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RHEL7 Boot Process Step by Step Explained - Tech Arkit

RHEL7 - RHCSA Red Hat Certified System Administrator the first certification for beginners to earn.

A. Understand and use essential tools

1. Access a shell prompt and issue commands with correct syntax

2. Use input-output redirection (>, >>, |, 2>, etc.)

3. Use grep and regular expressions to analyze text

4. Access remote systems using ssh

5. Log in and switch users in multiuser targets

6. Archive, compress, unpack, and uncompress files using tar, star, gzip, and bzip2

7. Create and edit text files

8. Create, delete, copy, and move files and directories

9. Create hard and soft links

10. List, set, and change standard ugo/rwx permissions

11. Locate, read, and use system documentation including man, info, and files in /usr/share/doc

B. Operate running systems

12. Boot, reboot, and shut down a system normally

13. Boot systems into different targets manually

14. Interrupt the boot process in order to gain access to a system

15. Identify CPU/memory intensive processes, adjust process priority with renice, and kill processes

16. Locate and interpret system log files and journals

17. Access a virtual machine's console

18. Start and stop virtual machines

19. Start, stop, and check the status of network services

20. Securely transfer files between systems

C. Configure local storage

21. List, create, delete partitions on MBR and GPT disks

22. Create and remove physical volumes, assign physical volumes to volume groups, and create and delete logical volumes

23. Configure systems to mount file systems at boot by Universally Unique ID (UUID) or label

24. Add new partitions and logical volumes, and swap to a system non-destructively

D. Create and configure file systems

25. Create, mount, unmount, and use vfat, ext4, and xfs file systems

26. Mount and unmount CIFS and NFS network file systems

27. Extend existing logical volumes

28. Create and configure set-GID directories for collaboration

29. Create and manage Access Control Lists (ACLs)

30. Diagnose and correct file permission problems

E. Deploy, configure, and maintain systems

31. Configure networking and hostname resolution statically or dynamically

32. Schedule tasks using at and cron

33. Start and stop services and configure services to start automatically at boot

34. Configure systems to boot into a specific target automatically

35. Install Red Hat Enterprise Linux systems as virtual guests

36. Configure systems to launch virtual machines at boot

37. Configure network services to start automatically at boot

38. Configure a system to use time services

40. Install and update software packages from Red Hat Network, a remote repository, or from the local file system

41. Update the kernel package appropriately to ensure a bootable system

42. Modify the system bootloader

F. Manage users and groups

43. Create, delete, and modify local user accounts

44. Change passwords and adjust password aging for local user accounts

45. Create, delete, and modify local groups and group memberships

46. Configure a system to use an existing authentication service for user and group information

G. Manage security

47. Configure firewall settings using firewall-config, firewall-cmd, or iptables

48. Configure key-based authentication for SSH

49. Set enforcing and permissive modes for SELinux

50. List and identify SELinux file and process context

51. Restore default file contexts

52. Use boolean settings to modify system SELinux settings

53. Diagnose and address routine SELinux policy violations

Edit configuration files faster ever using vi and vim RHCSA

______________________

Text Editores

______________________

Syntax: vi <FileName>

#vi FileName

Insert Mode: You can able to Insert/Write the Data to the Text file.

Command Mode: You can able to copy the text/Delete the text Paste.

EX-Mode: Execute commands, Write/Exit

-------------------------

Command Mode shortcut

-------------------------

command mode is default mode to execute text manupalation commands

dd = Delete Line

d5d - will delete 5 lines

5dd - will delete lines

x = Delete Character

nx - delete n characters (Ex. 6x deletes SIX characters)

yy = copy line

y6y - it will copy SIX lines to below

6yy - it will copy SIX lines to below

p = Paste copied lines below the cursor

P = Paste copied line above the cursor

dw = delete single word

u - undo the last action

J - join the line

. - redo

U - undo all changes to the current Line

w - will move to the begining of the next word

nw - will move to nth word begning

b - will move begining of the previous word

nb - will move begining of nth previous words

{ - move backword one paragraph

} - move forward one paragraph

0 - will go to home position

$ - will go to end of the line position

h <-- using h key we can go from right to left direction

l --> using l key we can go from left to right direction

k ^ using k key we can go UP from down

j -- Using j key we can go Down from UP

Shift +G == go to Last line of the file

Shift+h == go to first line of screen

Shift+z == Save & Quit

n = Search Strings from top to bottom

N = Search from bottom to top

%s/Old/New == Replace content from old to new

/StringName == Search Particular Word in the file.

