Linux Training Notes

Started Study on June 8, 2026 ←

Section 3: System Access and Filesystems

Linux Root Directories

/ - The root directory
/boot - Boot loader files, contains grub.cfg
/dev - System device files
/bin - Everyday user commands
/sbin - System/filesystem commands
/etc - System configuration files
/home - User home directories
/lib - Essential shared libraries and kernel modules
/media - Mount points for removable media
/mnt - Temporarily mounted filesystems
/opt - Optional application software packages
/proc - Virtual filesystem providing process and system information
/root - Home directory for the root user
/run - Runtime data for running processes
/srv - Service data
/sys - Virtual filesystem providing an interface to kernel data structures
/tmp - Temporary files
/usr - User binaries, libraries, and documentation
/var - Variable data such as logs and spool files

Important Filesystem Commands

cd - Change directory
ls - List directory contents
pwd - Print working directory

File Management

touch - Create an empty file
cp - Copy files and directories
mv - Move or rename files and directories
vi - Edit files
mkdir - Create a directory
rmdir - Remove an directory
chgrp - Change group ownership
chmod - Change file permissions

Find Files and Diectories

find
locate

File Types

- - Regular file
d - Directory
l - Symbolic link
c - Special file or device file
s - Socket file
p - Named pipe (FIFO)
b - Block device file

Soft and Hard Links

inode: A number that uniquely identifies a file or directory in the filesystem
Soft link (symbolic link): A file that points to another file or directory by its path
Hard link: A directory entry that points to an inode

Section 4:

Filters / Text Procesors Commands

cut - Extract columns from a file
awk - Designed for data extraction, mostly used to extract fields from output
cat seinfeld-characters | awk '{$2="Osborne" ; print $0}'
awk 'length($0) > 15' seinfeld-characters
ls -l | awk '{if($9 == "seinfeld") print $0;}'
ls -l | awk '{print NF}'

grep - Search for keyword in files/output
grep Seinfeld seinfeld-characters
grep -c Seinfeld seinfeld-characters (count entries)
grep -n Seinfeld seinfeld-characters (show line numbers)
grep -i Seinfeld seinfeld-characters (ignore case)
grep -v Seinfeld seinfeld-characters (show those without a match)
grep -v Seinfeld seinfeld-characters | awk '{print $1}' | cut -c1-3

egrep - Search for multiple keywords
egrep -i "Seinfeld|Kramer" seinfeld-characters

sort - Sort lines of text files
uniq - Report or filter out duplicate lines
wc - Word count