What is debian gnu linux

ChapterВ 1.В Definitions and overview

Table of Contents

1.1.В What is this FAQ?

This document gives frequently asked questions (with their answers!) about the Debian distribution (Debian GNU/Linux and others) and about the Debian project. If applicable, pointers to other documentation will be given: we won’t quote large parts of external documentation in this document. You’ll find out that some answers assume some knowledge of Unix-like operating systems. We’ll try to assume as little prior knowledge as possible: answers to general beginners questions will be kept simple.

If you can’t find what you’re looking for in this FAQ, be sure to check out SectionВ 12.1, “What other documentation exists on and for a Debian system?”. If even that doesn’t help, refer to SectionВ 16.2, “Feedback”.

1.2.В What is Debian GNU/Linux?

Debian GNU/Linux is a particular distribution of the Linux operating system, and numerous packages that run on it.

Debian GNU/Linux is:

full featured : Debian includes more than 58000 software packages at present. Users can select which packages to install; Debian provides a tool for this purpose. You can find a list and descriptions of the packages currently available in Debian at any of the Debian mirror sites.

free to use and redistribute : There is no consortium membership or payment required to participate in its distribution and development. All packages that are formally part of Debian GNU/Linux are free to redistribute, usually under terms specified by the GNU General Public License.

The Debian FTP archives also carry approximately 930 software packages (in the non-free and contrib sections), which are distributable under specific terms included with each package.

dynamic : With about 1343 volunteers constantly contributing new and improved code, Debian is evolving rapidly. The FTP archives are updated twice every day.

Most Linux users run a specific distribution of Linux, like Debian GNU/Linux. However, in principle, users could obtain the Linux kernel via the Internet or from elsewhere, and compile it themselves. They could then obtain source code for many applications in the same way, compile the programs, then install them into their systems. For complicated programs, this process can be not only time-consuming but error-prone. To avoid it, users often choose to obtain the operating system and the application packages from one of the Linux distributors. What distinguishes the various Linux distributors are the software, protocols, and practices they use for packaging, installing, and tracking applications packages on users’ systems, combined with installation and maintenance tools, documentation, and other services.

Debian GNU/Linux is the result of a volunteer effort to create a free, high-quality Unix-compatible operating system, complete with a suite of applications. The idea of a free Unix-like system originates from the GNU project, and many of the applications that make Debian GNU/Linux so useful were developed by the GNU project.

For Debian, free has the GNUish meaning (see the Debian Free Software Guidelines). When we speak of free software, we are referring to freedom, not price. Free software means that you have the freedom to distribute copies of free software, that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

The Debian Project was created by Ian Murdock in 1993, initially under the sponsorship of the Free Software Foundation’s GNU project. Today, Debian’s developers think of it as a direct descendent of the GNU project.

Although Debian GNU/Linux itself is free software, it is a base upon which value-added Linux distributions can be built. By providing a reliable, full-featured base system, Debian provides Linux users with increased compatibility, and allows Linux distribution creators to eliminate duplication of effort and focus on the things that make their distribution special. See SectionВ 14.3, “I am making a special Linux distribution for a «vertical market». Can I use Debian GNU/Linux for the guts of a Linux system and add my own applications on top of it?” for more information.

1.3.В OK, now I know what Debian is. what is Linux?!

In short, Linux is the kernel of a Unix-like operating system. It was originally designed for 386 (and better) PCs; today Linux also runs on a dozen of other systems. Linux is written by Linus Torvalds and many computer scientists around the world.

Besides its kernel, a «Linux» system usually has:

a file system that follows the Linux Filesystem Hierarchy Standard http://www.pathname.com/fhs.

a wide range of Unix utilities, many of which have been developed by the GNU project and the Free Software Foundation.

The combination of the Linux kernel, the file system, the GNU and FSF utilities, and the other utilities are designed to achieve compliance with the POSIX (IEEE 1003.1) standard; see Section 4.4, “How source code compatible is Debian with other Unix systems?”.

For more information about Linux, see What is Linux by Linux Online.

1.4.В Does Debian just do GNU/Linux?

Currently, Debian is only available for Linux, but with Debian GNU/Hurd and Debian on BSD kernels, we have started to offer non-Linux-based OSes as a development, server and desktop platform, too. However, these non-linux ports are not officially released yet.

The oldest porting effort is Debian GNU/Hurd.

The Hurd is a set of servers running on top of the GNU Mach microkernel. Together they build the base for the GNU operating system.

Please see https://www.gnu.org/software/hurd for more information about the GNU/Hurd in general, and https://www.debian.org/ports/hurd/ for more information about Debian GNU/Hurd.

A second effort is the port to a BSD kernel. People are working with the FreeBSD kernel.

See https://www.debian.org/ports/#nonlinux for more information about these non-linux ports.

1.5.В What is the difference between Debian GNU/Linux and other Linux distributions? Why should I choose Debian over some other distribution?

These key features distinguish Debian from other Linux distributions:

As stated in the Debian Social Contract, Debian will remain 100% free. Debian is very strict about shipping truly free software. The guidelines used to determine if a work is «free» are provided in The Debian Free Software Guidelines (DFSG).

The Debian package maintenance system:

The entire system, or any individual component of it, can be upgraded in place without reformatting, without losing custom configuration files, and (in most cases) without rebooting the system. Most Linux distributions available today have some kind of package maintenance system; the Debian package maintenance system is unique and particularly robust (see ChapterВ 7, Basics of the Debian package management system).

Whereas many other Linux distributions are developed by individuals, small, closed groups, or commercial vendors, Debian is a major Linux distribution that is being developed by an association of individuals who have made common cause to create a free operating system, in the same spirit as Linux and other free software.

More than 1343 volunteer package maintainers are working on over 58000 packages and improving Debian GNU/Linux. The Debian developers contribute to the project not by writing new applications (in most cases), but by packaging existing software according to the standards of the project, by communicating bug reports to upstream developers, and by providing user support. See also additional information on how to become a contributor in ChapterВ 13, Contributing to the Debian Project.

The Universal Operating System:

Debian comes with more than 58000 packages and runs on 10 architectures. This is far more than is available for any other GNU/Linux distribution. See Section 5.1, “What types of applications and development software are available for Debian GNU/Linux?” for an overview of the provided software and see Section 4.1, “On what hardware architectures/systems does Debian GNU/Linux run?” for a description of the supported hardware platforms.

The Bug Tracking System:

The geographical dispersion of the Debian developers required sophisticated tools and quick communication of bugs and bug-fixes to accelerate the development of the system. Users are encouraged to send bugs in a formal style, which are quickly accessible by WWW archives or via e-mail. See additional information in this FAQ on the management of the bug log in Section 12.4, “Are there logs of known bugs?”.

The Debian Policy:

Debian has an extensive specification of our standards of quality, the Debian Policy. This document defines the qualities and standards to which we hold Debian packages.

For additional information about this, please see our web page about reasons to choose Debian.

1.6.В How does the Debian project fit in or compare with the Free Software Foundation’s GNU project?

The Debian system builds on the ideals of free software first championed by the Free Software Foundation and in particular by Richard Stallman. FSF’s powerful system development tools, utilities, and applications are also a key part of the Debian system.

The Debian Project is a separate entity from the FSF, however we communicate regularly and cooperate on various projects. The FSF explicitly requested that we call our system «Debian GNU/Linux», and we are happy to comply with that request.

