Navigating the Linux Filesystem

The Linux Filesystem Hierarchy: Understanding /, /home, /etc, /var, /bin, and More

The Root (/)

Linux has no concept of drives and Windows/macOS file systems
everything on the system is in a tree
top of the tree is the root
standard sudirectories of root

Name	Meaning	Details
/bin	Binaries	the essential tools needed to run the system
/boot	Boot Loader	contains the static files required to start (boot) the computer houses the Linux kernel treat as 'No Entry' zone
/dev	devices	everything is a file hard drive is a file mouse is a file webcam is a file to talk to hardware apps write data to the files
/etc	Etcetera/Configuration	the nerve center of the system contains system-wide configuration files
/home	User Directories	every user on the system is given a directory inside /home if username is "anna," the home directory is /home/anna only place where permission to write files is by default
/lib	Libraries	shared code used by programs in /bin similar to .dll files in Windows
/media and /mnt	Mount Points	where external drives appear /media - usually where the system automatically attaches USB and external hard drives when they are plugged in /mnt - traditionally used by administrators to manually attach (mount) filesystems temporarily
/opt	Optional	used for third-party software which doesn't fit the standard filesystem structure
/proc	Processes	virtual file system created in memory by the kernel contains information about running apps
/root	The Root User's Home	the home directory for the user named "root" (the Superuser) regular users cannot open this directory the administrator's private office
/run	Runtime Data	storage for information that describes the system since it was booted data is deleted when the computer is restarted
/sbin	System Binaries	similar to /bin tools meant for system administration (like repairing disks or configuring networks) regular users can usually run them but they often require sudo to work
/srv	Service Data	if running a web server or an FTP server, the data intended to be served to the public is often stored here
/sys	System	virtual filesystem similar to /proc interacting with the kernel's view of the hardware
/tmp	Temporary	any file put here is deleted when the computer reboots
/usr	User System Resources	one of the largest directories contains user-installed applications, documentation, and source code /usr/bin - most programs live here /usr/share - contains shared data such as icons and fonts
/var	Variable Data	contains files that are expected to grow and change size over time /var/log - contains system logs /var/spool - contains print and mail queues /var/www - often used for web server files

Absolute vs. Relative Paths

The Absolute Path

full and complete path starting a the /root
unambiguous
always starts with a forward slash (/)

The Relative Path

never starts with a forward slash (/)
if the folder is /home/anna with a subfolder named Documents, get to Documents folder using

cd Documents

path is relative to current position in the tree

Essential Navigation Commands: ls, cd, pwd

Where Am I (pwd)

provides current folder as an absolute path

Look Around (ls)

lists contents of current directory

Change Directory (cd)

to move down from /home/anna to Documents subfolder

cd Documents

pwd command returns

/home/anna/Documents

to move to the root

cd /

pwd command returns

Understanding Directory Structure and Organization

Linux hierarchy is defined by the FHS (Filesystem Hierarchy Standard)
standard ensures consistency
regardless of distribution the configuration files are always in /etc and the logs are always in /var/log
structure allows for

Security - separating user data from system data ensures a clumsy user cannot accidentally delete the operating system
Multi-user Support - multiple users can share an app in /user/bin personal data is separate and private
Network Storage - filesystem is a logical tree
parts can be stored on different hard drives or computers
appear as just another folder to the user

Special Directories: . (current), .. (parent), ~ (home)

The Tilde (~)

represents user's home folder
to get to home folder use command

cd ~

just entering cd does the same thing

The Dot (.)

represents the current directory
to run a script in the current folder use the command

./<script name>.sh

The Double Dot (..)

represents the current folder's parent folder

The Dash (-)

to return to the previous directory use the command

cd -

Listing Files and Directories: Options for ls (-l, -a, -h)

Seeing the Details

-l flag stands for long listing
output will be similar to

drwxr-xr-x 2 anna anna 4096 Oct 27 10:00 Documents

drwxr-xr-x - permissions
- first letter tells the type
  d is the folder/file
  l is a link
- the rest determines who can read, write or execute the file
2 - number of hard links (to be covered)
anna - user who owns the file
anna - group who owns the file
4096 - file size in bytes
Oct 27 10:00 - date and time of last file modification
Documents - name of file/folder

Seeing Hidden Files (-a)

in Linux a file is hidden simply if its name starts with a dot (.)
a home directory is full of hidden configuration files which store settings for apps
to include hidden files and folders use the command

ls -a

files like .bashrc, .profile, or folders like .config will be included in the listing
deleting hidden files can reset the user's settings

Human Readable Sizes (-h)

by default file sizes a presented as bytes
58392012 bytes is not very useful
the -h flag stands for Human Readable
converts bytes to

Kilobytes (K)
Megabytes (M)
Gigabytes (G)

using the command

ls -lh

will show the file size as 4.0K or 56M

Sorting Ouput

by default the output is sort alphabetically
to sort by Time (newest first) use -t
to reverse sort order use -r
command combination is

ls -lrt

long format (-l), reversed (-r), by time (-t)

Reading File Contents: cat, less, more, head, tail

use in a terminal

cat

to view a file
dumps content to the screen

cat /etc/hostname

works well with small files

less

allows paging through file contents

less /etc/adduser.conf

navigation - use Up/Down arrows to scroll line by line
use the spacebar to scroll down a page
use 'b' to scroll up a page
search - enter command and press Enter
```
/<word to search for>
```
press 'n' to go to the next match
exit - press 'q' and Return

head

displays the first 10 lines of a file

head /etc/adduser.conf

to display a different number of lines use the -n flag
to show the first five lines

head -n 5 /etc/adduser.conf

tail

displays the last 10 lines of a file
useful for log files where newest entry is at the end of the file

tail /etc/adduser.conf

tail -f

-f flag stands for follow
tail -f displays additional lines as they are added to the file

tail -f /var/log/auth.log

Summary

Linux uses a single tree
absolute path starts with forward slash (/)
relative path does not start with forward slash (/)
cd .. moves up to parent folder
cd ~ moves to user's home folder
ls -l lists files with details
ls -a include hidden files in list
less best tool for reading large files
tail -f follows a file in real time