DevOps, Linux ,Git , GitHub

File and Directory Management🗂️

ls: List directory contents.
- ls -l: List in long format.
- ls -a: List all files including hidden files (those starting with a dot).
- ls -lh: Long format with human-readable file sizes
cd: Change the current directory.
- Change the directory to [dir]. Use cd .. to go up one level.
pwd: Print the current working directory.
mkdir : Create a new directory. mkdir new_folder
rmdir : Remove an empty directory. rmdir old_folder
rm : Remove files or directories.
- rm -r [dir]: Remove the directory and its contents recursively.
- rm -i [file]: Remove with a prompt before every removal.

File Permissions and Ownership🛡️

chmod : Change file permissions.
- Example: chmod 755 script.sh
- chmod 755 [file_name]: Set permissions to rwxr-xr-x.
- chmod u+x [file_name]: Add execute permission for the owner.
chown : Change file owner and group.
- Example: chown user:group file.txt
chgrp : Change group ownership.
- Example: chgrp groupname file.txt

File Permissions Symbols🔑

r: Read permission.
w: Write permission.
x: Execute permission.
-: No permission.

Viewing and Editing Files📖

cat : Concatenate and display file contents.
- Example: cat file.txt
less : View file contents one screen at a time.
- Example: less file.txt
nano : Simple text editor.
- Example: nano file.txt
vi or vim : Advanced text editor.
- Example: vim file.txt

Process Management⏳

ps: Display current processes.
- Example: ps aux - Display detailed information about all running processes.
top: Display and manage processes in real-time.
- Example: top
htop: Enhanced version of top (needs to be installed).
kill: Terminate a process.
- Example: kill 1234 (terminate the process with PID 1234)
killall [process_name]: Terminate all processes with the specified name.
bg: Resume a suspended job in the background.
fg: Bring a background job to the foreground.
jobs: List all background jobs.
systemctl : Manage system services.
- Example: systemctl start nginx (start nginx service), systemctl status nginx (check status of nginx service)

Networking🌐

ifconfig: Display or configure network interfaces.
- Example: ifconfig eth0
ping [host]: Check the network connection to a server.
- Example: ping google.com
netstat: Network statistics.
- Example: netstat -tuln (List all listening ports.)
wget [url]: Download files from the web.
curl [url]: Transfer data from or to a server.
ip addr: Show IP addresses and network interfaces.

Disk Usage💾

df: Display disk space usage.
- Example: df -h human-readable format.
du: Estimate file space usage.
- Example: du -sh [file/dir]: Display summary in human-readable format.

Archive and Compression📦

tar: Archive files.
- Example: tar -cvf archive.tar folder/ (create), tar -xvf archive.tar (extract)
gzip: Compress files.
- Example: gzip file.txt
gunzip: Decompress files.
- Example: gunzip file.txt.gz
zip [archive.zip] [file/dir]: Create a zip file archive.
unzip [archive.zip]: Extract zip file archive.

Access Control Lists (ACL)🔐

getfacl [file]: Get the ACL of a file.
setfacl -m u:[user]:[permissions] [file]: Set ACL for a user.
setfacl -m g:[group]:[permissions] [file]: Set ACL for a group.
setfacl -x u:[user] [file]: Remove ACL for a user.

Searching🕵🏻

grep [pattern] [file]: Search for a pattern in a file.
grep -r [pattern] [dir]: Recursively Search in a directory.
grep -i [pattern] [file]: Search Case-insensitive file name .
find [dir] -name [pattern]: Find files by name.
locate [name]: Find files by name (uses a database, needs to be updated with updatedb).

Package Management🛒

apt update: Update package lists but it does not install or upgrade any packages.
apt upgrade: Installed or upgraded packages.
apt install [package]: Install a package.
apt remove [package]: Remove a package.
apt autoremove: Remove unnecessary packages.

Service Management🛠️

systemctl start [service]: Start a service.
systemctl stop [service]: Stop a service.
systemctl restart [service]: Restart a service.
systemctl status [service]: Check the status of a service.
systemctl enable [service]: Enable a service to start on boot.
systemctl disable [service]: Disable a service from starting on boot.

User Management👨🏻‍💻

adduser [username]: Add a new user.
passwd [username]: Change the user password.
deluser [username]: Remove a user.
usermod -aG [group] [username]: Add a user to a group.
groups [username]: Display list the groups a user is in.

Shell Scripting📜

Structure:

  #!/bin/bash
  echo "Hello"

Variables Use:

  #!/bin/bash
  NAME="Ketan"
  echo "Hello, $NAME"

Conditional Statements- If & else:

  if [ condition ]; then
    # Commands
  elif [ condition ]; then
    # Commands
  else
    # Commands
  fi

Loops- For and While:

  for i in {1..5}; do
    echo "Iteration $i"
  done

  while [ condition ]; do
    # Commands
  done

Other Commands 📑

echo [text]: Display the text.
date: Display or set the system date and time.
uptime: Show how long the system has been running.
who: Show who is logged on.
history: Show command history.

Configuration🔧

git config: Set configuration values.
- Example: git config --global user.name "Your Name",
- git config --global user.email "you@example.com"

Repository Management📂

git init: Initialize a new Git repository.
git clone: Clone a repository into a new directory.
- Example: git clone https://github.com/user/repo.git

Basic Snapshotting⚙️

git add: It will move all the files to the staging.
- Example: git add file.txt
git commit: It is used to create a new commit with a specific commit message
- Example: git commit -m "Initial commit"
git status: Show the working tree status.
git log: It will display a list of commits.
git diff: Show changes between two commit IDs and working tree, etc.

Branching and Merging🎋

git branch: List, create, or delete branches.
- Example: git branch (list), git branch new-branch (create), git branch -d old-branch (delete)
git checkout: Switch branches or restore working tree files.
- Example: git checkout new-branch (switch), git checkout -b new-branch (create and switch)
git merge: Join two or more development histories together.
- Example: git merge new-branch

Remote Repositories🍃

git remote: Manage a set of tracked repositories.
- Example: git remote -v (list), git remote add origin https://github.com/user/repo.git (add remote)
git fetch: Download objects and refs from another repository.
- Example: git fetch origin
git pull: It will pull the changes from the remote repository to the local.
- Example: git pull origin main
git push: Update the remote references along with their associated objects.
- Example: git push origin main

Rewriting History⌛

git reset: Reset current HEAD to the specified state.
- Example: git reset --hard HEAD~1 (delete all commit)
- git reset --soft HEAD~1(remove from history but store in file system/staging area)
git revert: Create a new commit that undoes the changes by creating/adding new commits.
- Example: git revert HEAD
git rebase: Reapply commits on top of another base tip and it will maintain in a linear format.
- Example: git rebase main

Additional Tips👀

.gitignore: Text file used in Git repositories to specify which files and directories should be ignored and not tracked by Git.
- Example: Add node_modules/ to .gitignore to ignore all files in the node_modules directory.

Conclusion🎯

It provides quick and concise information to help manage files, processes, permissions, and version control efficiently, thereby streamlining workflows and improving the productivity of DevOps Engineers.

Day 14: Essential Linux and Git-GitHub Cheat Sheet