Overview
When an EC2 instance runs low on disk space, df and du alone make it hard to pinpoint which directories are consuming the most storage. ncdu is an ncurses-based TUI tool that visually analyzes disk usage.
Installation
# Ubuntu/Debian
sudo apt-get install ncdu
# CentOS/RHEL
yum install -y ncdu
# macOS
brew install ncdu
Basic Usage
# Analyze current directory
ncdu
# Analyze a specific path
ncdu /var/log
# Analyze entire disk
ncdu /
After scanning, ncdu displays a tree of directories and files with graphical bar indicators. It’s immediately obvious where storage is being consumed.
Key Controls
| Key | Action |
|---|---|
| Arrow keys | Navigate directories |
| Enter | Enter subdirectory |
i | Item info |
d | Delete selected item (with confirmation) |
? / Shift+? | Help |
q | Quit |
How ncdu Compares to df and du
| Tool | Strengths | Weaknesses |
|---|---|---|
df | Instantly shows per-partition total usage | Doesn’t tell you which directory is the problem |
du | Calculates per-directory sizes | Output is long and sorting is tedious |
ncdu | Interactive TUI, instant sorting, in-place deletion | Requires separate installation |
Insights
For server disk management, ncdu does what htop does for process management — the same operations are possible with the basic commands (df, du), but interactive TUI navigation changes efficiency dramatically. Especially in disk-constrained environments like EC2 when disk unexpectedly fills up, ncdu handles everything from diagnosing the cause to cleaning up, all without leaving the terminal.