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<h1 style='display: inline' id='dtail-usage-examples'>DTail usage examples</h1><br />
<br />
<span class='quote'>Published at 2023-09-25T14:57:42+03:00</span><br />
<br />
<span>Hey there. As I am pretty busy this month personally (I am now on Paternity Leave) and as I still want to post once monthly, the blog post of this month will only be some DTail usage examples. They're from the DTail documentation, but not all readers of my blog may be aware of those!</span><br />
<br />
<span>DTail is a distributed DevOps tool for tailing, grepping, catting logs and other text files on many remote machines at once which I programmed in Go.</span><br />
<br />
<a class='textlink' href='https://dtail.dev'>https://dtail.dev</a><br />
<br />
<pre>
,_---~~~~~----._
_,,_,*^____ _____``*g*\"*,
____ _____ _ _ / __/ /' ^. / \ ^@q f
| _ \_ _|_ _(_) | @f | ((@| |@)) l 0 _/
| | | || |/ _` | | | \`/ \~____ / __ \_____/ \
| |_| || | (_| | | | | _l__l_ I
|____/ |_|\__,_|_|_| } [______] I
] | | | |
] ~ ~ |
| Let's tail those logs! |
| |
</pre>
<br />
<h2 style='display: inline' id='table-of-contents'>Table of Contents</h2><br />
<br />
<ul>
<li><a href='#dtail-usage-examples'>DTail usage examples</a></li>
<li>⇢ <a href='#commands'>Commands</a></li>
<li>⇢ <a href='#following-logs'>Following logs</a></li>
<li>⇢ <a href='#aggregating-logs'>Aggregating logs</a></li>
<li>⇢ <a href='#how-to-use-dcat'>How to use <span class='inlinecode'>dcat</span></a></li>
<li>⇢ <a href='#how-to-use-dgrep'>How to use <span class='inlinecode'>dgrep</span></a></li>
<li>⇢ <a href='#how-to-use-dmap'>How to use <span class='inlinecode'>dmap</span></a></li>
<li>⇢ <a href='#how-to-use-the-dtail-serverless-mode'>How to use the DTail serverless mode</a></li>
<li>⇢ ⇢ <a href='#serverless-map-reduce-query'>Serverless map-reduce query</a></li>
<li>⇢ ⇢ <a href='#aggregating-csv-files'>Aggregating CSV files</a></li>
<li>⇢ ⇢ <a href='#other-serverless-commands'>Other serverless commands</a></li>
</ul><br />
<h2 style='display: inline' id='commands'>Commands</h2><br />
<br />
<span>DTail consists out of a server and several client binaries. In this post, I am showcasing their use!</span><br />
<br />
<ul>
<li>Use <span class='inlinecode'>dtail</span> to follow logs</li>
<li>Use <span class='inlinecode'>dtail</span> to aggregate logs while they are followed</li>
<li>Use <span class='inlinecode'>dcat</span> to display logs and other text files already written</li>
<li>Use <span class='inlinecode'>dgrep</span> to grep (search) logs and other text files already written</li>
<li>Use <span class='inlinecode'>dmap</span> to aggregate logs and other text files already written</li>
<li><span class='inlinecode'>dserver</span> is the DTail server, where all the clients can connect to</li>
</ul><br />
<h2 style='display: inline' id='following-logs'>Following logs</h2><br />
<br />
<span>The following example demonstrates how to follow logs of several servers at once. The server list is provided as a flat text file. The example filters all records containing the string <span class='inlinecode'>INFO</span>. Any other Go compatible regular expression can also be used instead of <span class='inlinecode'>INFO</span>.</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt --grep INFO --files </font><font color="#bb00ff">"/var/log/dserver/*.log"</font>
</pre>
<br />
<span>Hint: you can also provide a comma separated server list, e.g.: <span class='inlinecode'>servers server1.example.org,server2.example.org:PORT,...</span></span><br />
<br />
<a href='./dtail-usage-examples/dtail.gif'><img alt='Tail example' title='Tail example' src='./dtail-usage-examples/dtail.gif' /></a><br />
<br />
<span class='quote'>Hint: You can also use the shorthand version (omitting the <span class='inlinecode'>--files</span>)</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt --grep INFO </font><font color="#bb00ff">"/var/log/dserver/*.log"</font>
</pre>
<br />
<h2 style='display: inline' id='aggregating-logs'>Aggregating logs</h2><br />
<br />
<span>To run ad-hoc map-reduce aggregations on newly written log lines you must add a query. The following example follows all remote log lines and prints out every few seconds the result to standard output.</span><br />
<br />
<span class='quote'>Hint: To run a map-reduce query across log lines written in the past, please use the <span class='inlinecode'>dmap</span> command instead.</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files </font><font color="#bb00ff">'/var/log/dserver/*.log'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> --query </font><font color="#bb00ff">'from STATS select sum($goroutines),sum($cgocalls),</font>