The FSF’s long-standing objective is to develop a new operating system called GNU, based on Hurd. Debian is working with FSF on this system, called Debian GNU/Hurd.

1.7.В How does one pronounce Debian and what does this word mean?

The project name is pronounced Deb’-ee-en, with a short e in Deb, and emphasis on the first syllable. This word is a contraction of the names of Debra and Ian Murdock, who founded the project. (Dictionaries seem to offer some ambiguity in the pronunciation of Ian (!), but Ian prefers ee’-en.)

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What is debian gnu linux

The combination of Debian’s philosophy and methodology and the GNU tools, the Linux kernel, and other important free software, form a unique software distribution called Debian GNU/Linux. This distribution is made up of a large number of software packages . Each package in the distribution contains executables, scripts, documentation, and configuration information, and has a maintainer who is primarily responsible for keeping the package up-to-date, tracking bug reports, and communicating with the upstream author(s) of the packaged software. Our extremely large user base, combined with our bug tracking system ensures that problems are found and fixed quickly.

Debian’s attention to detail allows us to produce a high-quality, stable, and scalable distribution. Installations can be easily configured to serve many roles, from stripped-down firewalls to desktop scientific workstations to high-end network servers.

Debian is especially popular among advanced users because of its technical excellence and its deep commitment to the needs and expectations of the Linux community. Debian also introduced many features to Linux that are now commonplace.

For example, Debian was the first Linux distribution to include a package management system for easy installation and removal of software. It was also the first Linux distribution that could be upgraded without requiring reinstallation.

Debian continues to be a leader in Linux development. Its development process is an example of just how well the Open Source development model can work — even for very complex tasks such as building and maintaining a complete operating system.

The feature that most distinguishes Debian from other Linux distributions is its package management system. These tools give the administrator of a Debian system complete control over the packages installed on that system, including the ability to install a single package or automatically update the entire operating system. Individual packages can also be protected from being updated. You can even tell the package management system about software you have compiled yourself and what dependencies it fulfills.

To protect your system against “ Trojan horses ” and other malevolent software, Debian’s servers verify that uploaded packages come from their registered Debian maintainers. Debian packagers also take great care to configure their packages in a secure manner. When security problems in shipped packages do appear, fixes are usually available very quickly. With Debian’s simple update options, security fixes can be downloaded and installed automatically across the Internet.

The primary, and best, method of getting support for your Debian GNU/Linux system and communicating with Debian Developers is through the many mailing lists maintained by the Debian Project (there are more than 276 at this writing). The easiest way to subscribe to one or more of these lists is visit Debian’s mailing list subscription page and fill out the form you’ll find there.

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ChapterВ 1.В GNU/Linux tutorials

Table of Contents

I think learning a computer system is like learning a new foreign language. Although tutorial books and documentation are helpful, you have to practice it yourself. In order to help you get started smoothly, I elaborate a few basic points.

The powerful design of Debian GNU/Linux comes from the Unix operating system, i.e., a multiuser, multitasking operating system. You must learn to take advantage of the power of these features and similarities between Unix and GNU/Linux.

Don’t shy away from Unix oriented texts and don’t rely solely on GNU/Linux texts, as this robs you of much useful information.

If you have been using any Unix-like system for a while with command line tools, you probably know everything I explain here. Please use this as a reality check and refresher.

1.1.В Console basics

1.1.1.В The shell prompt

Upon starting the system, you are presented with the character based login screen if you did not install any GUI environment such as GNOME or KDE desktop system. Suppose your hostname is foo , the login prompt looks as follows.

If you installed a GUI environment, then you can still get to the character based login prompt by Ctrl-Alt-F3, and you can return to the GUI environment via Ctrl-Alt-F2 (see Section 1.1.6, “Virtual consoles” below for more).

At the login prompt, you type your username, e.g. penguin , and press the Enter-key, then type your password and press the Enter-key again.

Following the Unix tradition, the username and password of the Debian system are case sensitive. The username is usually chosen only from the lowercase. The first user account is usually created during the installation. Additional user accounts can be created with adduser (8) by root.

The system starts with the greeting message stored in » /etc/motd » (Message Of The Day) and presents a command prompt.

Now you are in the shell. The shell interprets your commands.

1.1.2.В The shell prompt under GUI

If you installed a GUI environment during the installation, you are presented with the graphical login screen upon starting your system. You type your username and your password to login to the non-privileged user account. Use tab to navigate between username and password, or use the primary click of the mouse.

You can gain the shell prompt under GUI environment by starting a x-terminal-emulator program such as gnome-terminal (1), rxvt (1) or xterm (1). Under the GNOME Desktop environment, press SUPER-key (Windows-key) and typing in «terminal» to the search prompt does the trick.

Under some other Desktop systems (like fluxbox ), there may be no obvious starting point for the menu. If this happens, just try (right) clicking the background of the desktop screen and hope for a menu to pop-up.

1.1.3.В The root account

The root account is also called superuser or privileged user. From this account, you can perform the following system administration tasks.

Read, write, and remove any files on the system irrespective of their file permissions

Set file ownership and permissions of any files on the system

Set the password of any non-privileged users on the system

Login to any accounts without their passwords

This unlimited power of root account requires you to be considerate and responsible when using it.

Never share the root password with others.

File permissions of a file (including hardware devices such as CD-ROM etc. which are just another file for the Debian system) may render it unusable or inaccessible by non-root users. Although the use of root account is a quick way to test this kind of situation, its resolution should be done through proper setting of file permissions and user’s group membership (see SectionВ 1.2.3, “Filesystem permissions”).

1.1.4.В The root shell prompt

Here are a few basic methods to gain the root shell prompt by using the root password.

Type root at the character based login prompt.

Type » su -l » from any user shell prompt.

This does not preserve the environment of the current user.

Type » su » from any user shell prompt.

This preserves some of the environment of the current user.

1.1.5.В GUI system administration tools

When your desktop menu does not start GUI system administration tools automatically with the appropriate privilege, you can start them from the root shell prompt of the terminal emulator, such as gnome-terminal (1), rxvt (1), or xterm (1). See Section 1.1.4, “The root shell prompt” and Section 7.8, “X server connection”.

	Warning

Never start the GUI display/session manager under the root account by typing in root to the prompt of the display manager such as gdm3 (1).

Never run untrusted remote GUI program under X Window when critical information is displayed since it may eavesdrop your X screen.

1.1.6.В Virtual consoles

In the default Debian system, there are six switchable VT100-like character consoles available to start the command shell directly on the Linux host. Unless you are in a GUI environment, you can switch between the virtual consoles by pressing the Left-Alt-key and one of the F1 — F6 keys simultaneously. Each character console allows independent login to the account and offers the multiuser environment. This multiuser environment is a great Unix feature, and very addictive.

If you are in the GUI environment, you gain access to the character console 3 by pressing Ctrl-Alt-F3 key, i.e., the left-Ctrl-key , the left-Alt-key , and the F3-key are pressed together. You can get back to the GUI environment, normally running on the virtual console 2, by pressing Alt-F2 .

You can alternatively change to another virtual console, e.g. to the console 3, from the commandline.

