Chapter 1-3 Commands

Which permission operator grants permissions

+

Which permission operator denies permissions

-

This file provides system wide environment variables. This is more effective for administrators to configure if there are settings to apply for all users. The system reads on initial login this file first, then the .profile file, and the .profile file is read every time a new shell is run, while the "answer to this question" file is only run at login.

/etc/profile

This directory servers as a storage location for scripts administrators may use to set addition system-wide variables.

/etc/profile.d/

A storage location for hashed passwords as well as additional information only the root has access to

/etc/shadow

The contents of this directory are automatically copied into the home directories of new users. Administrators can pre-load this directory with configuration files or other content. When the useradd command is run, this directory is copied into the new user's home, giving the new user access to the configurations they might need.

/etc/skel/

Directory that contains documents for libraries, system utilities, and other software packages installed on the system.

/usr/share/doc/

Create user accounts and configure basic settings.

useradd

View the default configuration for new users

useradd -D

Sets the comment field for an account, which is usually the user's full name

useradd -c "Example Name" example

Searches the name section of all man pages for the keyword that the user provides. Useful for finding a command when you don't know its name but rather its function

apropos

Displays history of user login and logout actions, along with the time of which they have done so

last

View contents of a file when those contents won't fit entirely on the screen

less

Lists the contents of a directory.

ls

Lists contents of directory and shows hidden files

ls -a

Lists contents of directory in long format

ls -l

Shows the current directory you're in

pwd

Which permission attribute represents the ability to access and view contents of a file, and ability to list contents of a directory

r

reboots the system without using the shutdown command

reboot

shuts down the system in 90 seconds

shutdown -h -t 90

Shuts down the system with no delay

shutdown -h now

reboots the system with no time delay using the shutdown command

shutdown -r now

Pauses system activities for 60 seconds

sleep 60

Which command enables a user to log in to a system with their own credentials, and then to become the root user to perform administrative tasks?

su

Switch the user to root user

su - root

A fellow administrator calls you and needs you to check the /etc/shadow file for a new user's entry, confirming that it indeed exists. How would you look at the contents of the /etc/shadow file without the possibility of changing the file?

su -root, cat /etc/shadow

Any user who knows the root password can get root permissions using this command without substituting for the root user

sudo

Command that enables a user to edit a file with their own credentials even if the file is only accessible to the root user

sudoedit

To use the sudoedit command under a given user, you must make an edit to which file?

sudoers

Updates the timestamp on a file that exists or creates a new file

touch

You need to quickly create an empty file (log.txt) so that an application can copy data into it. Which command can you use to create the file?

touch log.txt

The first character in the ls -l command represents the

type of object

Which permission context represents the owner or user of a file or directory

u

Sets an accounts expiration date

useradd -e exampledate

Sets a user's default shell

useradd -s /bin/ksh

Three commands that are used to edit the /etc/passwd file

useradd usermod userdel

Starts the defualt editor for linux

vim

A command that allows the system to verify the syntax of the /etc/sudoers file before committing changes, which allows you to correct a mistake before they become a part of the configuration

visudo

What command is used to edit the privileges' of the wheel group

visudo

Checks the existing sudoers file for errors

visudo -c

Edit or check a sudoers file in a different location than the default location

visudo -f example

Check the sudoers file in strict mode, any aliases that are used before being defined will result in errors

visudo -s

Output the sudoers file to the specified file in javascript object notation or JSON format

visudo -x example

Displays details of users who are currently logged in to a system and their transactions

w

Which permission attribute represents the ability to save changes to a file or create, rename, and delete files in a directory (also requires the execute attribute to also be set)

w

Display a brief description of a given command including commands that appear in multiple sections. The opposite of apropos, for when you know the name but not what it does

whatis

A group that can exercise administrative privileges of the root user with less potential damage to the system. These users can use the sudo command without logging into the root account

wheel

Determine the details of who is logged into the system.

who

See how long users have been idle logged into a machine

who -u

Displays the username you are currently logged into the system as

whoami

Which permission attribute represents the ability to run a script, program, or other software file and access a directory, execute a file from that directory, or perform a task on that directory like a search

x

Which permission context represents the file or directory's group and all users belonging to that group

g

A file storage location for groups, all groups will be found on this file

/etc/group

A file that stores user account information.

/etc/passwd

the fifth block or number 11 in the ls -l command represents the ( period for SELinux security context and plus for any other combination of alternative access methods)

access method

Starts a GUI text editor that is easy to use that also requires a desktop enviroment

gedit

Displays a quick summary of usage of a command and a list of arguments that can be used.

--help

Shell configuration file for the initial login environment. This file is only read with the first login.

.bash_profile

A file that enables customization of the user's environment, for example the use of aliases for abbreviated commands. This enables them to not impact other users while enhancing their experience. (username, system hostname, current directory, defualt directory, and file permissions are also stored here)

.bashrc

This file allows for user customization and is read by the system every time a new shell is opened.

.profile

This file provides you with system wide bash settings, which differs from the /etc/profile file which is for variables.

/etc/bashrc

Which permission context represents all three permission attribute contexts?

a

View contents of a file without the option to edit the file

cat

Changes your working directory

cd

The command that enables you to modify the permissions of a file or directory. Only the owner of the file or directory or sysadmin can change the permissions of the object

chmod

Modify permissions of files and directories recursively

chmod -R

Report changes that are mode in permissions

chmod -c

Hide most error messages when modifying permissions of a file or directory

chmod -f

Display a diagnostic entry for every file processed while modifying file permissions

chmod -v

Empty the screen of previous commands to eliminate distracting information

clear

Bash syntax

command -options arguments

Copies a file or directory to another location

cp

Repeats input back to the user on the screen. Commonly used to send information to the user in a script

echo

the third block or numbers 5-7 of the ls -l command represent the

group permissions

The command that creates a group

groupadd

Exists with success if the group already exists

groupadd -f groupname

Assigns an ID to a group

groupadd -g 1234 groupname

Allows a group to be created with a non-unique group ID

groupadd -o -g groupname

Commands to properly edit the /etc/group file

groupadd groupmod groupdel

Delete a group from the /etc/group file. It doesn't delete the user accounts in the group

groupdel

Command to change a group's own attributes

groupmod

Change the group ID

groupmod -g 123 groupname

Rename a group

groupmod -n newgroupname oldgroupname

Shows most recently entered commands

history

Displays user ID and group ID information. You can specify a user name as an option to display ID information about a specific user.

id

Displays the info page of a command, which are alternatives to the man pages and favored by GNU project.

info

Lists contents of a specific directory

ls /example/

Understand a command using a command without using the internet

man

Displays debugging information for a command

man -D

Searches for a specified string on all man pages

man -K

Find all man pages matching a query

man -a

Displays a short description of a command along with the man page

man -f

Displays help options for a man command

man -h

Lists all manual pages containing the keyword along with their location

man -k

Makes a new directory

mkdir

Simplier user friendly text editor

nano

Which permission context represents all other users who are not users/owners or group members

o

the fourth block or numbers 8-10 in the ls -l command represent the

other permissions

the second block or numbers 2-4 in the ls -l command represent the

owner permissions

A command used by root to set or reset a password for any user. A user can also reset their own password. Use this after the useradd command

passwd