<font color="#bb00ff"> last($time),max(lifetimeConnections)'</font>
</pre>
<br />
<span>Beware: For map-reduce queries to work, you have to ensure that DTail supports your log format. Check out the documentaiton of the DTail query language and the DTail log formats on the DTail homepage for more information.</span><br />
<br />
<a href='./dtail-usage-examples/dtail-map.gif'><img alt='Tail map-reduce example' title='Tail map-reduce example' src='./dtail-usage-examples/dtail-map.gif' /></a><br />
<br />
<span class='quote'>Hint: You can also use the shorthand version:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files </font><font color="#bb00ff">'/var/log/dserver/*.log'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> </font><font color="#bb00ff">'from STATS select sum($goroutines),sum($cgocalls),</font>
<font color="#bb00ff"> last($time),max(lifetimeConnections)'</font>
</pre>
<br />
<span>Here is another example:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files </font><font color="#bb00ff">'/var/log/dserver/*.log'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> --query </font><font color="#bb00ff">'from STATS select $hostname,max($goroutines),max($cgocalls),$loadavg,</font>
<font color="#bb00ff"> lifetimeConnections group by $hostname order by max($cgocalls)'</font>
</pre>
<br />
<a href='./dtail-usage-examples/dtail-map2.gif'><img alt='Tail map-reduce example 2' title='Tail map-reduce example 2' src='./dtail-usage-examples/dtail-map2.gif' /></a><br />
<br />
<span>You can also continuously append the results to a CSV file by adding <span class='inlinecode'>outfile append filename.csv</span> to the query:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files </font><font color="#bb00ff">'/var/log/dserver/*.log'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> --query </font><font color="#bb00ff">'from STATS select ... outfile append result.csv'</font>
</pre>
<br />
<h2 style='display: inline' id='how-to-use-dcat'>How to use <span class='inlinecode'>dcat</span></h2><br />
<br />
<span>The following example demonstrates how to cat files (display the full content of the files) on several servers at once.</span><br />
<br />
<span>As you can see in this example, a DTail client also creates a local log file of all received data in <span class='inlinecode'>~/log</span>. You can also use the <span class='inlinecode'>noColor</span> and <span class='inlinecode'>-plain</span> flags (this all also work with other DTail commands than <span class='inlinecode'>dcat</span>).</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dcat --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt --files /etc/hostname</font>
</pre>
<br />
<a href='./dtail-usage-examples/dcat.gif'><img alt='Cat example' title='Cat example' src='./dtail-usage-examples/dcat.gif' /></a><br />
<br />
<span class='quote'>Hint: You can also use the shorthand version:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dcat --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt /etc/hostname</font>
</pre>
<br />
<h2 style='display: inline' id='how-to-use-dgrep'>How to use <span class='inlinecode'>dgrep</span></h2><br />
<br />
<span>The following example demonstrates how to grep files (display only the lines which match a given regular expression) of multiple servers at once. In this example, we look after some entries in <span class='inlinecode'>/etc/passwd</span>. This time, we don't provide the server list via an file but rather via a comma separated list directly on the command line. We also explore the <span class='inlinecode'>-before</span>, <span class='inlinecode'>-after</span> and <span class='inlinecode'>-max</span> flags (see animation).</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dgrep --servers server1</font><font color="#F3E651">.</font><font color="#ff0000">example</font><font color="#F3E651">.</font><font color="#ff0000">org</font><font color="#F3E651">:</font><font color="#bb00ff">2223</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files /etc/passwd </font><font color="#F3E651">\</font>
<font color="#ff0000"> --regex nologin</font>
</pre>
<br />
<span>Generally, <span class='inlinecode'>dgrep</span> is also a very useful way to search historic application logs for certain content.</span><br />
<br />
<a href='./dtail-usage-examples/dgrep.gif'><img alt='Grep example' title='Grep example' src='./dtail-usage-examples/dgrep.gif' /></a><br />
<br />