-----------------

Insert Mode

-----------------

i = Insert Data before the cursor position

I = Insert content starting of the Line

a = It will append current Line characters

A = It will append the characters from end of the Line

o = It will insert a new line below the cursor

O = It will insert a new line above the cursor

s = substitute the stream

r = replace the current character

'home' key to go home of the line

'end' key to go end of the line

------------------

Ex-Mode Shortcut

------------------

Esc key to change the mode to Execute mode

:q = Quit file

:w = write file

:wq = Save& quit.

:q! = quit forcefully

:wq! = Save & Exit forcefully

:1 == go to first line of the File

:set nu == Set the line numbers

:set nonu == Remove Line numbers

:<spesify line number> == Specified Line number.

:r /root/test = copy the content of test file in cursor current position

:r !date = the command output will paste in current cursor position

____________________________

nano Text Editor

____________________________

CTRL+g Or F1 = Help

CTRL+x Or F2 = Save File

CTRL+o Or F3 = Write to file to disk

CTRL+j Or F4 = To justify

CTRL+r Or F5 = To insert file text to cursor current position

CTRL+w Or F6 = Search for string

CTRL+y Or F7 = Move to previous screen

CTRL+v Or F8 = Move to the Next Screen

CTRL+k Or F9 = Cut the current and keep into buffer

CTRL+v Or F10 = Uncut/Paste into current file

CTRL+c Or F11 = Display the position of the cursor

CTRL+SHIFT+G = Go to mentioned Line

nmtui Text Based User Interface RHEL 7 - RHCSA - Tech Arkit

nmtui - NetworkManager-tui Text User Interface for controlling NetworkManager

rpm -qa |grep NetworkManager-tui

nmtui edit connection_name

nmtui connect connection_name

nmtui-edit | nmtui edit {name | id}

nmtui-connect | nmtui connect {name | uuid | device | SSID}

nmtui-hostname | nmtui hostname

nmtui is a curses based TUI application for interacting with NetworkManager.When starting nmtui, the user is prompted to choose the activity to perform unless it was specified as the first argument.

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nmcli command-line tool for controlling NetworkManager - RHEL 7 - RHCSA

nmcli is a command-line tool for controlling NetworkManager and reporting network status. It can be utilized as a replacement for nm-applet or other graphical clients. nmcli is used to create, display, edit, delete, activate, and deactivate network connections, as well as control and display network device status.

Scripts: Utilize NetworkManager via nmcli instead of managing network connections manually. nmcli supports a terse output format which is better suited for script processing. Note that NetworkManager can also execute scripts, called "dispatcher scripts", in response to network events. See NetworkManager(8) for details about these dispatcher scripts.

Servers, headless machines, and terminals: nmcli can be used to control NetworkManager without a GUI, including creating, editing, starting and stopping network connections and viewing network status.

NetworkManager stores all network configuration as "connections", which are collections of data (Layer2 details, IP addressing, etc.) that describe how to create or connect to a network. A connection is "active" when a device uses that connection's configuration to create or connect to a network. There may be multiple connections that apply to a device, but only one of them can be active on that device at any given time. The additional connections can be used to allow quick switching between different networks and configurations.

Consider a machine which is usually connected to a DHCP-enabled network, but sometimes connected to a testing network which uses static IP addressing. Instead of manually reconfiguring eth0 each time the network is changed, the settings can be saved as two connections which both apply to eth0, one for DHCP (called default) and one with the static addressing details (called testing). When connected to the DHCP-enabled network the user would run nmcli con up default , and when connected to the static network the user would run nmcli con up testing.

nmcli monitor

nmcli connection {show | up | down | modify | add | edit | clone | delete | monitor | reload | load | import | export} [ARGUMENTS...]

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13 Regular Expression with Grep Command RHCSA - Tech Arkit

1. Check Grep version

grep -V

2. Search single word in single file / multifles

grep string *

3. Search Multiple words in single file / multiple files

grep -E 'word1|word2'

4. Seach text which is not maching to string

grep -v "String" fileName

5. Print the matching string and its before lines

grep ens33 -A 4

6. Print the matching string and its after lines and its around lines

grep enss33 -B 4

grep ens33 -C 4

7. Search a string Recursively

grep -r string fileName

8. Grep the string with highlighted in color

grep --color=auto string file Name

export GREP_COLOR='1;30;43'

9. display the lines which does not matches all the given strings

grep -v -e "a" -e "b" -e "c" filename.txt

10. Get the count of given string from file

grep -c string filename

11. Search for files which are matching to the given string

grep -l this demo*

12. Beginning of line ^ using cap symble

grep "^Nov 10" messages.1

13. End of the line $ using dollar symble

grep "terminating.$" messages

? The preceding item is optional and matched at most once.

* The preceding item will be matched zero or more times.

+ The preceding item will be matched one or more times.

n The preceding item is matched exactly n times.

n, The preceding item is matched n or more times.

,m The preceding item is matched at most m times.

n,m The preceding item is matched at least n times, but not more than m times.

