Linux man (manual) Command

Despite the ‘man’ commands, relative simplicity and appearance of unimportance, the ‘man’ command is, perhaps, one of the most important commands to lean in Linux. 

Why the ‘man’ command important?

The true value of the ‘man’ command is that provides access to the online manuals (documentation), which will be consulted often until Linux commands and functions have to be learned and internalized.  Even after learning the more familiar and commonly used Linux command and functions, one will still need to refer the less commonly used capabilities or to confirm something which has been used in a while.

When some the more arrogant Linux users will sometime tell folks with questions to “read the frickin’ manual” (RTFM), the ‘man’ command is what they are usually talking about.  Although there are other perfectly useful reference materials online (e.g., git documentation project) or commercial books, the ‘man’ command should be the go-to place for documentation.  The reason this is actually very simple, if the command or function is installed in your version or environment instance of Linux, then man pages will be available.  Therefore, usually, there will no need to go search on the internet for answers or carrying books around.

The ‘man’ command syntax

The syntax of the ‘man’ command is simple and easy to learn to use.  In fact, the ‘man’ command is so easy to use that people frequently will not even use options when they use the man command and enter ‘man’ command and the keyword.

‘man’ command syntax

man [options] (keywords)

Simple examples to illustrate how to use the ‘man’ command.

Example to pull up the ‘Man’ command documentation

[blog-server ~]$ man man

In this example, the man command is using ‘man man’ to pull up its own online documentation.

Example to pull up the ‘ls’ command documentation

[blog-server ~]$ man ls

In this example, the man command is using ‘man ls’ to pull up the ‘list directory contents‘ online documentation.

list directory contents

Example to pull up the ‘cp’ command documentation

[blog-server ~]$ man cp

In this example, the man command is using ‘man cp’ to pull up the ‘copy files and directories ‘ online documentation.

Example screenshot of the ‘cp’ (copy files and directories) file command online documentation

How to install locate command in Linux Redhat and Centos

To install the locate command (mlocate) in Redhat or Centos, use the ’YUM’ command, install function. 

  • Logon as ‘root’ or use with ‘sudo’ permissions
  • Then, run a ’man’ command to confirm that the locate command is not already installed: ‘man locate’

Example ‘man’ command (as root user)

[root@blog-server ~]# man locate

  • If the ’man’ documentation page returns, then it is already installed.  If no ’man’ documentation page is returned, then run the ‘yum install’ command.
  • Run the ‘yum install’ command as ‘root’ or ‘sudo’ user:

Example ‘yum install’ command (as root user)

[root@blog-server ~]# yum install mlocate

Example ‘yum install’ command (as sudo user)

[root@blog-server ~]# sudo yum install mlocate

Then run the [root@data-server ~]# updated

Example Run ‘updatedb’ Command (as Root user)

[root@blog-server ~]# updated

Example Run ‘updatedb’ Command (as sudo user)

[root@blog-server ~]# sudo updatedb

How To quit the Linux vi editor without saving changes

To quit the Linux ’vi’ editor without saving any changes which have been made:

To Exit the insert or append mode

  1. From within insert or append mode, press the ‘Esc‘ key.

To Enable VI Command Line

  1. Press the ‘:’ (colon) Key. The cursor should reappear in the lower-left corner of the screen beside a colon prompt.
  2. Then, Enter the ‘q!’ Command and press the ‘Enter’ Key.

Example VI Command Line

: q!

This will quit the Linux VI editor, and all changes the document made in this session will be lost.

Linux Move (mv) Command

The Linux move command (mv) is one of the essential commands, which can be very useful in Linux, Unix, and AIX.  The primary purpose of the move command is obviously to move files, and of course, directories.   The move command may also be used to rename files and to make backups.

Move Command Syntax

$ mv [options] source (file or directory)  destination

Move Command options

option description
mv -f force move by overwriting destination file without prompt
mv -i interactive prompt before overwriting
mv -u update – move when the source is newer than the destination
mv -v verbose – print source and destination files
MV – t explicitly saying to move the file or directory here, rather trying to fit everything into the last argument.
mv * Move all (Multiple) files to a specific director without listing by name

For More move command details see the Linux documentation manuals using the man command

$ man mv

mv command examples

Here are some quick and very simple move command (MV) examples for reference.

Move Move to files  to the /Archive/ directory:

$ mv happy.txt garden.txt /Archive/

Move all “.txt” files in the current directory to subdirectory backup:

$ mv *.txt backup

Move all files in subdirectory ‘backup’ to current directory:

$ mv backup/*

Rename file happy.txt to happy.bak filename:

$ mv happy.txt happy.bak

Rename directory backup to backup2:

$ mv backup backup2

Update – move when happy.txt is newer or missing in target directory:

$ mv -u happy.txt backup

Move happy.txt and prompt before overwrite backup / happy.txt:

$ mv -v happy.txt backup

Linux VI Command – Set Line Number

The “Set Number” command in the VI (visual instrument) text editor seems may not seem like the most useful command.  However, it is more useful than it appears.  Using the “set number” command is a visual aid, which facilitates navigation within the VI editor. 