<span class='quote'>Hint: <span class='inlinecode'>-regex</span> is an alias for <span class='inlinecode'>-grep</span>.</span><br />
<br />
<h2 style='display: inline' id='how-to-use-dmap'>How to use <span class='inlinecode'>dmap</span></h2><br />
<br />
<span>To run a map-reduce aggregation over logs written in the past, the <span class='inlinecode'>dmap</span> command can be used. The following example aggregates all map-reduce fields <span class='inlinecode'>dmap</span> will print interim results every few seconds. You can also write the result to an CSV file by adding <span class='inlinecode'>outfile result.csv</span> to the query.</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dmap --servers serverlist</font><font color="#F3E651">.</font><font color="#ff0000">txt </font><font color="#F3E651">\</font>
<font color="#ff0000"> --files </font><font color="#bb00ff">'/var/log/dserver/*.log'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> --query </font><font color="#bb00ff">'from STATS select $hostname,max($goroutines),max($cgocalls),$loadavg,</font>
<font color="#bb00ff"> lifetimeConnections group by $hostname order by max($cgocalls)'</font>
</pre>
<br />
<span>Remember: For that to work, you have to make sure that DTail supports your log format. You can either use the ones already defined in <span class='inlinecode'>internal/mapr/logformat</span> or add an extension to support a custom log format. The example here works out of the box though, as DTail understands its own log format already. </span><br />
<br />
<a href='./dtail-usage-examples/dmap.gif'><img alt='DMap example' title='DMap example' src='./dtail-usage-examples/dmap.gif' /></a><br />
<br />
<h2 style='display: inline' id='how-to-use-the-dtail-serverless-mode'>How to use the DTail serverless mode</h2><br />
<br />
<span>Until now, all examples so far required to have remote server(s) to connect to. That makes sense, as after all DTail is a *distributed* tool. However, there are circumstances where you don't really need to connect to a server remotely. For example, you already have a login shell open to the server an all what you want is to run some queries directly on local log files.</span><br />
<br />
<span>The serverless mode does not require any <span class='inlinecode'>dserver</span> up and running and therefore there is no networking/SSH involved. </span><br />
<br />
<span>All commands shown so far also work in a serverless mode. All what needs to be done is to omit a server list. The DTail client then starts in serverless mode.</span><br />
<br />
<h3 style='display: inline' id='serverless-map-reduce-query'>Serverless map-reduce query</h3><br />
<br />
<span>The following <span class='inlinecode'>dmap</span> example is the same as the previously shown one, but the difference is that it operates on a local log file directly:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dmap --files /var/log/dserver/dserver</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
<font color="#ff0000"> --query </font><font color="#bb00ff">'from STATS select $hostname,max($goroutines),max($cgocalls),$loadavg,</font>
<font color="#bb00ff"> lifetimeConnections group by $hostname order by max($cgocalls)'</font>
</pre>
<br />
<span>As a shorthand version the following command can be used:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dmap </font><font color="#bb00ff">'from STATS select $hostname,max($goroutines),max($cgocalls),$loadavg,</font>
<font color="#bb00ff"> lifetimeConnections group by $hostname order by max($cgocalls)'</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> /var/log/dsever/dserver</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
</pre>
<br />
<span>You can also use a file input pipe as follows:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> cat /var/log/dserver/dserver</font><font color="#F3E651">.</font><font color="#ff0000">log </font><font color="#F3E651">|</font><font color="#ff0000"> </font><font color="#F3E651">\</font>
<font color="#ff0000"> dmap </font><font color="#bb00ff">'from STATS select $hostname,max($goroutines),max($cgocalls),$loadavg,</font>
<font color="#bb00ff"> lifetimeConnections group by $hostname order by max($cgocalls)'</font>
</pre>
<br />
<h3 style='display: inline' id='aggregating-csv-files'>Aggregating CSV files</h3><br />
<br />
<span>In essence, this works exactly like aggregating logs. All files operated on must be valid CSV files and the first line of the CSV must be the header. E.g.:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> cat example</font><font color="#F3E651">.</font><font color="#ff0000">csv</font>