From the above output you can come to know when all the messages has got interrupt. Just like ^ matches the beginning of the line only if it is the first character, $ matches the end of the line only if it is the last character in a regular expression.

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SELinux - Security Enhanced Linux Explained RHEL 7 - RHCSA - TechArkit

SeLinux : Security Enchanced Linux

SeLinux will support

. Port Level Security

. Sevice Level Security

. File Level Security

simply we can say 3 layer secuity.

SeLinux having 3 modes to manage security.

1. Enforcing: which means SeLinux is running with full enforcing mode, simple enabled mode.

2. Permissive: Permissive also says that SeLinux is running but it will not enforce, it will only logs the information.

3. Disabled: disable mode is simply disabled. SeLinux not in use.

Immediatly we get an question in mind that why there are three modes, Enable and disable modes are enough right.

Yes, i also got the same question when i was learning SeLinux. There is a reason behind that.

When we want to change the SeLinux mode from Enforcing to disabled we have to edit the configuration file /etc/selinux/config and change the SELINUX=disabled, config file will not be effected until unless server is rebooted.

Same for the changing the disabled mode to Enforcing mode.

but if you want to change Selinux mode from Enforcing to permissive doesn't required an reboot.

Now we understand that why SeLinux is disgned to have 3 modes.

Whenever you change the SeLinux mode from disable to enforcing after the reboot it will relabel all the SeLinux policies.

whenever you changed the SeLinux mode from Enforcing to Disabled after the reboot all the SeLinux policies will not go off, policies still exists but will not enforce.

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Syslog Server Analyzing and Storing Logs - RHCSA

OpenSSH (Secure Shell) Server and Client Configuration - RHCSA

1. A cryptographic handshake is made so that the client can verify that it is communicating with the correct server.

2. The transport layer of the connection between the client and remote host is encrypted using a symmetric cipher.

3. The client authenticates itself to the server.

4. The client interacts with the remote host over the encrypted connection.

openssh-server package installed

X11 forwarding

ssh -Y username@hostname

ssh -L local-port:remote-hostname:remote-port username@hostname

sshd(8) — The manual page for the sshd daemon documents available command line options and provides a complete list of supported configuration files and directories.

ssh(1) — The manual page for the ssh client application provides a complete list of available command line options and supported configuration files and directories.

scp(1) — The manual page for the scp utility provides a more detailed description of this utility and its usage.

sftp(1) — The manual page for the sftp utility.

ssh-keygen(1) — The manual page for the ssh-keygen utility documents in detail how to use it to generate, manage, and convert authentication keys used by ssh.

ssh_config(5) — The manual page named ssh_config documents available SSH client configuration options.

sshd_config(5) — The manual page named sshd_config provides a full description of available SSH daemon configuration options.

SSH (Secure Shell) is a protocol which facilitates secure communications between two systems using a client-server architecture and allows users to log in to server host systems remotely. Unlike other remote communication protocols, such as FTP or Telnet, SSH encrypts the login session, rendering the connection difficult for intruders to collect unencrypted passwords.

The ssh program is designed to replace older, less secure terminal applications used to log in to remote hosts, such as telnet or rsh. A related program called scp replaces older programs designed to copy files between hosts, such as rcp. Because these older applications do not encrypt passwords transmitted between the client and the server, avoid them whenever possible. Using secure methods to log in to remote systems decreases the risks for both the client system and the remote host.

Red Hat Enterprise Linux includes the general OpenSSH package, openssh, as well as the OpenSSH

server, openssh-server, and client, openssh-clients, packages. Note, the OpenSSH packages require the

OpenSSL package openssl-libs, which installs several important cryptographic libraries, enabling

OpenSSH to provide encrypted communications.

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How to Get Help From Linux Command Line and Man Pages - RHCSA

Getting Help From Command Line

:: Getting Help From Command Line ::

Not most of the production Server will have access to internet, because of security reasons, wihtout internet access how you can get an help using your command line interface. which is not a step by step guide but it will give you an idea to execute the commands and how commands works.

In Order to get the help, we have to use below commands in most of the situations.

1. Man
2. Pinfo
3. Command --help
4. Info
5. Help command

Man is the system's manual pager. Each page arugument given to man is normally the name of program, utility or function.

1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]

man ls

man -a intro

man -t alias | lpr -Pps

man -k printf

man -s 3 -K "open"

Spacebar – Scrolling man page down

PageDown/Down Arrow – Scrolling man page down

PageUp/Up Arrow – Scrolling man page UP

/string – Search for particular string

n (key) – Repeat search Up to down

N (key) – Repeat search Down to up

g – Go to first to man page

G – Go to end of the man page

q – Exit from man page

pinfo

info

Whereis

whatis

command --help

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