Objectives

In this lab, you will become familiar with Linux command line text editors and configuration files. Part 1: Graphical Text Editors

Part 2: Command Line Text Editors

Part 3: Working with Configuration Files

Instructions Part 1: Graphical Text Editors

Before you can work with text files in Linux, you must be familiar with text editors.

Text editors are one of the oldest categories of applications created for computers. Linux, like many other operating systems, has many different text editors, with various features and functions. Some text editors include graphical interfaces, while others are only usable via the command line. Each text editor includes a feature set designed to support a specific work scenario. Some text editors focus on the programmer and include features such as syntax highlighting, bracket matching, find and replace, multi-line Regex support, spell check, and other programming-focused features.

To save space and keep the virtual machine lean, the Cisco CyberOps Workstation VM only includes SciTE as a graphical text editor application. SciTE is a simple, small and fast text editor. It does not have many advanced features, but it fully supports the work done in this course.

Note: The choice of text editor is a personal one. There is no such thing as a best text editor. The best text editor is the one that you feel most comfortable with and works best for you.

Step 1: Open SciTE from the GUI

Step 2: Open SciTE from the Terminal.

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Part 2: Command Line Text Editors

While graphical text editors are convenient and easy to use, command line-based text editors are very important in Linux computers. The main benefit of command line-based text editors is that they allow for text file editing from a remote shell on a remote computer.

Consider the following scenario. A user must perform administrative tasks on a Linux computer but is not sitting in front of that computer. Using SSH, the user starts a remote shell to the aforementioned computer. Under the text-based remote shell, the graphical interface may not be available which makes it impossible to rely on graphical text editors. In this type of situation, text-based text editors are crucial.

Note: This is mainly true when connecting to remote, headless servers that lack a GUI interface.

The Workstation VM includes a few command line-based text editors. This course focuses on nano.

Note: Another extremely popular text editor is called vi. While the learning curve for vi is considered steep, vi is a very powerful command line-based text editor. It is included by default in almost all Linux distributions and its original code was first created in 1976. An updated version of vi is named vim which stands for viimproved. Today most vi users are actually using the updated version, vim.

Due to the lack of graphical support, nano (or GNU nano) can be controlled solely through the keyboard.

CTRL+O saves the current file; CTRL+W opens the search menu. GNU nano uses a two-line shortcut bar at the bottom of the screen, where a number of commands for the current context are listed. After nano is open, press CTRL+G for the help screen and a complete list.

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Part 3: Working with Configuration Files

In Linux, everything is treated as a file, including the memory, the disks, the monitor output, the files, and the directories. From the operating system standpoint, everything is a file. It should be no surprise that the system itself is configured through files. Known as configuration files, they are usually text files and are used by various applications and services to store adjustments and settings for that specific application or service. Practically everything in Linux relies on configuration files to work. Some services have not one but several configuration files.

Users with proper permission levels use text editors to change the contents of such configuration files. After the changes are made, the file is saved and can be used by the related service or application. Users are able to specify exactly how they want any given application or service to behave. When launched, services and applications check the contents of specific configuration files and adjust their behavior accordingly.

Step 1: Locating Configuration Files

The program author defines the location of configuration for a given program (service or application). Because of that, the documentation should be consulted when assessing the location of the configuration file. Conventionally however, in Linux, configuration files that are used to configure user applications are often placed in the user’s home directory while configuration files used to control system-wide services are placed in the /etc directory. Users always have permission to write to their own home directories and are able to configure the behavior of applications they use.

c. Use cat command to display the contents of the .bashrc file. This file is used to configure user-specific terminal behavior and customization.

[analyst@secOps ~]$ cat .bashrc export EDITOR=vim

PS1=’\[\e[1;32m\][\u@\h \W]\$\[\e[0m\] ‘ alias ls=”ls –color” alias vi=”vim”

Do not worry too much about the syntax of .bashrc at this point. The important thing to notice is that .bashrc contains configuration for the terminal. For example, the line PS1=’\[\e[1;32m\][\u@\h \W]\$\[\e[0m\] ‘ defines the prompt structure of the prompt displayed by the terminal:

[username@hostname current_dir] followed by a dollar sign, all in green. A few other configurations include shortcuts to commands such as ls and vi. In this case, every time the user types ls, the shell automatically converts that to ls –color to display a color-coded output for ls (directories in blue, regular files in grey, executable files in green, etc.)

The specific syntax is out of the scope of this course. What is important is understanding that user configurations are conventionally stored as hidden files in the user’s home directory.

d.  While configuration files related to user applications are conventionally placed under the user’s home directory, configuration files relating to system-wide services are place in the /etc directory, by convention. Web services, print services, ftp services, and email services are examples of services that affect the entire system and of which configuration files are stored under /etc. Notice that regular users do not have writing access to /etc. This is important as it restricts the ability to change the system-wide service configuration to the root user only.

