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<a href="https://frommelmak.com/lsof-practical-usage-examples.html" rel="bookmark" title="Permalink to lsof: Practical usage examples">lsof: Practical usage examples</a>
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<p>As you probably know, <code>lsof</code> stands for List of Open Files. Yes, it’s seems a simple description for a simple Unix command but, wait! Have you ever heard that everything in Unix is a file? Yes, right? So maybe this tool is more powerful than you think.</p>
<p>Let me show you how powerful it is with a bunch of practical examples (use root):</p>
<p>Lists all open files belonging to all active processes.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof
</code></pre></div>
<p>Shows all files opened by the <code>www-data</code> user </p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -u www-data
</code></pre></div>
<p>Lists just all the PIDs of the processes opened by the <code>www-data</code> user</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -t -u www-data
</code></pre></div>
<p>Kills all the activity for a particular user</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>killall -9 <span class="sb">`</span>lsof -t -u username<span class="sb">`</span>
</code></pre></div>
<p>Lists all the files opened by the process with the <code>PID</code> 234</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -p <span class="m">234</span>
</code></pre></div>
<p>Lists processes which are using a specific file.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -t /var/log/auth.log
</code></pre></div>
<p>Lists all the log files in use.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof +D /var/log
</code></pre></div>
<p>Lists all the opened files in a <span class="caps">NFS</span> folder</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof +D -N /mnt/nfsstorage
</code></pre></div>
<p>Lists of the files opened by the processes whose command begins with the characters of “chrome”.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -c chrome
</code></pre></div>
<p>Until here we were focused on regular files. But, what if we start listing special files like network files ?</p>
<p>Lists all network connections (Yes! Because everything in Unix is a file)</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i
</code></pre></div>
<p>Lists all network connections on port 80</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i:80
</code></pre></div>
<p>Lists of all network connections on privileged ports,</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i:1-1024
</code></pre></div>
<p>Lists all IPv4 connections on the system</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i4
</code></pre></div>
<p>See localhost connections.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i <span class="m">4</span>@127.0.0.1
</code></pre></div>
<p>Shows all listening <span class="caps">TCP</span>/<span class="caps">UDP</span> ports</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -Pan -i tcp -i udp
</code></pre></div>
<p>Shows all connections on port 80 using a <span class="caps">TCP</span> socket.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i TCP:80
</code></pre></div>
<p>Shows al <span class="caps">TCP</span> sockets listening on the system.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -i -sTCP:LISTEN
</code></pre></div>
<p>Shows all listening or established connection <span class="caps">TCP</span> ipv4 sockets.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -s TCP:ESTABLISHED,LISTEN -i4TCP
</code></pre></div>
<p>Check what services are still using old removed libraries and need to be reloaded.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof -n <span class="p">|</span> grep ssl <span class="p">|</span> grep DEL
</code></pre></div>
<p>Find processes that need to be restarted after updating binaries.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>sudo lsof -d txt <span class="p">|</span> grep <span class="s1">'(deleted)'</span>
</code></pre></div>
<p>And now let’s get stared with the device files.</p>
<p>Find out what processes are using your webcam.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof /dev/video0
</code></pre></div>
<p>Find out what processes are using your sound card.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>sudo lsof +D /dev/snd
</code></pre></div>
<p>The next one is one of my favorites. Displays all deleted files that are still open, and thus still occupy disk space, but are not part of any directory.
For example if you delete a big log file while it still opened by another process.</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>lsof +L1
</code></pre></div>
<p>Now the definitive one. See how <code>lsof</code> can help you to recover a deleted file!</p>
<p>Imagie you deleted the <code>syslog</code> file accidentaly. As we said before, you can see some metadata from the deleted file using <code>lsof</code>.
Using the process (<code>PID</code>), and the file descriptor (<code>FD</code>) identifiers you can recover the file:</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>COMMAND PID USER FD TYPE DEVICE SIZE/OFF NLINK NODE NAME
insync <span class="m">2432</span> frommelmak 30u REG <span class="m">8</span>,1 <span class="m">9252</span> <span class="m">0</span> <span class="m">4326104</span> /var/tmp/etilqs_KFgJC2dGc3A3p9r <span class="o">(</span>deleted<span class="o">)</span>
soffice.b <span class="m">3377</span> frommelmak 23u REG <span class="m">8</span>,1 <span class="m">4096</span> <span class="m">0</span> <span class="m">789414</span> /home/frommelmak/.execoooAMcD6a <span class="o">(</span>deleted<span class="o">)</span>
syslog-ng <span class="m">1046</span> root 10w REG <span class="m">8</span>,1 <span class="m">278428</span> <span class="m">0</span> <span class="m">20198</span> /var/log/syslog <span class="o">(</span>deleted<span class="o">)</span>
</code></pre></div>
<p>Now you can recover the file as follows:</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>cat /proc/1046/fd/10 > /var/log/syslog
</code></pre></div>
<p>If you really want to release the space used by the syslog file without restart the <code>syslog</code> process, you can do something like this:</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code>> /var/log/syslog
</code></pre></div>
<p>Or just:</p>
<div class="highlight pygments-style-monokai rounded shadow-sm mb-3"><pre><span></span><code><span class="nb">echo</span> <span class="s2">""</span> > /var/log/syslog
</code></pre></div>
<p>Finally you can put the <code>lsof</code> command in a repeat mode using <code>-|+r</code>. The prefix <code>-</code> puts the lsof in endless mode. You need to send a control signal to exit.
With the <code>+</code> prefix, <code>lsof</code> ends when there’s no output for the given parameters.</p>
<p>This article just cover the basics about <code>lsof</code>. For a complete list of features <span class="caps">RTFM</span>!</p>
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