IT-OS-Admin-Linux

Source

• Commands: https://ss64.com/bash/
• RHEL-Trainig: https://www.redhat.com/en/services/training/rh024-red-hat-linux-technical-overview

SSH

$ sudo dnf install openssh-client
$ sudo dnf install openssh-server
$ sudo systemctl restart sshd.service
$ sudo systemctl enable sshd.service

# Key-Typs: RSA algorithm and DSA algorithm.
$ ~/.ssh/id_rsa.pvt           # The file contains the RSA private key.
$ ~/.ssh/id_rsa.pub           # The file contains the RSA public key.
$ ~/.ssh/authorized_keys      # The file contains the keys that can be used for logging into system.
...
sudo nano /etc/ssh/ssh_config
sudo nano /etc/ssh/sshd_config
------------------------------
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile %h/.ssh/authorized_keys
PasswordAuthentication no      # Yes: Can login with Password; No: Can’t login with Password
------------------------------
/etc/init.d/ssh restart

$ ssh-keygen -t rsa -f ~/.ssh/$FILENAME_KEY -C $USERNAME     # Generate prv and pub Key
$ ssh -i $PATH_PRIVATE_KEY $USERNAME@$IP_ADDRESS             # Login server with prv-key       	
...
$ ssh-copy-id –i $PATH_PUBLIC_KEY $USERNAME@IP_ADDRESS	     # Copy Pub-Key to server
$ cat ~/.ssh/id_rsa.pub | ssh user@hostname "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
$ ssh user@hostname "echo `cat ~/.ssh/id_rsa.pub` >> ~/.ssh/authorized_keys"

chmod

• u= user, g = group, o = others, a = everyone
• 4=read, 2=write, 1=execute, 0=no promission #<<-- Combination of the Digits

$ chmod u=rwx,g=rwx,o=rwx $FILE_NAME
$ chmod 755 $FILE_NAME
$ chmod uga+rwx -R $FILE_NAME      # Give permission (rwx) for (user, group, everyone)

Setting Firewall

Service

$ sudo systemctl disable firewalld
$ sudo systemctl stop firewalld
$ sudo systemctl disable NetworkManager
$ sudo systemctl stop NetworkManager
$ sudo systemctl enable network
$ sudo systemctl start network

Zone

sudo firewall-cmd --get-zones
sudo firewall-cmd --get-active-zones
sudo firewall-cmd --get-default-zone
sudo firewall-cmd --get-services
sudo firewall-cmd --list-all
sudo firewall-cmd --list-ports

Zone-home

sudo firewall-cmd --zone=home --list-all
sudo firewall-cmd --zone=home --list-ports
sudo firewall-cmd --zone=home --list-services

Setting

sudo firewall-cmd --set-default-zone=home
sudo firewall-cmd --zone=home --change-interface=eth0
sudo firewall-cmd --zone=home --add-service=http
sudo firewall-cmd --zone=home --add-port=80/tcp --permanent

New Zone "boxblue"

sudo firewall-cmd --permanent --new-zone=boxblue
sudo firewall-cmd --permanent --zone=boxblue --add-service=ssh
sudo firewall-cmd --permanent --zone=boxblue --add-service=http
sudo firewall-cmd --permanent --zone=boxblue --add-service=https
sudo firewall-cmd --permanent --zone=boxblue --add-port=80/tcp
sudo firewall-cmd --permanent --zone=boxblue --add-port=22/tcp
sudo firewall-cmd --permanent --zone=boxblue --change-interface=wlp0s19f2u1
sudo firewall-cmd --permanent --set-default-zone=boxblue

Update

sudo firewall-cmd --reload
sudo systemctl restart network
sudo systemctl reload firewalld

Vim

Source: https://vim.rtorr.com/

Esc   Exit the current mode.
i     Enter "Insert mode" for inserting text.
v     Enter "Visual mode" for character.
V     Enter "Visual mode" for line.
:     Enter "Command mode". 
...
h     Move Left
j     Move Down
k     Move Up
l     Move Right
...
ggVG  Select hole text
...
u     Undo the last operation.
d     Delete or Cut selected item.
y     Copy line.
p     Paste storage buffer after the cursor.
...
:q    Quit Vim.
:q!   Quit Vim without saving the changes.
:w    Save the file
:wq   Save the file and quit Vim.
:w $FILE_NAME Save the file with the filename "yx".

Setting User

sudo adduser –G [GROUP-ID] [USER-ID]			# Add a new Group & User
sudo deluser [USER-ID]					# Delete User
sudo remove [USER-ID]					# Remove User
...
echo "USER-ID ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
usermod -aG sudo [USER-ID]				# Add User to Sudo-Group
sudo visudo						# Add “USER-ID ALL=(ALL:ALL) ALL”
id
...	
su [USER-ID]						# Change User in current Folder
su - [USER-ID]						# Change User in User Home-Folder
sudo bash						# Login as root
sudo -i							# Login as root
sudo -i –u [USER-ID]					# Login in account user
passwd [USER-ID]					# Change User Password
gpasswd -a user-ID group-ID				#

DNF: Package Manager (fedora)

DNF: Dandified YUM

...
rpm –i filename.rpm
...
dnf --version
dnf --enablerepo=epel
...
sudo ls /etc/yum.repos.d/
sudo dnf repolist
sudo dnf repoinfo
sudo dnf config-manager --add-repo $REPO_NAME
sudo dnf config-manager --set-enabled $REPO_NAME
sudo dnf config-manager --set-disabled $REPO_NAME
...
sudo dnf copr [enable|disable|remove|list|search] <parameters>
...
dnf list installed
dnf list available
dnf provides /bin/bash
dnf search
dnf info nano
dnf install nano
dnf update nano
dnf upgrade
dnf check-update
dnf remove nano
dnf autoremove
dnf clean all
...
dnf grouplist
dnf groupinstall 'Educational Software'
dnf groupupdate 'Educational Software'
dnf groupremove 'Educational Software'
...
dnf distro-sync
dnf reinstall nano
dnf downgrade acpid