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KALPESH
KALPESH

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Linux Filesystem & Essential Linux Commands

#linux #cli

Linux Directory Structure

/ - Root (base) directory 🌳

/root - Home directory for root user 👑

/home - User home directories (/home/username) 🏠

/bin - Symlink to /usr/bin (user command binaries) ⚙️

/sbin - Symlink to /usr/sbin (system admin binaries) 🛠️

/usr/bin - Actual location of user binaries (ls, cat, docker) 📦

/usr/sbin - System administration binaries (useradd, nginx) 🔧

/usr/local/bin - Manually installed binaries (not managed by package manager) 📥

/lib - Essential system libraries for /bin and /sbin 📚

/opt - Third-party/commercial software packages (self-contained) 🧩

/var - Runtime data, logs, application state (Docker, Jenkins) 📊

/etc - Configuration files (editable text configs) 📝

/tmp - Temporary files (cleared on reboot) ⏳

/proc - Virtual filesystem with process/system information 🔍

/sys - Virtual filesystem with hardware/kernel information 🖥️

/boot - Boot loader files and kernel 🚀

/dev - Device files (hardware interfaces) 🔌

/mnt - Manual mount point for filesystems 💽

/media - Auto-mount point for removable devices 📀

/run - Runtime process data (PIDs, sockets) 🏃

The PATH Variable

The PATH variable in Linux is an environment variable that specifies a list of directories where executable programs are located. When you run a command in the terminal, the system searches through these directories to find the executable file corresponding to that command.

Format of the PATH Variable

The PATH variable consists of a colon (:) separated list of directories. Here's an example:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
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Example of Setting the PATH Variable

To include a new directory, such as where you have installed Terraform, you can modify the PATH variable as follows:

export PATH=$PATH:/usr/local/terraform
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After editing the file, you can apply the changes immediately by sourcing the file:

source ~/.bashrc
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Linux Commands

Gaining Root User Access 

sudo su -
logout
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Finding path 

which
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Piping Commands 

# Use the output of the first command as input for the second
|
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Debugging Commands 

# Print command in debug mode
set -x
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Error Handling in Scripts 

# Exit the script when there is an error
set -e

# Exit the script when there is a pipe failure
set -o pipefail
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Disk and Memory Usage 

# Disk usage in human-readable format
df -h

# Memory usage
free

# Number of processing units
nproc
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Real-Time Performance Monitoring 

# Monitor performance in real-time
top

# All processes running in the background
ps -ef
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Filtering Output 

# Basic filtering command
grep

# Powerful filtering and text processing
awk
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Retrieving and Downloading Information from the Internet 

# Retrieve information from the internet
curl

# Download files from the internet
wget
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Searching for Files 

# Search for the location of a file
find / -name test.sh
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Trapping Signals in Linux 

trap
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Working with Processes 

# List all processes
ps -ef

# Print errors from remote logs
curl ... | grep ...
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String Manipulation 

# Write number of occurrences of 's' in the word 'missi'
x=missi
grep -o "s" <<<"$x" | wc -l
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Scheduling Tasks with Crontab 

# Crontab in Linux
Alarm
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Editing Files 

# Open a file in read-only mode
vim -r test.txt
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Soft Links vs. Hard Links

Soft Link

  • Acts as a shortcut reference to the original file

  • The link can be broken if the original file is deleted or moved

Hard Link

  • Acts as a copy

  • Deleting the original file does not affect the hard link

Network Troubleshooting Utilities 

Traceroute
Tracepath
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Managing Large Log Files 

Logrotate
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Filtering JSON Data 

# Filter data from JSON
jq
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Filtering YAML Data 

# Filter data from YAML
yq
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Feel free to share and spread the knowledge! 🌟😊 Enjoy Learning! 😊

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