1.1.7.В How to leave the command prompt

You type Ctrl-D , i.e., the left-Ctrl-key and the d-key pressed together, at the command prompt to close the shell activity. If you are at the character console, you return to the login prompt with this. Even though these control characters are referred as «control D» with the upper case, you do not need to press the Shift-key. The short hand expression, ^D , is also used for Ctrl-D . Alternately, you can type «exit».

If you are at x-terminal-emulator (1), you can close x-terminal-emulator window with this.

1.1.8.В How to shutdown the system

Just like any other modern OS where the file operation involves caching data in memory for improved performance, the Debian system needs the proper shutdown procedure before power can safely be turned off. This is to maintain the integrity of files, by forcing all changes in memory to be written to disk. If the software power control is available, the shutdown procedure automatically turns off power of the system. (Otherwise, you may have to press power button for few seconds after the shutdown procedure.)

You can shutdown the system under the normal multiuser mode from the commandline.

You can shutdown the system under the single-user mode from the commandline.

1.1.9.В Recovering a sane console

When the screen goes berserk after doing some funny things such as » cat some-binary-file «, type » reset » at the command prompt. You may not be able to see the command echoed as you type. You may also issue » clear » to clean up the screen.

1.1.10.В Additional package suggestions for the newbie

Although even the minimal installation of the Debian system without any desktop environment tasks provides the basic Unix functionality, it is a good idea to install few additional commandline and curses based character terminal packages such as mc and vim with apt-get (8) for beginners to get started by the following.

If you already had these packages installed, no new packages are installed.

TableВ 1.1.В List of interesting text-mode program packages

	Warning

package	popcon	size	description
mc	V:55, I:234	1492	A text-mode full-screen file manager
sudo	V:597, I:809	4589	A program to allow limited root privileges to users
vim	V:102, I:404	3286	Unix text editor Vi IMproved, a programmers text editor (standard version)
vim-tiny	V:57, I:969	1574	Unix text editor Vi IMproved, a programmers text editor (compact version)
emacs-nox	V:4, I:19	18364	GNU project Emacs, the Lisp based extensible text editor
w3m	V:25, I:252	2367	Text-mode WWW browsers
gpm	V:11, I:16	540	The Unix style cut-and-paste on the text console (daemon)

It may be a good idea to read some informative documentations.

TableВ 1.2.В List of informative documentation packages

package	popcon	size	description
doc-debian	I:850	166	Debian Project documentation, (Debian FAQ) and other documents
debian-policy	I:29	4306	Debian Policy Manual and related documents
developers-reference	I:6	1916	Guidelines and information for Debian developers
debmake-doc	I:0	10989	Guide for Debian Maintainers
debian-history	I:1	4285	History of the Debian Project
debian-faq	I:846	817	Debian FAQ

You can install some of these packages by the following.

1.1.11.В An extra user account

If you do not want to use your main user account for the following training activities, you can create a training user account, e.g. fish by the following.

Answer all questions.

This creates a new account named as fish . After your practice, you can remove this user account and its home directory by the following.

1.1.12.В sudo configuration

For the typical single user workstation such as the desktop Debian system on the laptop PC, it is common to deploy simple configuration of sudo (8) as follows to let the non-privileged user, e.g. penguin , to gain administrative privilege just with his user password but without the root password.

Alternatively, it is also common to do as follows to let the non-privileged user, e.g. penguin , to gain administrative privilege without any password.

This trick should only be used for the single user workstation which you administer and where you are the only user.

Do not set up accounts of regular users on multiuser workstation like this because it would be very bad for system security.

	Warning

The password and the account of the penguin in the above example requires as much protection as the root password and the root account.

Administrative privilege in this context belongs to someone authorized to perform the system administration task on the workstation. Never give some manager in the Admin department of your company or your boss such privilege unless they are authorized and capable.

For providing access privilege to limited devices and limited files, you should consider to use group to provide limited access instead of using the root privilege via sudo (8).

With more thoughtful and careful configuration, sudo (8) can grant limited administrative privileges to other users on a shared system without sharing the root password. This can help with accountability with hosts with multiple administrators so you can tell who did what. On the other hand, you might not want anyone else to have such privileges.

1.1.13.В Play time

Now you are ready to play with the Debian system without risks as long as you use the non-privileged user account.

This is because the Debian system is, even after the default installation, configured with proper file permissions which prevent non-privileged users from damaging the system. Of course, there may still be some holes which can be exploited but those who worry about these issues should not be reading this section but should be reading Securing Debian Manual.

We learn the Debian system as a Unix-like system with the following.

1.2.В Unix-like filesystem

In GNU/Linux and other Unix-like operating systems, files are organized into directories. All files and directories are arranged in one big tree rooted at » / «. It’s called a tree because if you draw the filesystem, it looks like a tree but it is upside down.

These files and directories can be spread out over several devices. mount (8) serves to attach the filesystem found on some device to the big file tree. Conversely, umount (8) detaches it again. On recent Linux kernels, mount (8) with some options can bind part of a file tree somewhere else or can mount filesystem as shared, private, slave, or unbindable. Supported mount options for each filesystem are available in » /usr/share/doc/linux-doc-*/Documentation/filesystems/ «.

Directories on Unix systems are called folders on some other systems. Please also note that there is no concept for drive such as » A: » on any Unix system. There is one filesystem, and everything is included. This is a huge advantage compared to Windows.

1.2.1.В Unix file basics

Here are some Unix file basics.

Filenames are case sensitive . That is, » MYFILE » and » MyFile » are different files.

The root directory means root of the filesystem referred as simply » / «. Don’t confuse this with the home directory for the root user: » /root «.

Every directory has a name which can contain any letters or symbols except » / « . The root directory is an exception; its name is » / » (pronounced «slash» or «the root directory») and it cannot be renamed.

Each file or directory is designated by a fully-qualified filename , absolute filename , or path , giving the sequence of directories which must be passed through to reach it. The three terms are synonymous.

All fully-qualified filenames begin with the » / » directory, and there’s a » / » between each directory or file in the filename. The first » / » is the top level directory, and the other » / «‘s separate successive subdirectories, until we reach the last entry which is the name of the actual file. The words used here can be confusing. Take the following fully-qualified filename as an example: » /usr/share/keytables/us.map.gz «. However, people also refers to its basename » us.map.gz » alone as a filename.

The root directory has a number of branches, such as » /etc/ » and » /usr/ «. These subdirectories in turn branch into still more subdirectories, such as » /etc/init.d/ » and » /usr/local/ «. The whole thing viewed collectively is called the directory tree . You can think of an absolute filename as a route from the base of the tree (» / «) to the end of some branch (a file). You also hear people talk about the directory tree as if it were a family tree encompassing all direct descendants of a single figure called the root directory (» / «): thus subdirectories have parents , and a path shows the complete ancestry of a file. There are also relative paths that begin somewhere other than the root directory. You should remember that the directory » ../ » refers to the parent directory. This terminology also applies to other directory like structures, such as hierarchical data structures.

There’s no special directory path name component that corresponds to a physical device, such as your hard disk. This differs from RT-11, CP/M, OpenVMS, MS-DOS, AmigaOS, and Microsoft Windows, where the path contains a device name such as » C:\ «. (However, directory entries do exist that refer to physical devices as a part of the normal filesystem. See SectionВ 1.2.2, “Filesystem internals”.)