Use the ls command to list the contents of the /etc directory:

[analyst@secOps ~]$ ls /etc adjtime host.conf mke2fs.conf rc_maps.cfg apache-ant hostname mkinitcpio.conf request-key.conf apparmor.d hosts mkinitcpio.d request-key.d arch-release ifplugd modprobe.d resolv.conf avahi initcpio modules-load.d resolvconf.conf bash.bash_logout inputrc motd rpc bash.bashrc iproute2 mtab rsyslog.conf binfmt.d iptables nanorc securetty ca-certificates issue netconfig security crypttab java-7-openjdk netctl services

dbus-1 java-8-openjdk netsniff-ng shadow default kernel nginx shadowdepmod.d krb5.conf nscd.conf shells dhcpcd.conf ld.so.cache nsswitch.conf skel dhcpcd.duid ld.so.conf ntp.conf ssh dkms ld.so.conf.d openldap ssl drirc libnl openvswitch sudoers elasticsearch libpaper.d os-release  sudoers.d environment lightdm pacman.conf sudoers.pacnew ethertypes locale.conf pacman.conf.pacnew sysctl.d filebeat locale.gen pacman.d systemd fonts locale.gen.pacnew pam.d tmpfiles.d fstab localtime pango trusted-key.key gai.conf login.defs papersize udev gemrc logrotate.conf passwd UPower group logrotate.d passwd-  vdpau_wrapper.cfg group-  logstash pcmcia vimrc

group.pacnew lvm pkcs11 webapps grub.d machine-id polkit-1 wgetrc gshadow  mail.rc profile X11 gshadow-  makepkg.conf profile.d xdg gshadow.pacnew man_db.conf protocols xinetd.d gtk-2.0 mdadm.conf pulse yaourtrc gtk-3.0  mime.types rc_keymaps

  e.  Use the cat command to display the contents of the bash.bashrc file:

[analyst@secOps ~]$ cat /etc/bash.bashrc

#

# /etc/bash.bashrc

#

# If not running interactively, don’t do anything

[[ $- != *i* ]] && return

[[ $DISPLAY ]] && shopt -s checkwinsize PS1='[\u@\h \W]\$ ‘

case ${TERM} in

xterm*|rxvt*|Eterm|aterm|kterm|gnome*)

PROMPT_COMMAND=${PROMPT_COMMAND:+$PROMPT_COMMAND; }’printf “\033]0;%s@%s:%s\007”

“${USER}” “${HOSTNAME%%.*}” “${PWD/#$HOME/\~}”‘

;; screen)

PROMPT_COMMAND=${PROMPT_COMMAND:+$PROMPT_COMMAND; }’printf “\033_%s@%s:%s\033\\”

“${USER}” “${HOSTNAME%%.*}” “${PWD/#$HOME/\~}”‘

;; esac

[ -r /usr/share/bash-completion/bash_completion ] && . /usr/share/bashcompletion/bash_completion

[analyst@secOps ~]$

The syntax of bash.bashrc is out of scope of this course. This file defines the default behavior of the shell for all users. If a user wants to customize his/her own shell behavior, the default behavior can be overridden by editing the .bashrc file located in the user’s home directory. Because this is a system-wide configuration, the configuration file is placed under /etc, making it editable only by the root user.

Therefore, the user will have to log in as root to modify bash.bashrc.

Question:

Why are user application configuration files saved in the user’s home directory and not under /etc with all the other system-wide configuration files? User application configuration files are save in the users home directory rather than under /etc to ensure user specific settings, proper permissions, isolation, and security and easy portability. This setup allows individual customization, prevent unauthorized access to system-wide settings, and simplifies the transfer of user environments.,

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Step 2: Editing and Saving Configuration files

As mentioned before, configuration files can be edited with text editors.

Let’s edit .bashrc to change the color of the shell prompt from green to red for the analyst user.

The terminal window that was already open will not change its prompt color from green to red immediately

after saving and closing the SciTE file. The reason is that the changes in the .bashrc file take effect only when

a new terminal session is started.

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[ Read 5 lines ]

  ^G Get Help ^O Write Out ^W Where Is ^K Cut Text ^J Justify  ^C Cur Pos

  ^X Exit  ^R Read File ^\ Replace  ^U Uncut Text^T To Spell ^_ Go To Line

Step 3: Editing Configuration Files for Services

System-wide configuration files are not very different from the user-application files. nginx is a lightweight web server that is installed in the CyberOPS Workstation VM. nginx can be customized by changing its configuration file, which is located in /etc/nginx.

a.  First, open nginx’s configuration file in a nano. The configuration file name used here is custom_server.conf. Notice below that the command is preceded by the sudo command. After typing nano include a space and the -l switch. If prompted for a password, enter cyberops.

[analyst@secOps ~]$ sudo nano -l /etc/nginx/custom_server.conf [sudo] password for analyst:

Use the arrow keys to navigate through the file.

  GNU nano 4.9.2  /etc/nginx/custom_server.conf

1

4

8

9 #pid logs/nginx.pid;

10

11

15

16

20

25 #access_log logs/access.log main;

26

27 sendfile on; 28 #tcp_nopush on;

29

30 #keepalive_timeout 0; 31 keepalive_timeout 65;

32

33 #gzip on;

34

37

41

42 #charset koi8-r;

43

44 #access_log logs/host.access.log main;

45

<Some output omitted>

Note: Conventionally, .conf extensions are used to identify configuration files.

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Challenge Question: Can you edit the /etc/nginx/custom_configuration.conf file with SciTE?

Describe the process below.

Remember, because the file is stored under /etc, you will need root permissions to edit it. From a terminal window, issue sudo scite /etc/nginx/custom_configuration.conf to launch scite as root.

Reflection

Depending on the service, more options may be available for configuration.

Configuration file location, syntax, and available parameters will vary from service to service. Always consult the documentation for information.

Permissions are a very common cause of problems. Make sure you have the correct permissions before trying to edit configuration files.

More often than not, services must be restarted before the changes take effect.

End of document

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