# New Page # Introduction ## Free RHEL 8 License [https://developers.redhat.com/](https://developers.redhat.com/) ## Installing RHEL in VirtualBox 1. Create the virtual network. 2. Setup the hardware: - 2 CPU cores - 4 GB RAM - 20 GB disk 3. Enable the 2nd network adapter ("Host Adapter"). ## Access to System ```bash ssh user@machine-addr ``` ## Commands Linux is case-sensitive. Documentation is usually located here: ```bash /usr/share/doc ``` Useful commands: ```bash tty ``` Know what console is in use. ```bash hostnamectl ``` Information on the host. ```bash ip addr help man ip ``` Press `q` to exit the manual page. ```bash ip -4 addr show ip -a ``` ```bash ss -ntl ``` Show listening TCP sockets. ```bash ls /usr/share/doc/ ``` ## Vagrant ```bash mkdir -p vagrant/rhel8 cd vagrant/rhel8 vagrant init generic/rhel8 vagrant up vagrant ssh ``` Register RHEL: ```bash sudo subscription-manager register --username --password ``` Power off the VM: ```bash vagrant halt ``` # Text Files ## touch Create a file: ```bash touch file1 ``` Check the file type: ```bash file file1 ``` Write text to a file: ```bash echo "hello" > file1 ``` ## Shell Redirection ### STDOUT (Standard Output) Non-error output redirected with: - `>` overwrite - `>>` append Example: ```bash ls -l /etc/hosts /etc/hosts > log ``` ### STDERR (Standard Error) Error output redirected with: - `2>` overwrite - `2>>` append Example: ```bash ls -l /etc/hosts /etc/Hosts 2> log ``` ### STDOUT and STDERR Combined Redirect both output streams: - `&>` overwrite - `&>>` append Example: ```bash ls -l /etc/hosts /etc/Hosts &> log ``` ### HEREDOCs Multiline text files: ```bash cat > story.txt <> /etc/hosts # /etc/hosts : Permission denied ``` it fails since redirection is working at the shell level under the context of the user that started the shell ```bash sudo echo "1.0.0.1 cloudflare" >> /etc/hosts # Fails as redirection from shell echo "1.0.0.1 cloudflare" | sudo tee -a /etc/hosts # Works ``` - tee file1 (overwrite) - tee -a file1 (append) ## Text editors ### nano Simple to use ```bash sudo dnf repolist sudo dnf install vim nano bash-completion ``` ```bash nano ./story.txt ``` ### vim Powerful but need to be learned ```bash vimtutor ``` ```bash vim ./story.txt ``` #### Normal mode #### Editing mode i to append before the cursor a to append after the cursor Shift + I to append at the start of the line Shift + A to append at the end of the line Esq brings back to Normal mode #### Ex mode Save or quit Esq : x to save Esq : q! to exit without saving ## Changing directories ```bash pwd # /home/bryan - print the working directory cd /usr/share/doc # to move to the directory cd # bring to the home directory cd - # bring to the previous directory mkdir my_directory # create a directory (need to have write permission) mkdir ~/my_directory # create a directory at the specified location mkdir -p parent_directory/child_directory # allow creation of a parent directory cd ESC+. # shortcut keys to recall last argument rmdir parent_directory # fails because not empty rm -rf parent_directory # remove recusivly ``` ## Files Operation ```bash # cp copy a file (need read permission and write permission where you want to copy) cp /etc/hosts . # mv move or rename (both need write) mv hosts hosts.old # rm remove (need write in the directory where the file is) rm hosts.old ``` ### Targeting a file " \* " refers to any character and any number of those characters - " \* " would target all files - file\* would target any files starting with "file" " ? " refers to any character but only one instance - " ? " would target all files with only 1 character in their name - "file?" would target any files that has 5 character and start with "file" ```bash touch files{1..12} # Create 12 files from files1 to files12 ls files* #return files1 to files12 ls files? # return files1 to files9 rm files? # remove files1 to files9 ls files?? # return files 10 to files 12 rm -i files?? # remove files 10 to files 12, -i let verify your interaction ``` ## Reading text file ### cat List the complete file. ```bash cat /etc/hosts ``` ### head Read top 10 or any specified number of lines of a file. ```bash head -n2 /etc/passwd ``` ### tail Read bottom 10 or any specified number of lines of a file. ```bash tail -n2 /etc/passwd ``` ### less Page through a file (used in man). ```bash wc -l /etc/services # wc : word count # wc -l : line count less /etc/services ``` ### grep Search through text in a file. ```bash sudo grep Password /etc/sshd_config sudo grep ^Password /etc/sshd_config # ^ : lines startting with sudo wc -l /etc/sshd_config # return ~ 145 lines sudo grep -vE '^(#|$)' /etc/sshd_config | wc -l # -v : don't show me # E : enhanced application # '^(#|$)' : line that start with # OR $ # return ~ 16 lines ```