While you can use almost any letters or symbols in a file name, in practice it is a bad idea to do so. It is better to avoid any characters that often have special meanings on the command line, including spaces, tabs, newlines, and other special characters: < >( ) [ ] ‘ ` » \ / > . If you want to separate words in a name, good choices are the period, hyphen, and underscore. You could also capitalize each word, » LikeThis «. Experienced Linux users tend to avoid spaces in filenames.

The word «root» can mean either «root user» or «root directory». The context of their usage should make it clear.

The word path is used not only for fully-qualified filename as above but also for the command search path . The intended meaning is usually clear from the context.

The detailed best practices for the file hierarchy are described in the Filesystem Hierarchy Standard (» /usr/share/doc/debian-policy/fhs/fhs-2.3.txt.gz » and hier (7)). You should remember the following facts as the starter.

TableВ 1.3.В List of usage of key directories

	Caution

directory	usage of the directory
/	the root directory
/etc/	system wide configuration files
/var/log/	system log files
/home/	all the home directories for all non-privileged users

1.2.2.В Filesystem internals

Following the Unix tradition , the Debian GNU/Linux system provides the filesystem under which physical data on hard disks and other storage devices reside, and the interaction with the hardware devices such as console screens and remote serial consoles are represented in an unified manner under » /dev/ «.

Each file, directory, named pipe (a way two programs can share data), or physical device on a Debian GNU/Linux system has a data structure called an inode which describes its associated attributes such as the user who owns it (owner), the group that it belongs to, the time last accessed, etc. The idea of representing just about everything in the filesystem was a Unix innovation, and modern Linux kernels have developed this idea ever further. Now, even information about processes running in the computer can be found in the filesystem.

This abstract and unified representation of physical entities and internal processes is very powerful since this allows us to use the same command for the same kind of operation on many totally different devices. It is even possible to change the way the kernel works by writing data to special files that are linked to running processes.

If you need to identify the correspondence between the file tree and the physical entity, execute mount (8) with no arguments.

1.2.3.В Filesystem permissions

Filesystem permissions of Unix-like system are defined for three categories of affected users.

The user who owns the file ( u )

Other users in the group which the file belongs to ( g )

All other users ( o ) also referred to as «world» and «everyone»

For the file, each corresponding permission allows following actions.

The read ( r ) permission allows owner to examine contents of the file.

The write ( w ) permission allows owner to modify the file.

The execute ( x ) permission allows owner to run the file as a command.

For the directory, each corresponding permission allows following actions.

The read ( r ) permission allows owner to list contents of the directory.

The write ( w ) permission allows owner to add or remove files in the directory.

The execute ( x ) permission allows owner to access files in the directory.

Here, the execute permission on a directory means not only to allow reading of files in that directory but also to allow viewing their attributes, such as the size and the modification time.

ls (1) is used to display permission information (and more) for files and directories. When it is invoked with the » -l » option, it displays the following information in the order given.

Type of file (first character)

Access permission of the file (nine characters, consisting of three characters each for user, group, and other in this order)

Number of hard links to the file

Name of the user who owns the file

Name of the group which the file belongs to

Size of the file in characters (bytes)

Date and time of the file (mtime)

Name of the file

TableВ 1.4.В List of the first character of » ls -l » output

character	meaning
—	normal file
d	directory
l	symlink
c	character device node
b	block device node
p	named pipe
s	socket

chown (1) is used from the root account to change the owner of the file. chgrp (1) is used from the file’s owner or root account to change the group of the file. chmod (1) is used from the file’s owner or root account to change file and directory access permissions. Basic syntax to manipulate a foo file is the following.

For example, you can make a directory tree to be owned by a user foo and shared by a group bar by the following.

There are three more special permission bits.

The set user ID bit ( s or S instead of user’s x )

The set group ID bit ( s or S instead of group’s x )

The sticky bit ( t or T instead of other’s x )

Here the output of » ls -l » for these bits is capitalized if execution bits hidden by these outputs are unset .

Setting set user ID on an executable file allows a user to execute the executable file with the owner ID of the file (for example root ). Similarly, setting set group ID on an executable file allows a user to execute the executable file with the group ID of the file (for example root ). Because these settings can cause security risks, enabling them requires extra caution.

Setting set group ID on a directory enables the BSD-like file creation scheme where all files created in the directory belong to the group of the directory.

Setting the sticky bit on a directory prevents a file in the directory from being removed by a user who is not the owner of the file. In order to secure contents of a file in world-writable directories such as » /tmp » or in group-writable directories, one must not only reset the write permission for the file but also set the sticky bit on the directory. Otherwise, the file can be removed and a new file can be created with the same name by any user who has write access to the directory.

Here are a few interesting examples of file permissions.

There is an alternative numeric mode to describe file permissions with chmod (1). This numeric mode uses 3 to 4 digit wide octal (radix=8) numbers.

TableВ 1.5.В The numeric mode for file permissions in chmod (1) commands

digit	meaning
1st optional digit	sum of set user ID (=4), set group ID (=2), and sticky bit (=1)
2nd digit	sum of read (=4), write (=2), and execute (=1) permissions for user
3rd digit	ditto for group
4th digit	ditto for other

This sounds complicated but it is actually quite simple. If you look at the first few (2-10) columns from » ls -l » command output and read it as a binary (radix=2) representation of file permissions («-» being «0» and «rwx» being «1»), the last 3 digit of the numeric mode value should make sense as an octal (radix=8) representation of file permissions to you.

For example, try the following

If you need to access information displayed by » ls -l » in shell script, you should use pertinent commands such as test (1), stat (1) and readlink (1). The shell builtin such as » [ » or » test » may be used too.

1.2.4.В Control of permissions for newly created files: umask

What permissions are applied to a newly created file or directory is restricted by the umask shell builtin command. See dash (1), bash (1), and builtins (7).

TableВ 1.6.В The umask value examples

umask	file permissions created	directory permissions created	usage
0022	-rw-r—r—	-rwxr-xr-x	writable only by the user
0002	-rw-rw-r—	-rwxrwxr-x	writable by the group

The Debian system uses a user private group (UPG) scheme as its default. A UPG is created whenever a new user is added to the system. A UPG has the same name as the user for which it was created and that user is the only member of the UPG. UPG scheme makes it safe to set umask to 0002 since every user has their own private group. (In some Unix variants, it is quite common to setup all normal users belonging to a single users group and is a good idea to set umask to 0022 for security in such cases.)

Enable UPG by putting » umask 002 » in the

1.2.5.В Permissions for groups of users (group)

In order to make group permissions to be applied to a particular user, that user needs to be made a member of the group using » sudo vigr » for /etc/group and » sudo vigr -s » for /etc/gshadow . You need to login after logout (or run » exec newgrp «) to enable the new group configuration.

Alternatively, you may dynamically add users to groups during the authentication process by adding » auth optional pam_group.so » line to » /etc/pam.d/common-auth » and setting » /etc/security/group.conf «. (See ChapterВ 4, Authentication and access controls.)

The hardware devices are just another kind of file on the Debian system. If you have problems accessing devices such as CD-ROM and USB memory stick from a user account, you should make that user a member of the relevant group.

Some notable system-provided groups allow their members to access particular files and devices without root privilege.

