stops at each COLS instead of 8-u with-lt: sort by, and show, access time; with-l: show access time and sort by name; otherwise: sort by access time-U do not sort; list entries in directory order-v natural sort of (version) numbers within text-w, -- width = COLS assume screen width instead of current value-x list entries by lines instead of by columns-X sort alphabetically by entry extension-1 list one file per lineSELinux options: -- lcontext Display security context. enable-l. lines will probably be too wide for most displays. -Z, -- context Display security context so it fits on most displays. displays only mode, user, group, security context and file name. -- scontext Display only security context and file name. -- help: displays the help information and exits. -- version: displays the version information and exits. SIZE is an integer and optional unit (example: 10 M is 10*1024*1024 ). unitsare K, M, G, T, P, E, Z, Y (powers of 1024) or KB, MB ,... (powers of 1000 ).
 

3.4. Run the help + command to view Shell built-in commands

Shell built-in commands cannot be found.

[Root @ localhost temp] # help umaskumask: umask [-p] [-S] [mode] displays or sets the file mode mask. Sets the MODE for the user file creation mask. If MODE is omitted, the value of the current mask is printed. If the MODE starts with a number, it is parsed as an octal number; otherwise it is a chmod (1) symbol MODE string that can be received. Option:-p if MDOE mode is omitted, input-S in reusable input format is output in symbolic form. Otherwise, the output exits in octal format: Success is returned, unless an invalid MODE or option is used.