Basics of Redhat Enterprise Linux

The first version of Red Hat Enterprise Linux to bear the name originally came onto the market as "Red Hat Linux Advanced Server". In 2003 Red Hat rebranded Red Hat Linux Advanced Server to "Red Hat Enterprise Linux AS", and added two more variants, Red Hat Enterprise Linux ES and Red Hat Enterprise Linux WS.

Red Hat uses strict trademark rules to restrict free re-distribution of their officially supported versions of Red Hat Enterprise Linux but still freely provides its source code. Third-party derivatives can be built and redistributed by stripping away non-free components like Red Hat's trademarks. Examples include community-supported distributions like CentOS and Scientific Linux, and commercial forks like Oracle Linux.

Versions:

RHEL 8

RHEL 7

RHEL 6

RHEL 5

RHEL 4

RHEL 3

RHEL 2.1

Run levels in Redhat Enterprise Linux:::

0--> SYSTEM SHUTDOWN
1--> SINGLE USER MODE
2--> CLI MULTIUSER MODE
3--> CLI MULTIUSER MODE WITH ALL SERVICES
4--> NOT USED
5--> GUI
6--> SYSTEM RESTATE


To Check Runlevel:::
#runlevel

To Change Runlevel:::
#init 0 ---> shutdown
#init 3 ---> CLI
#init 5 ---> GUI

To open The new terminal:::
Right Click + D

Switch Between Runlevels:::
CTRL+ALT+F2 to CTRL+ALT+F6

To Clear Screen:::
#clear or CTRL+L

To Logout:::
CTRl+D


What is Shell?

Shell is a program that interepts commands and acts as nan intermidetery between user and inner working of the Operating System.

To View The Shell:::
#echo $shell 
Where, Echo= command to print, $= positional parameter, Shell=variable
[root@localhost Desktop]#
where, root=login user, localhost=hostname, Desktop=current working directory.
# -high privilage users
$  standard user - {test user}

To see the current working directory:::
#pwd , where pwd  present working directory

To Change The Directory:::
#cd

EG:: #cd /etc/passwd

To List The Directory:::
#ls /root - simple listing content of root
#ls –l /root - long listing content of root
#ls -la /root  - hideen file listing content of root
#ls -lh /root  - listing content of root in human redable form
#ls -l /root - info of root

..=current working directory
.=parent working directory

To Change The Password Of User:::
#passwd <username>

To View Customized Output::

#head -10 /etc/group {first 10 lines of file}
#head –5 /etc/group  {first 5 lines of file}
#tail /etc/group  {last 10 lines of file}
#tail –n5 /etc/group  {last 5 lines of file}

To View The Content Of File:::
#cat /etc/group

To View The Line Word And Character Of Any File::

#wc /etc/group - {to view the line word and character of file}
#wc -l /etc/group - {to view the line word of file}
#wc -c /etc/group - {to view the character of file}
#wc -w /etc/group - {to view the word of file}

To Lock The Screen::
CTRL+ALT+L

To View The History Of Commands:::
#history

When We Create A New User Four Files Were Changes:::

      1.  /etc/passwd -user information
      2.  /etc/group -group information
      3.  /etc/shadow -user password information
      4.  /etc/gshadow -group password information

Three Part Of Command :::

#ls –l /root
where,
ls -Command
-l - Option
/root- Arguments