TableВ 1.7.В List of notable system-provided groups for file access

group	description for accessible files and devices
dialout	full and direct access to serial ports (» /dev/ttyS3 «)
dip	limited access to serial ports for Dialup IP connection to trusted peers
cdrom	CD-ROM, DVD+/-RW drives
audio	audio device
video	video device
scanner	scanner(s)
adm	system monitoring logs
staff	some directories for junior administrative work: » /usr/local «, » /home «

You need to belong to the dialout group to reconfigure modem, dial anywhere, etc. But if root creates pre-defined configuration files for trusted peers in » /etc/ppp/peers/ «, you only need to belong to the dip group to create Dialup IP connection to those trusted peers using pppd (8), pon (1), and poff (1) commands.

Some notable system-provided groups allow their members to execute particular commands without root privilege.

TableВ 1.8.В List of notable system provided groups for particular command executions

group	accessible commands
sudo	execute sudo without their password
lpadmin	execute commands to add, modify, and remove printers from printer databases

For the full listing of the system provided users and groups, see the recent version of the «Users and Groups» document in » /usr/share/doc/base-passwd/users-and-groups.html » provided by the base-passwd package.

See passwd (5), group (5), shadow (5), newgrp (1), vipw (8), vigr (8), and pam_group (8) for management commands of the user and group system.

1.2.6.В Timestamps

There are three types of timestamps for a GNU/Linux file.

TableВ 1.9.В List of types of timestamps

type	meaning (historic Unix definition)
mtime	the file modification time ( ls -l )
ctime	the file status change time ( ls -lc )
atime	the last file access time ( ls -lu )

ctime is not file creation time.

The actual value of atime on GNU/Linux system may be different from that of the historic Unix definition.

Overwriting a file changes all of the mtime , ctime , and atime attributes of the file.

Changing ownership or permission of a file changes the ctime and atime attributes of the file.

Reading a file changes the atime attribute of the file on the historic Unix system.

Reading a file changes the atime attribute of the file on the GNU/Linux system if its filesystem is mounted with » strictatime «.

Reading a file for the first time or after one day changes the atime attribute of the file on the GNU/Linux system if its filesystem is mounted with » relatime «. (default behavior since Linux 2.6.30)

Reading a file doesn’t change the atime attribute of the file on the GNU/Linux system if its filesystem is mounted with » noatime «.

The » noatime » and » relatime » mount options are introduced to improve the filesystem read performance under the normal use cases. Simple file read operation under the » strictatime » option accompanies the time-consuming write operation to update the atime attribute. But the atime attribute is rarely used except for the mbox (5) file. See mount (8).

Use touch (1) command to change timestamps of existing files.

For timestamps, the ls command outputs localized strings under non-English locale (» fr_FR.UTF-8 «).

1.2.7.В Links

There are two methods of associating a file » foo » with a different filename » bar «.

Duplicate name for an existing file

Special file that points to another file by name

See the following example for changes in link counts and the subtle differences in the result of the rm command.

The hardlink can be made within the same filesystem and shares the same inode number which the » -i » option with ls (1) reveals.

The symlink always has nominal file access permissions of » rwxrwxrwx «, as shown in the above example, with the effective access permissions dictated by permissions of the file that it points to.

It is generally a good idea not to create complicated symbolic links or hardlinks at all unless you have a very good reason. It may cause nightmares where the logical combination of the symbolic links results in loops in the filesystem.

It is generally preferable to use symbolic links rather than hardlinks unless you have a good reason for using a hardlink.

The » . » directory links to the directory that it appears in, thus the link count of any new directory starts at 2. The » .. » directory links to the parent directory, thus the link count of the directory increases with the addition of new subdirectories.

If you are just moving to Linux from Windows, it soon becomes clear how well-designed the filename linking of Unix is, compared with the nearest Windows equivalent of «shortcuts». Because it is implemented in the filesystem, applications can’t see any difference between a linked file and the original. In the case of hardlinks, there really is no difference.

1.2.8.В Named pipes (FIFOs)

A named pipe is a file that acts like a pipe. You put something into the file, and it comes out the other end. Thus it’s called a FIFO, or First-In-First-Out: the first thing you put in the pipe is the first thing to come out the other end.

If you write to a named pipe, the process which is writing to the pipe doesn’t terminate until the information being written is read from the pipe. If you read from a named pipe, the reading process waits until there is nothing to read before terminating. The size of the pipe is always zero — it does not store data, it just links two processes like the functionality offered by the shell » | » syntax. However, since this pipe has a name, the two processes don’t have to be on the same command line or even be run by the same user. Pipes were a very influential innovation of Unix.

For example, try the following

1.2.9.В Sockets

Sockets are used extensively by all the Internet communication, databases, and the operating system itself. It is similar to the named pipe (FIFO) and allows processes to exchange information even between different computers. For the socket, those processes do not need to be running at the same time nor to be running as the children of the same ancestor process. This is the endpoint for the inter process communication (IPC). The exchange of information may occur over the network between different hosts. The two most common ones are the Internet socket and the Unix domain socket.

» netstat -an » provides a very useful overview of sockets that are open on a given system.

1.2.10.В Device files

Device files refer to physical or virtual devices on your system, such as your hard disk, video card, screen, or keyboard. An example of a virtual device is the console, represented by » /dev/console «.

There are 2 types of device files.

Character device

Accessed one character at a time

1 character = 1 byte

E.g. keyboard device, serial port, …

Block device

accessed in larger units called blocks

1 block > 1 byte

E.g. hard disk, …

You can read and write device files, though the file may well contain binary data which may be an incomprehensible-to-humans gibberish. Writing data directly to these files is sometimes useful for the troubleshooting of hardware connections. For example, you can dump a text file to the printer device » /dev/lp0 » or send modem commands to the appropriate serial port » /dev/ttyS0 «. But, unless this is done carefully, it may cause a major disaster. So be cautious.

For the normal access to a printer, use lp (1).

The device node number are displayed by executing ls (1) as the following.

» /dev/sda » has the major device number 8 and the minor device number 0. This is read/write accessible by users belonging to the disk group.

» /dev/sr0 » has the major device number 11 and the minor device number 0. This is read/write accessible by users belonging to the cdrom group.

» /dev/ttyS0 » has the major device number 4 and the minor device number 64. This is read/write accessible by users belonging to the dialout group.

» /dev/zero » has the major device number 1 and the minor device number 5. This is read/write accessible by anyone.

On the modern Linux system, the filesystem under » /dev/ » is automatically populated by the udev (7) mechanism.

1.2.11.В Special device files

There are some special device files.

TableВ 1.10.В List of special device files

	Caution

device file	action	description of response
/dev/null	read	return «end-of-file (EOF) character»
/dev/null	write	return nothing (a bottomless data dump pit)
/dev/zero	read	return «the \0 (NUL) character» (not the same as the number zero ASCII)
/dev/random	read	return random characters from a true random number generator, delivering real entropy (slow)
/dev/urandom	read	return random characters from a cryptographically secure pseudorandom number generator
/dev/full	write	return the disk-full (ENOSPC) error

These are frequently used in conjunction with the shell redirection (see Section 1.5.8, “Typical command sequences and shell redirection”).

1.2.12.В procfs and sysfs

The procfs and sysfs mounted on » /proc » and » /sys » are the pseudo-filesystem and expose internal data structures of the kernel to the userspace. In other word, these entries are virtual, meaning that they act as a convenient window into the operation of the operating system.

The directory » /proc » contains (among other things) one subdirectory for each process running on the system, which is named after the process ID (PID). System utilities that access process information, such as ps (1), get their information from this directory structure.

