session-04.txt

Recap
----------

pwd, cd, clear, history
ls
cat
cp mv
cut awk
curl wget
vim
chmod
grep
head
tail
touch

command-name <options> <inputs>
-l, --list
-a, --all

User management
--------------------
we need to create multiple user accounts
we create groups/teams we add users to the group...

useradd <user-name>

useradd ramesh

/root --> landing location of root user.
sudo su -
id <user-name> --> userid, user-name

in linux, when you create user, by default a group will be created with same user-name

/etc/passwd --> will have users info
getent group will have group info

passwd <user-name>

key based authentication, pub and private key

/etc/ssh/sshd_config --> SSH configuration


groupadd devops

I want to add ramesh to devops group..

usermod -g devops ramesh -> adding ramesh to devops group as primary

linux should have only 1 primary group, can have multiple secondary groups

there will be a group called testing...

groupadd testing

usermod -aG testing ramesh

gpasswd -d ramesh testing --> deleting ramesh user from testing group..

you can't remove primary group of linux user, you can only change/modify

create user --> useradd
read user --> id or cat /etc/passwd
modify user --> usermod -g or -aG <group-name> <user-name>
delete user

when employee leaving organisation
----------------------------------
delete the user

1. remove user from group
2. delete the user

ramesh --> testing
userdel ramesh --> ramesh will be removed? what about ramesh group created by default.

1. remove all his secondary groups
2. change primary group to his own group.
3. then delete the user

if a new user have to login with his private key?
-----------------------------------------------
robert user with key based authentication

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQDK9Ox5SMXHCSSf9K8pyoRmeOsYxk5y6TA2Agqn2yI4gjURxdiKYXNA21S7K+tLA3hMtBoqldT9o4FWYgZpLVxOQ8KyLXO/6TAZZcKSI3fVNaz40vaPHl84eILnbsaTZK0Sx7SrdcIpTCrccsDdfvHTu/cqD+MEhhZh0Ea0twUR9RFah7wKYNsAo7ev/bNFQD1TMt20DB9So0oyt04nMRMT0xZ+Dgs0QDhRHu+fZF4wQRPexYrKw2XMhjst0Hwicxa9DZNnJwUAsYVnEQzVsoSV+aSmmaAmRLk0ZfHLy+1RZ7/bSn3ukznXVBon2Kkrhly+twkdisrNcr8/49icT6laXyCROwMui6zKTZeo5n0ce7J46zNAsyo7nUs9wCNdnUPmkCEtb5l6G6Kh6PFu09lPDFF8wP/L/RL7kDx6sjO1yfB0hVqlxtkCJ+QreWbwqqTAJ9y5yTb76EuApmkVIWVEjvMiJ5+uMEMVRZgy0zDKCudrYSvCh39gmihm1AsswBC0I60+DD7gPZZbxmQqUzfFNLRbuEkWE5aUZTSe/HOS6UikD5mJHeBUglzX4v5WmwpHZZv4g/mEQ85QFWDgS8fVYRZ1RSt6uhiuo7gRQpjzyv0Zt1+LRzSCCDKNqwIsbgr4/SDpnlOoErIgl4PDN/TV/yKhtFnJvZ331QoiOpc1SQ== user@AshDexter-T480


mkdir .ssh
authorized_keys

R 4
W 2 
X 1

chown <user>:<group>

chown -R rober:robert .ssh

package management
----------------------
in linux, one package may be depends on another package. olden days we have rpm

rpm we have to manually get the dependencies, install them and finally main package..

yum --> automatic dependencies management

yum install git -y

/etc/yum.repos.d --> location of package URL's

yum list installed --> installed packages
yum list all --> all packages for this linux server
available = all - installed

cat /proc/cpuinfo
cat /proc/meminfo
cat /etc/os-release --> cat /etc/*release
yum update

service management
---------------------
0-65,535 ports = 65,536

SSH 22

ssh -i <private-key> user@ip

IP address, server will check is there any service running on port 22. then it will forward request to ssh

ssh servie will check credentials, if success login

Delhi --> Mumbai

if flat no, letter will stuck at security

systemctl start nginx
systemctl status nginx
systemctl stop nginx
systemctl restart nginx
systemctl enable nginx

enable --> if a service is enabled, even after restarting the server that service automatically start...

process management, network management, linux folder structure