Filesystem Navigation
Before you can do anything useful on a Linux server, you need to know where you are, how to get somewhere else, and what the standard directory layout means. This chapter covers the essential navigation commands and gives you a map of the Linux filesystem hierarchy.
Where Am I? — pwd
pwd (Print Working Directory) tells you your current location in the filesystem.
pwd
# /home/ubuntu
Always run pwd when you first connect to a server or open a new terminal — it grounds you before you start making changes.
Listing Files — ls
ls lists the contents of a directory. On its own it shows files and directories in the current location.
# List current directory
ls
# List a specific directory
ls /etc
# List with details (permissions, owner, size, date)
ls -l
# List all files including hidden ones (starting with .)
ls -a
# Combine: long format + all files
ls -la
# Human-readable file sizes (KB, MB, GB instead of bytes)
ls -lh
# Sort by modification time, newest first
ls -lt
# Sort by modification time, oldest first (reverse)
ls -ltr
# List only directories
ls -d */
Understanding ls -la Output
drwxr-xr-x 3 ubuntu ubuntu 4096 Apr 10 09:12 .
drwxr-xr-x 10 root root 4096 Apr 9 14:33 ..
-rw-r--r-- 1 ubuntu ubuntu 220 Apr 9 14:33 .bash_logout
-rw-r--r-- 1 ubuntu ubuntu 3526 Apr 9 14:33 .bashrc
drwx------ 2 ubuntu ubuntu 4096 Apr 10 09:12 .ssh
-rw-r--r-- 1 ubuntu ubuntu 807 Apr 9 14:33 .profile
| Column | Meaning |
|---|---|
drwxr-xr-x | File type + permissions (d = directory, - = file, l = symlink) |
3 | Number of hard links |
ubuntu | Owner (user) |
ubuntu | Owner (group) |
4096 | Size in bytes |
Apr 10 09:12 | Last modification time |
.ssh | Name |
Permissions are covered in detail in Chapter 5.
Changing Directory — cd
# Go to a specific directory
cd /var/log
# Go to your home directory (three equivalent ways)
cd
cd ~
cd $HOME
# Go up one level (parent directory)
cd ..
# Go up two levels
cd ../..
# Go to the previous directory (useful for toggling between two locations)
cd -
# Go into a directory relative to where you are
cd config
cd ../other-project
Tab Completion
Press Tab to auto-complete directory and file names. If there are multiple matches, press Tab twice to see all options. This is one of the most important productivity habits to build.
cd /var/lo<Tab> # completes to /var/log/
cd /var/log/ap<Tab> # completes to /var/log/apache2/ (if it exists)
Absolute vs Relative Paths
This is one of the most important concepts to internalise.
Absolute path — starts with /. It describes the full path from the root of the filesystem. It works regardless of your current directory.
cd /home/ubuntu/projects
ls /etc/nginx/nginx.conf
cat /var/log/syslog
Relative path — does not start with /. It is interpreted relative to your current working directory.
# If you are in /home/ubuntu:
cd projects # same as cd /home/ubuntu/projects
ls .bashrc # same as ls /home/ubuntu/.bashrc
cat ../other-user/file.txt # ../ goes up one level first
When to use which:
- In scripts, prefer absolute paths for reliability. A script using
cd logswill break if run from a different directory. - Interactively, relative paths are faster to type.
The Home Directory — ~
Every user has a home directory. For ubuntu it is /home/ubuntu. For root it is /root.
The tilde ~ is a shell shorthand that always expands to your home directory:
echo ~
# /home/ubuntu
ls ~/projects
# equivalent to: ls /home/ubuntu/projects
~otheruser/file
# another user's home directory
Visualising Directory Trees — tree
tree prints a recursive directory listing as a visual tree. It is not always installed by default.
# Install on Ubuntu/Debian
sudo apt install tree
# Show tree of current directory
tree
# Limit depth (2 levels)
tree -L 2
# Show hidden files
tree -a
# Show file sizes
tree -h
# Show only directories
tree -d
# Point at a specific path
tree /etc/nginx
Example output:
/etc/nginx
├── conf.d
│ └── default.conf
├── nginx.conf
├── sites-available
│ ├── default
│ └── myapp
└── sites-enabled
└── myapp -> ../sites-available/myapp
The Linux Filesystem Hierarchy
Unlike Windows, which has drive letters (C:\, D:\), Linux has a single unified filesystem tree rooted at /. Everything — local disks, network mounts, virtual filesystems — appears somewhere under /.