The directories under » /proc/sys/ » contain interfaces to change certain kernel parameters at run time. (You may do the same through the specialized sysctl (8) command or its preload/configuration file » /etc/sysctl.conf «.)

People frequently panic when they notice one file in particular — » /proc/kcore » — which is generally huge. This is (more or less) a copy of the content of your computer’s memory. It’s used to debug the kernel. It is a virtual file that points to computer memory, so don’t worry about its size.

The directory under » /sys » contains exported kernel data structures, their attributes, and their linkages between them. It also contains interfaces to change certain kernel parameters at run time.

See » proc.txt(.gz) «, » sysfs.txt(.gz) » and other related documents in the Linux kernel documentation (» /usr/share/doc/linux-doc-*/Documentation/filesystems/* «) provided by the linux-doc-* package.

1.2.13.В tmpfs

The tmpfs is a temporary filesystem which keeps all files in the virtual memory. The data of the tmpfs in the page cache on memory may be swapped out to the swap space on disk as needed.

The directory » /run » is mounted as the tmpfs in the early boot process. This enables writing to it even when the directory » / » is mounted as read-only. This is the new location for the storage of transient state files and replaces several locations described in the Filesystem Hierarchy Standard version 2.3:

» /var/lock » в†’ » /run/lock «

» /dev/shm » в†’ » /run/shm «

See » tmpfs.txt(.gz) » in the Linux kernel documentation (» /usr/share/doc/linux-doc-*/Documentation/filesystems/* «) provided by the linux-doc-* package.

1.3.В Midnight Commander (MC)

Midnight Commander (MC) is a GNU «Swiss army knife» for the Linux console and other terminal environments. This gives newbie a menu driven console experience which is much easier to learn than standard Unix commands.

You may need to install the Midnight Commander package which is titled » mc » by the following.

Use the mc (1) command to explore the Debian system. This is the best way to learn. Please explore few interesting locations just using the cursor keys and Enter key.

» /etc » and its subdirectories

» /var/log » and its subdirectories

» /usr/share/doc » and its subdirectories

1.3.1.В Customization of MC

In order to make MC to change working directory upon exit and cd to the directory, I suggest to modify «

/.bashrc » to include a script provided by the mc package.

See mc (1) (under the » -P » option) for the reason. (If you do not understand what exactly I am talking here, you can do this later.)

1.3.2.В Starting MC

MC can be started by the following.

MC takes care of all file operations through its menu, requiring minimal user effort. Just press F1 to get the help screen. You can play with MC just by pressing cursor-keys and function-keys.

In some consoles such as gnome-terminal (1), key strokes of function-keys may be stolen by the console program. You can disable these features in «Preferences» в†’ «General» and «Shortcuts» menu for gnome-terminal .

If you encounter character encoding problem which displays garbage characters, adding » -a » to MC’s command line may help prevent problems.

If this doesn’t clear up your display problems with MC, see SectionВ 9.5.6, “The terminal configuration”.

1.3.3.В File manager in MC

The default is two directory panels containing file lists. Another useful mode is to set the right window to «information» to see file access privilege information, etc. Following are some essential keystrokes. With the gpm (8) daemon running, one can use a mouse on Linux character consoles, too. (Make sure to press the shift-key to obtain the normal behavior of cut and paste in MC.)

TableВ 1.11.В The key bindings of MC

key	key binding
F1	help menu
F3	internal file viewer
F4	internal editor
F9	activate pull down menu
F10	exit Midnight Commander
Tab	move between two windows
Insert or Ctrl-T	mark file for a multiple-file operation such as copy
Del	delete file (be careful—set MC to safe delete mode)
Cursor keys	self-explanatory

1.3.4.В Command-line tricks in MC

cd command changes the directory shown on the selected screen.

Ctrl-Enter or Alt-Enter copies a filename to the command line. Use this with cp (1) and mv (1) commands together with command-line editing.

Alt-Tab shows shell filename expansion choices.

One can specify the starting directory for both windows as arguments to MC; for example, » mc /etc /root «.

Esc + n-key в†’ Fn (i.e., Esc + 1 в†’ F1 , etc.; Esc + 0 в†’ F10 )

Pressing Esc before the key has the same effect as pressing the Alt and the key together.; i.e., type Esc + c for Alt-C . Esc is called meta-key and sometimes noted as » M- «.

1.3.5.В The internal editor in MC

The internal editor has an interesting cut-and-paste scheme. Pressing F3 marks the start of a selection, a second F3 marks the end of selection and highlights the selection. Then you can move your cursor. If you press F6, the selected area is moved to the cursor location. If you press F5, the selected area is copied and inserted at the cursor location. F2 saves the file. F10 gets you out. Most cursor keys work intuitively.

This editor can be directly started on a file using one of the following commands.

This is not a multi-window editor, but one can use multiple Linux consoles to achieve the same effect. To copy between windows, use Alt-F n keys to switch virtual consoles and use «Fileв†’Insert file» or «Fileв†’Copy to file» to move a portion of a file to another file.

This internal editor can be replaced with any external editor of choice.

Also, many programs use the environment variables » $EDITOR » or » $VISUAL » to decide which editor to use. If you are uncomfortable with vim (1) or nano (1) initially, you may set these to » mcedit » by adding the following lines to «

I do recommend setting these to » vim » if possible.

If you are uncomfortable with vim (1), you can keep using mcedit (1) for most system maintenance tasks.

1.3.6.В The internal viewer in MC

MC is a very smart viewer. This is a great tool for searching words in documents. I always use this for files in the » /usr/share/doc » directory. This is the fastest way to browse through masses of Linux information. This viewer can be directly started using one of the following commands.

1.3.7.В Auto-start features of MC

Press Enter on a file, and the appropriate program handles the content of the file (see Section 9.4.11, “Customizing program to be started”). This is a very convenient MC feature.

TableВ 1.12.В The reaction to the enter key in MC

file type	reaction to enter key
executable file	execute command
man file	pipe content to viewer software
html file	pipe content to web browser
» *.tar.gz » and » *.deb » file	browse its contents as if subdirectory

In order to allow these viewer and virtual file features to function, viewable files should not be set as executable. Change their status using chmod (1) or via the MC file menu.

1.3.8.В FTP virtual filesystem of MC

MC can be used to access files over the Internet using FTP. Go to the menu by pressing F9 , then type » p » to activate the FTP virtual filesystem. Enter a URL in the form » username:passwd@hostname.domainname «, which retrieves a remote directory that appears like a local one.

Try «[deb.debian.org/debian]» as the URL and browse the Debian archive.

1.4.В The basic Unix-like work environment

Although MC enables you to do almost everything, it is very important for you to learn how to use the command line tools invoked from the shell prompt and become familiar with the Unix-like work environment.

1.4.1.В The login shell

You can select your login shell with chsh (1).