<font color="#ff0000">name</font><font color="#F3E651">,</font><font color="#ff0000">lastname</font><font color="#F3E651">,</font><font color="#ff0000">age</font><font color="#F3E651">,</font><font color="#ff0000">profession</font>
<font color="#ff0000">Michael</font><font color="#F3E651">,</font><font color="#ff0000">Jordan</font><font color="#F3E651">,</font><font color="#bb00ff">40</font><font color="#F3E651">,</font><font color="#ff0000">Basketball player</font>
<font color="#ff0000">Michael</font><font color="#F3E651">,</font><font color="#ff0000">Jackson</font><font color="#F3E651">,</font><font color="#bb00ff">100</font><font color="#F3E651">,</font><font color="#ff0000">Singer</font>
<font color="#ff0000">Albert</font><font color="#F3E651">,</font><font color="#ff0000">Einstein</font><font color="#F3E651">,</font><font color="#bb00ff">200</font><font color="#F3E651">,</font><font color="#ff0000">Physician</font>
<font color="#F3E651">%</font><font color="#ff0000"> dmap --query </font><font color="#bb00ff">'select lastname,name where age > 40 logformat csv outfile result.csv'</font><font color="#ff0000"> example</font><font color="#F3E651">.</font><font color="#ff0000">csv</font>
<font color="#F3E651">%</font><font color="#ff0000"> cat result</font><font color="#F3E651">.</font><font color="#ff0000">csv</font>
<font color="#ff0000">lastname</font><font color="#F3E651">,</font><font color="#ff0000">name</font>
<font color="#ff0000">Jackson</font><font color="#F3E651">,</font><font color="#ff0000">Michael</font>
<font color="#ff0000">Einstein</font><font color="#F3E651">,</font><font color="#ff0000">Albert</font>
</pre>
<br />
<span>DMap can also be used to query and aggregate CSV files from remote servers.</span><br />
<br />
<h3 style='display: inline' id='other-serverless-commands'>Other serverless commands</h3><br />
<br />
<span>The serverless mode works transparently with all other DTail commands. Here are some examples:</span><br />
<br />
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<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail /var/log/dserver/dserver</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
</pre>
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<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><font color="#F3E651">%</font><font color="#ff0000"> dtail --logLevel trace /var/log/dserver/dserver</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
</pre>
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><font color="#F3E651">%</font><font color="#ff0000"> dcat /etc/passwd</font>
</pre>
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><font color="#F3E651">%</font><font color="#ff0000"> dcat --plain /etc/passwd </font><font color="#F3E651">></font><font color="#ff0000"> /etc/test</font>
<i><font color="#ababab"># Should show no differences.</font></i>
<font color="#ff0000">diff /etc/test /etc/passwd </font>
</pre>
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><font color="#F3E651">%</font><font color="#ff0000"> dgrep --regex ERROR --files /var/log/dserver/dsever</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
</pre>
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><font color="#F3E651">%</font><font color="#ff0000"> dgrep --before </font><font color="#bb00ff">10</font><font color="#ff0000"> --after </font><font color="#bb00ff">10</font><font color="#ff0000"> --max </font><font color="#bb00ff">10</font><font color="#ff0000"> --grep ERROR /var/log/dserver/dsever</font><font color="#F3E651">.</font><font color="#ff0000">log</font>
</pre>
<br />
<span>Use <span class='inlinecode'>--help</span> for more available options. Or go to the DTail page for more information! Hope you find DTail useful!</span><br />
<br />
<span>E-Mail your comments to <span class='inlinecode'>paul@nospam.buetow.org</span> :-)</span><br />
<br />
<span>Other related posts are:</span><br />
<br />
<a class='textlink' href='./2023-09-25-dtail-usage-examples.html'>2023-09-25 DTail usage examples (You are currently reading this)</a><br />
<a class='textlink' href='./2022-10-30-installing-dtail-on-openbsd.html'>2022-10-30 Installing DTail on OpenBSD</a><br />
<a class='textlink' href='./2022-03-06-the-release-of-dtail-4.0.0.html'>2022-03-06 The release of DTail 4.0.0</a><br />
<a class='textlink' href='./2021-04-22-dtail-the-distributed-log-tail-program.html'>2021-04-22 DTail - The distributed log tail program</a><br />
<br />
<span>I hope you find the tools presented in this post useful!</span><br />
<br />
<span>Paul</span><br />
<br />
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