Top-Level Directories
/
├── bin → Essential command binaries (ls, cp, grep)
├── boot → Bootloader and kernel files
├── dev → Device files (disks, terminals, random)
├── etc → System-wide configuration files
├── home → Home directories for regular users
├── lib → Shared libraries for binaries in /bin and /sbin
├── media → Mount points for removable media
├── mnt → Temporary mount points
├── opt → Optional / third-party software
├── proc → Virtual filesystem: process and kernel information
├── root → Home directory for the root user
├── run → Runtime data (PIDs, sockets) — cleared on boot
├── sbin → System administration binaries
├── srv → Data for services (web, FTP)
├── sys → Virtual filesystem: hardware and kernel parameters
├── tmp → Temporary files — cleared on reboot
├── usr → User programs, libraries, documentation
└── var → Variable data: logs, databases, mail, caches
Directories You Will Work With Most
/etc — Configuration
All system-wide configuration lives here. It is entirely plain-text files and directories.
ls /etc
# Key files
/etc/hostname # The machine's hostname
/etc/hosts # Static hostname-to-IP mappings
/etc/fstab # Filesystem mount configuration
/etc/passwd # User account information
/etc/group # Group definitions
/etc/sudoers # sudo permissions
/etc/ssh/sshd_config # SSH daemon configuration
/etc/crontab # System-wide cron jobs
# Key directories
/etc/nginx/ # Nginx configuration
/etc/systemd/ # systemd service definitions
/etc/apt/ # apt package manager configuration
/etc/environment # System-wide environment variables
Never delete files from /etc unless you know exactly what you are doing. Always make a backup before editing critical configuration files:
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak
/var — Variable Data
Contains data that changes at runtime: logs, databases, package cache, mail spools.
/var/log/ # Log files — you will spend a lot of time here
/var/log/syslog # General system log (Debian/Ubuntu)
/var/log/messages # General system log (RHEL/Fedora)
/var/log/auth.log # Authentication attempts
/var/log/nginx/ # Nginx access and error logs
/var/lib/ # Application state (databases, package lists)
/var/cache/apt/ # Downloaded package files
/var/run/ # Symlink to /run
/usr — User Programs
Despite the name, /usr is not user home directories — it is where installed programs and their data live.
/usr/bin/ # Programs installed for all users (node, java, python3)
/usr/sbin/ # System administration programs
/usr/lib/ # Libraries for programs in /usr/bin
/usr/local/ # Software compiled/installed manually (not via apt)
/usr/local/bin/ # Good place to put your own scripts
/usr/share/ # Architecture-independent data (man pages, icons)
When you install a package with apt install nodejs, the binary ends up in /usr/bin/node and libraries in /usr/lib/nodejs.
/tmp — Temporary Files
Any user can write to /tmp. Files here are deleted on reboot. Use it for scratch files in scripts.
# Create a temp file safely in scripts
TMPFILE=$(mktemp)
echo "data" > "$TMPFILE"
# ... process TMPFILE ...
rm "$TMPFILE"
/proc — Process and Kernel Information
/proc is a virtual filesystem — its contents are generated on-the-fly by the kernel. Reading a file here queries the kernel directly.
# Current kernel version
cat /proc/version
# CPU information
cat /proc/cpuinfo
# Memory information
cat /proc/meminfo
# Currently mounted filesystems
cat /proc/mounts
# Information about a specific process (PID 1 is init/systemd)
ls /proc/1/
cat /proc/1/cmdline
# System uptime in seconds
cat /proc/uptime
# Open file descriptors for the current shell
ls /proc/$$/fd
/dev — Devices
Physical and virtual devices appear as files here.
/dev/sda # First SATA disk
/dev/sda1 # First partition of that disk
/dev/nvme0n1 # First NVMe disk (common on modern cloud VMs)
/dev/null # The black hole — writing to it discards data
/dev/zero # Produces infinite zeros when read
/dev/random # Cryptographically secure random bytes
/dev/tty # Current terminal
# Discard output by redirecting to /dev/null
command_with_noisy_output 2>/dev/null
# Create a file filled with zeros (useful for testing disk)
dd if=/dev/zero of=/tmp/testfile bs=1M count=100
Practical Navigation Patterns
Jumping to Frequently Used Directories
# bookmark approach using shell aliases (add to ~/.bashrc)
alias proj='cd ~/projects'
alias logs='cd /var/log'
alias nginx='cd /etc/nginx'
Finding Where a Program Is Installed
# Show the full path of a command
which node
# /usr/bin/node
which java
# /usr/local/bin/java
# Show all matching locations and man page locations
whereis java
# java: /usr/bin/java /usr/share/man/man1/java.1.gz
Checking Disk Space Before You Get Stuck
A full disk is a common server emergency. Make checking disk space a habit:
# Human-readable disk usage for all mounted filesystems
df -h
# Sample output
# Filesystem Size Used Avail Use% Mounted on
# /dev/sda1 20G 12G 7.1G 63% /
# tmpfs 2.0G 0 2.0G 0% /dev/shm
If Use% climbs above 90%, investigate with du (covered in Chapter 11).