TableВ 1.13.В List of shell programs

package	popcon	size	POSIX shell	description
bash	V:796, I:999	6470	Yes	Bash: the GNU Bourne Again SHell (de facto standard)
bash-completion	V:31, I:922	1523	N/A	programmable completion for the bash shell
dash	V:913, I:993	221	Yes	Debian Almquist Shell, good for shell script
zsh	V:36, I:74	2467	Yes	Z shell: the standard shell with many enhancements
tcsh	V:8, I:28	1316	No	TENEX C Shell: an enhanced version of Berkeley csh
mksh	V:7, I:12	1478	Yes	A version of the Korn shell
csh	V:2, I:8	343	No	OpenBSD C Shell, a version of Berkeley csh
sash	V:0, I:6	1090	Yes	Stand-alone shell with builtin commands (Not meant for standard » /bin/sh «)
ksh	V:2, I:15	3284	Yes	the real, AT&T version of the Korn shell
rc	V:0, I:1	169	No	implementation of the AT&T Plan 9 rc shell
posh	V:0, I:0	190	Yes	Policy-compliant Ordinary SHell ( pdksh derivative)

Although POSIX-like shells share the basic syntax, they can differ in behavior for things as basic as shell variables and glob expansions. Please check their documentation for details.

In this tutorial chapter, the interactive shell always means bash .

1.4.2.В Customizing bash

You can customize bash (1) behavior by «

For example, try the following.

The bash-completion package enables programmable completion for bash .

1.4.3.В Special key strokes

In the Unix-like environment, there are few key strokes which have special meanings. Please note that on a normal Linux character console, only the left-hand Ctrl and Alt keys work as expected. Here are few notable key strokes to remember.

TableВ 1.14.В List of key bindings for bash

key	description of key binding
Ctrl-U	erase line before cursor
Ctrl-H	erase a character before cursor
Ctrl-D	terminate input (exit shell if you are using shell)
Ctrl-C	terminate a running program
Ctrl-Z	temporarily stop program by moving it to the background job
Ctrl-S	halt output to screen
Ctrl-Q	reactivate output to screen
Ctrl-Alt-Del	reboot/halt the system, see inittab (5)
Left-Alt-key (optionally, Windows-key )	meta-key for Emacs and the similar UI
Up-arrow	start command history search under bash
Ctrl-R	start incremental command history search under bash
Tab	complete input of the filename to the command line under bash
Ctrl-V Tab	input Tab without expansion to the command line under bash

The terminal feature of Ctrl-S can be disabled using stty (1).

1.4.4.В Mouse operations

Traditional Unix style mouse operations:

use 3 buttons (click)

used by X applications such as xterm and text applications in Linux console

Modern GUI style mouse operations:

use 2 buttons (drag + click)

use PRIMARY and CLIPBOARD

used in Modern GUI applications such as gnome-terminal

TableВ 1.15.В List of mouse operations and related key actions on Debian

action	response
Left-click-and-drag mouse	select range as PRIMARY selection
Left-click	select the start of range for PRIMARY selection
Right-click (traditional)	select the end of range for PRIMARY selection
Right-click (modern)	context dependent menu (cut/copy/paste)
Middle-click or Shift- Ins	insert PRIMARY selection at the cursor
Ctrl-X	cut PRIMARY selection to CLIPBOARD
Ctrl-C ( Shift-Ctrl-C in terminal)	copy PRIMARY selection to CLIPBOARD
Ctrl-V	paste CLIPBOARD at the cursor

Here, the PRIMARY selection is the highlighted text range. Within the terminal program, Shift-Ctrl-C is used instead to avoid terminating a running program.

The center wheel on the modern wheel mouse is considered middle mouse button and can be used for middle-click. Clicking left and right mouse buttons together serves as the middle-click under the 2 button mouse system situation.

In order to use a mouse in Linux character consoles, you need to have gpm (8) running as daemon.

1.4.5.В The pager

The less (1) command is the enhanced pager (file content browser). It reads the file specified by its command argument or its standard input. Hit » h » if you need help while browsing with the less command. It can do much more than more (1) and can be supercharged by executing » eval $(lesspipe) » or » eval $(lessfile) » in the shell startup script. See more in » /usr/share/doc/less/LESSOPEN «. The » -R » option allows raw character output and enables ANSI color escape sequences. See less (1).

1.4.6.В The text editor

You should become proficient in one of variants of Vim or Emacs programs which are popular in the Unix-like system.

I think getting used to Vim commands is the right thing to do, since Vi-editor is always there in the Linux/Unix world. (Actually, original vi or new nvi are programs you find everywhere. I chose Vim instead for newbie since it offers you help through F1 key while it is similar enough and more powerful.)

If you chose either Emacs or XEmacs instead as your choice of the editor, that is another good choice indeed, particularly for programming. Emacs has a plethora of other features as well, including functioning as a newsreader, directory editor, mail program, etc. When used for programming or editing shell scripts, it intelligently recognizes the format of what you are working on, and tries to provide assistance. Some people maintain that the only program they need on Linux is Emacs. Ten minutes learning Emacs now can save hours later. Having the GNU Emacs manual for reference when learning Emacs is highly recommended.

All these programs usually come with tutoring program for you to learn them by practice. Start Vim by typing » vim » and press F1-key. You should at least read the first 35 lines. Then do the online training course by moving cursor to » |tutor| » and pressing Ctrl-] .

Good editors, such as Vim and Emacs, can handle UTF-8 and other exotic encoding texts correctly. It is a good idea to use the GUI environment in the UTF-8 locale and to install required programs and fonts to it. Editors have options to set the file encoding independent of the GUI environment. Please refer to their documentation on multibyte text.

1.4.7.В Setting a default text editor

Debian comes with a number of different editors. We recommend to install the vim package, as mentioned above.

Debian provides unified access to the system default editor via command » /usr/bin/editor » so other programs (e.g., reportbug (1)) can invoke it. You can change it by the following.

The choice » /usr/bin/vim.basic » over » /usr/bin/vim.tiny » is my recommendation for newbies since it supports syntax highlighting.

Many programs use the environment variables » $EDITOR » or » $VISUAL » to decide which editor to use (see SectionВ 1.3.5, “The internal editor in MC” and SectionВ 9.4.11, “Customizing program to be started”). For the consistency on the Debian system, set these to » /usr/bin/editor «. (Historically, » $EDITOR » was » ed » and » $VISUAL » was » vi «.)

1.4.8.В Using vim

The recent vim (1) starts itself in the sane » nocompatible » option and enters into the NORMAL mode. [1]

TableВ 1.16.В List of basic Vim key strokes

mode	key strokes	action
NORMAL	:help|only	display the help file
NORMAL	:e filename.ext	open new buffer to edit filename.ext
NORMAL	:w	overwrite current buffer to the original file
NORMAL	:w filename.ext	write current buffer to filename.ext
NORMAL	:q	quit vim
NORMAL	:q!	force to quit vim
NORMAL	:only	close all other split open windows
NORMAL	:set nocompatible?	check if vim is in the sane nocompatible mode
NORMAL	:set nocompatible	set vim to the sane nocompatible mode
NORMAL	i	enter the INSERT mode
NORMAL	R	enter the REPLACE mode
NORMAL	v	enter the VISUAL mode
NORMAL	V	enter the linewise VISUAL mode
NORMAL	Ctrl- V	enter the blockwise VISUAL mode
except TERMINAL-JOB	ESC -key	enter the NORMAL mode
NORMAL	:term	enter the TERMINAL-JOB mode
TERMINAL-NORMAL	i	enter the TERMINAL-JOB mode
TERMINAL-JOB	Ctrl- W N (or Ctrl- \ Ctrl- N )	enter the TERMINAL-NORMAL mode
TERMINAL-JOB	Ctrl- W :	enter the Ex -mode in TERMINAL-NORMAL mode

Please use the » vimtutor » program to learn vim through an interactive tutorial course.

