WebsiteTemplate/cheatsheets/iftop.html
2026-01-25 11:33:37 -04:00

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<h1 class="blog-page-title">iftop Cheatsheet</h1>
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<p><a href="index.html">← Back to cheatsheets</a></p>
<p><a href="../index.html">← Home</a></p>
<hr>
<p>iftop displays bandwidth usage on an interface by host connection.</p>
<hr>
<h2>Basic Usage</h2>
<ul>
<li>sudo iftop - Start on default interface</li>
</ul>
<ul>
<li>sudo iftop -i &lt;interface&gt; - Monitor specific interface</li>
</ul>
<ul>
<li>sudo iftop -i eth0 - Monitor eth0 interface</li>
</ul>
<ul>
<li>sudo iftop -i wlan0 - Monitor wlan0 interface</li>
</ul>
<hr>
<h2>Command Line Options</h2>
<ul>
<li>-i &lt;interface&gt; - Specify interface</li>
</ul>
<ul>
<li>-n - Disable hostname lookup (show IPs)</li>
</ul>
<ul>
<li>-N - Don&#39;t convert port numbers to service names</li>
</ul>
<ul>
<li>-b - Display in bytes/sec (default is bits/sec)</li>
</ul>
<ul>
<li>-B - Display in bytes/sec (alternative)</li>
</ul>
<ul>
<li>-t - Text-only mode (no bar graph)</li>
</ul>
<ul>
<li>-L &lt;num&gt; - Print length of screen</li>
</ul>
<ul>
<li>-p - Promiscuous mode</li>
</ul>
<ul>
<li>-P - Show ports</li>
</ul>
<ul>
<li>-f &lt;filter&gt; - Apply BPF filter</li>
</ul>
<ul>
<li>-F &lt;net/mask&gt; - Show traffic flows to/from network</li>
</ul>
<hr>
<h2>Interactive Commands</h2>
<h3>Navigation</h3>
<ul>
<li>j or ↓ - Scroll down</li>
</ul>
<ul>
<li>k or ↑ - Scroll up</li>
</ul>
<ul>
<li>h or ? - Show help</li>
</ul>
<ul>
<li>q - Quit</li>
</ul>
<h3>Display Toggles</h3>
<ul>
<li>n - Toggle DNS name resolution</li>
</ul>
<ul>
<li>N - Toggle service name vs port number</li>
</ul>
<ul>
<li>p - Toggle port display</li>
</ul>
<ul>
<li>s - Toggle source host display</li>
</ul>
<ul>
<li>d - Toggle destination host display</li>
</ul>
<ul>
<li>t - Cycle display modes (2s, 10s, 40s averages)</li>
</ul>
<ul>
<li>b - Toggle bar graph mode</li>
</ul>
<h3>Sorting</h3>
<ul>
<li>&lt; - Sort by source</li>
</ul>
<ul>
<li>&gt; - Sort by destination</li>
</ul>
<ul>
<li>o - Order by current sort method</li>
</ul>
<h3>Filtering</h3>
<ul>
<li>l - Set screen filter</li>
</ul>
<ul>
<li>L - Set and lock screen filter</li>
</ul>
<ul>
<li>! - Run shell command in filter line</li>
</ul>
<ul>
<li>1-9 - Filter by protocol type</li>
</ul>
<hr>
<h2>Configuration</h2>
<h3>Config File Location</h3>
<ul>
<li>No main config file (runs interactively)</li>
</ul>
<ul>
<li>Options passed via command line or aliases</li>
</ul>
<h3>Example Aliases</h3>
<p>Add to your shell config:</p>
<pre><code># Quick interface monitoring
alias iftop-eth0=&#x27;sudo iftop -i eth0 -n -N&#x27;
alias iftop-wlan0=&#x27;sudo iftop -i wlan0 -n -N&#x27;
# Bytes per second display
alias iftop-b=&#x27;sudo iftop -b -n -N&#x27;</code></pre>
<hr>
<h2>Tips</h2>
<ul>
<li>Run with root privileges (sudo) to capture on interfaces</li>
</ul>
<ul>
<li>Use -n and -N flags for less distraction in noisy networks</li>
</ul>
<ul>
<li>Exit with q, use filters in combination with command options to reduce data</li>
</ul>
<ul>
<li>Useful for spotting sudden spikes or bandwidth hogs in real time</li>
</ul>
<ul>
<li>Turn off DNS and service name lookups (-n -N) for quicker, clearer output</li>
</ul>
<ul>
<li>Press h while running to see a key reference screen</li>
</ul>
<ul>
<li>Use filters (-f) to focus on specific traffic</li>
</ul>
<ul>
<li>Watch the averages (2s, 10s, 40s) to see both momentary and sustained usage patterns</li>
</ul>
<ul>
<li>Use -b flag to display in bytes/sec if that&#39;s more intuitive</li>
</ul>
<ul>
<li>Text-only mode (-t) useful for logging or screenshots</li>
</ul>
<hr>
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