To Enable Line Number In the VI Editor

The “set Number” command is used to make display line numbers, to enable line numbers:

  • Press the Esc key within the VI editor, if you are currently in insert or append mode.
  • Press the colon key “:”, which will appear at the lower-left corner of the screen.
  • Following the colon enter “set number” command (without quotes) and press enter.

A column of sequential line numbers will then appear at the left side of the screen. Each line number references the text located directly to the right. Now you will know exactly which line is where and be able to enter a colon and the line number you want to move to and move around the document lines with certainty.

To Disable Line Number In the VI Editor

When you are ready to turn offline numbering, again follow the preceding instructions, except this time, enter the following line at the : prompt:

  • Press the Esc key within the VI editor, if you are currently in insert or append mode.
  • Press the colon key “:”, which will appear at the lower-left corner of the screen.
  • Following the colon enter “set nonumber” command (without quotes) and press enter.

To Make The Line Number Enable When You Open VI:

Normally, vi will forget the setting you’ve chosen once you’ve left the editor. You can, however, make the “set Number” command take effect automatically whenever you use vi on a user/account, enter the “set Number” command as a line in the .exrc file in your home directory.

Related References

Use and Advantages of Apache Derby DB


Developed by Apache Software Foundation, Apache Derby DB is a completely free, open-source relational database system developed purely with Java. It has multiple advantages that make it a popular choice for Java applications requiring small to medium-sized databases.

Reliable and Secure

With over 15 years in development, Derby DB had time to grow, add new and improve on the existing components. Even though it has an extremely small footprint – only 3.5MB of all JAR files – Derby is a full-featured ANSI SQL database, supporting all the latest SQL standards, transactions, and security factors.

The small footprint adds to its versatility and portability – Derby can easily be embedded into Java applications with almost no performance impact. It’s extremely easy to install and configure, requiring almost no administration afterward. Once implemented, there is no need to further modify or set up the database at the end user’s computer. Alongside the embedded framework, Derby can also be used in a more familiar server mode.

All documentation containing different manuals for specific versions of Derby can be found on their official website, at :

Cross-Platform Support

Java is compatible with almost all the different platforms, including Windows, Linux, and MacOS. Since Derby DB is implemented completely in Java, it can be easily transferred without the need for different distribution downloads. It can use all types of Java Virtual Machines as long as they’re properly certified. Apache’s Derby includes the Derby code without any modification to the elemental source code.

Derby supports transactions, which are executed for quick and secure data retrieval from the database as well as referential integrity. Even though the stored procedures are made in Java, in the client/server mode Derby can bind to PHP, Python and Perl programming languages. 

All data is encrypted, with support for database triggers to maintain the integrity of the information. Alongside that, custom made functions can be created with any Java library so the users can manipulate the data however they want. 

Embedded and Server Modes

Derby’s embedded mode is usually recommended as a beginner-friendly option. The main differences are in who manages the database along with how it’s stored. 

When Derby is integrated as a whole and becomes a part of the main program, it acts as a persistent data store and the database is managed through the application. It also runs within the Java Virtual Machine of the application. In this mode, no other user is able to access the database – only the app that it is integrated into. As a result of these limits, the embedded mode is most useful for single-user apps.

If it’s run in server mode, the user starts a Derby network server which is tasked with responding to database requests. Derby runs in a Java Virtual Machine that hosts the server. The database is loaded onto the server, waiting for client applications to connect to it. This is the most typical architecture used by most of the other bigger databases, such as MySQL. Server mode is highly beneficial when more than one user needs to have access to the database across the network.

Downloading Derby

Derby has to be downloaded and extracted from the .zip package before being used. Downloads can be found at the Apache’s official website:

Numerous download options are presented on there, depending on the Java version that the package is going to be used with. 

Using Derby requires having Java Development Kit (JDK) pre-installed on the system and then configuring the environment to use the JDBC driver. Official tutorials can be found at:

Running and Manipulating Derby DB

Interacting with Derby is done through the use of ‘ij’ tool, which is an interactive JDBC scripting program. It can be used for running interactive queries and scripts against a Derby database. The ij tool is run through the command shell.

The initial Derby connection command differs depending on whether it’s going to be run in embedded or server mode.

For a tutorial on how to use the connect commands, check out https://www.vogella.com/tutorials/ApacheDerby/article.html.

Some Useful Derby DB Documentation

Derby Reference Manual‎: ‎

Derby Server and Administration Guide‎: ‎

API Reference‎:

Derby Tools and Utilities Guide‎: ‎

ij Basics

In conclusion, Derby DB is a lightweight yet efficient tool that can be integrated into various types of Java applications with ease.