The vim program changes its behavior to typed key strokes based on mode . Typing in key strokes to the buffer is mostly done in INSERT -mode and REPLACE -mode. Moving cursor is mostly done in NORMAL -mode. Interactive selection is done in VISUAL -mode. Typing » : » in NORMAL -mode changes its mode to Ex -mode. Ex -mode accepts commands.

The Vim comes with the Netrw package. Netrw supports reading files, writing files, browsing directories over a network, and local browsing! Try Netrw with » vim . » (a period as the argument) and read its manual at » :help netrw «.

For the advanced configuration of vim , see Section 9.2, “Customizing vim”.

1.4.9.В Recording the shell activities

The output of the shell command may roll off your screen and may be lost forever. It is a good practice to log shell activities into the file for you to review them later. This kind of record is essential when you perform any system administration tasks.

The new Vim (version>=8.2) can be used to record the shell activities cleanly using TERMINAL-JOB -mode. See Section 1.4.8, “Using vim”.

The basic method of recording the shell activity is to run it under script (1).

For example, try the following

Do whatever shell commands under script .

Press Ctrl-D to exit script .

1.4.10.В Basic Unix commands

Let’s learn basic Unix commands. Here I use «Unix» in its generic sense. Any Unix clone OSs usually offer equivalent commands. The Debian system is no exception. Do not worry if some commands do not work as you wish now. If alias is used in the shell, its corresponding command outputs are different. These examples are not meant to be executed in this order.

Try all following commands from the non-privileged user account.

TableВ 1.17.В List of basic Unix commands

command	description
pwd	display name of current/working directory
whoami	display current user name
id	display current user identity (name, uid, gid, and associated groups)
file foo	display a type of file for the file » foo «
type -p commandname	display a file location of command » commandname «
which commandname	, ,
type commandname	display information on command » commandname «
apropos key-word	find commands related to » key-word «
man -k key-word	, ,
whatis commandname	display one line explanation on command » commandname «
man -a commandname	display explanation on command » commandname » (Unix style)
info commandname	display rather long explanation on command » commandname » (GNU style)
ls	list contents of directory (non-dot files and directories)
ls -a	list contents of directory (all files and directories)
ls -A	list contents of directory (almost all files and directories, i.e., skip » .. » and » . «)
ls -la	list all contents of directory with detail information
ls -lai	list all contents of directory with inode number and detail information
ls -d	list all directories under the current directory
tree	display file tree contents
lsof foo	list open status of file » foo «
lsof -p pid	list files opened by the process ID: » pid «
mkdir foo	make a new directory » foo » in the current directory
rmdir foo	remove a directory » foo » in the current directory
cd foo	change directory to the directory » foo » in the current directory or in the directory listed in the variable » $CDPATH «
cd /	change directory to the root directory
cd	change directory to the current user’s home directory
cd / foo	change directory to the absolute path directory » / foo «
cd ..	change directory to the parent directory
cd

foo change directory to the home directory of the user » foo « cd — change directory to the previous directory display contents of » /etc/motd » using the default pager touch junkfile create a empty file » junkfile « cp foo bar copy a existing file » foo » to a new file » bar « rm junkfile remove a file » junkfile « mv foo bar rename an existing file » foo » to a new name » bar » (» bar » must not exist) mv foo bar move an existing file » foo » to a new location » bar / foo » (the directory » bar » must exist) mv foo bar / baz move an existing file » foo » to a new location with a new name » bar / baz » (the directory » bar » must exist but the directory » bar / baz » must not exist) chmod 600 foo make an existing file » foo » to be non-readable and non-writable by the other people (non-executable for all) chmod 644 foo make an existing file » foo » to be readable but non-writable by the other people (non-executable for all) chmod 755 foo make an existing file » foo » to be readable but non-writable by the other people (executable for all) find . -name pattern find matching filenames using shell » pattern » (slower) locate -d . pattern find matching filenames using shell » pattern » (quicker using regularly generated database) grep -e » pattern » *.html find a » pattern » in all files ending with » .html » in current directory and display them all top display process information using full screen, type » q » to quit ps aux | pager display information on all the running processes using BSD style output ps -ef | pager display information on all the running processes using Unix system-V style output ps aux | grep -e «[e]xim4*» display all processes running » exim » and » exim4 « ps axf | pager display information on all the running processes with ASCII art output kill 1234 kill a process identified by the process ID: » 1234 « gzip foo compress » foo » to create » foo .gz » using the Lempel-Ziv coding (LZ77) gunzip foo .gz decompress » foo .gz » to create » foo « bzip2 foo compress » foo » to create » foo .bz2 » using the Burrows-Wheeler block sorting text compression algorithm, and Huffman coding (better compression than gzip ) bunzip2 foo .bz2 decompress » foo .bz2 » to create » foo « xz foo compress » foo » to create » foo .xz » using the Lempel–Ziv–Markov chain algorithm (better compression than bzip2 ) unxz foo .xz decompress » foo .xz » to create » foo « tar -xvf foo .tar extract files from » foo .tar » archive tar -xvzf foo .tar.gz extract files from gzipped » foo .tar.gz » archive tar -xvjf foo .tar.bz2 extract files from » foo .tar.bz2 » archive tar -xvJf foo .tar.xz extract files from » foo .tar.xz » archive tar -cvf foo .tar bar / archive contents of folder » bar / » in » foo .tar » archive tar -cvzf foo .tar.gz bar / archive contents of folder » bar / » in compressed » foo .tar.gz » archive tar -cvjf foo .tar.bz2 bar / archive contents of folder » bar / » in » foo .tar.bz2 » archive tar -cvJf foo .tar.xz bar / archive contents of folder » bar / » in » foo .tar.xz » archive zcat README.gz | pager display contents of compressed » README.gz » using the default pager zcat README.gz > foo create a file » foo » with the decompressed content of » README.gz « zcat README.gz >> foo append the decompressed content of » README.gz » to the end of the file » foo » (if it does not exist, create it first)

Unix has a tradition to hide filenames which start with » . «. They are traditionally files that contain configuration information and user preferences.

For cd command, see builtins (7).

The default pager of the bare bone Debian system is more (1) which cannot scroll back. By installing the less package using command line » apt-get install less «, less (1) becomes default pager and you can scroll back with cursor keys.

The » [ » and » ] » in the regular expression of the » ps aux | grep -e «[e]xim4*» » command above enable grep to avoid matching itself. The » 4* » in the regular expression means 0 or more repeats of character » 4 » thus enables grep to match both » exim » and » exim4 «. Although » * » is used in the shell filename glob and the regular expression, their meanings are different. Learn the regular expression from grep (1).

Please traverse directories and peek into the system using the above commands as training. If you have questions on any of console commands, please make sure to read the manual page.

For example, try the following

The style of man pages may be a little hard to get used to, because they are rather terse, particularly the older, very traditional ones. But once you get used to it, you come to appreciate their succinctness.

Please note that many Unix-like commands including ones from GNU and BSD display brief help information if you invoke them in one of the following ways (or without any arguments in some cases).

1.5.В The simple shell command

Now you have some feel on how to use the Debian system. Let’s look deep into the mechanism of the command execution in the Debian system. Here, I have simplified reality for the newbie. See bash (1) for the exact explanation.

A simple command is a sequence of components.

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