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    <p>Okay, here's an idea, inspired by <a href="http://en.wikibooks.org/wiki/Bourne_Shell_Scripting/Files_and_streams" rel="nofollow noreferrer">http://en.wikibooks.org/wiki/Bourne_Shell_Scripting/Files_and_streams</a></p> <ol> <li><p>make a named pipe:</p> <pre><code>mkfifo /dev/mypipe </code></pre></li> <li><p>redirect stdout and stderr to the named pipe:</p> <pre><code>&amp;&gt; /dev/mypipe </code></pre></li> <li><p>read from mypipe into a file:</p> <pre><code>cat &lt; /dev/mypipe &gt; /var/log/log.txt &amp; </code></pre></li> <li><p>when you need to log-rotate, kill the cat, rotate the log, and restart the cat.</p></li> </ol> <p>Now, I haven't tested this. Tell us how it goes.</p> <p>Note: you can give the named pipe any name, like /var/tmp/pipe1 , /var/log/pipe , /tmp/abracadabra , and so on. Just make sure to re-create the pipe after booting <em>before</em> your logging-script runs.</p> <hr> <p>Alternatively, don't use cat, but use a simple script file:</p> <pre><code>#!/bin/bash while : ; do read line printf "%s\n" "$line" done </code></pre> <p>This script guarantees an output for every newline read. (cat might not start outputting until its buffer is full or it encounters an EOF)</p> <hr> <h2>Final -- and TESTED -- attempt</h2> <p><strong><em>IMPORTANT NOTE:</strong> Please read the comments from <strong>@andrew</strong> below. There are several situations which you need to be aware of.</em></p> <p>Alright! Finally got access to my Linux box. Here's how:</p> <p><strong>Step 1:</strong> Make this recorder script:</p> <pre><code>#!/bin/bash LOGFILE="/path/to/log/file" SEMAPHORE="/path/to/log/file.semaphore" while : ; do read line while [[ -f $SEMAPHORE ]]; do sleep 1s done printf "%s\n" "$line" &gt;&gt; $LOGFILE done </code></pre> <p><strong>Step 2:</strong> put the recorder into work:</p> <ol> <li><p>Make a named pipe:</p> <pre><code>mkfifo $PIPENAME </code></pre></li> <li><p>Redirect your application's STDOUT &amp; STDERR to the named pipe:</p> <pre><code>...things... &amp;&gt; $PIPENAME </code></pre></li> <li><p>Start the recorder:</p> <pre><code>/path/to/recorder.sh &lt; $PIPENAME &amp; </code></pre> <p>You might want to <code>nohup</code> the above to make it survive logouts.</p></li> <li><p>Done!</p></li> </ol> <p><strong>Step 3:</strong> If you need to logrotate, pause the recorder:</p> <pre><code>touch /path/to/log/file.semaphore mv /path/to/log/file /path/to/archive/of/log/file rm /path/to/log/file.semaphore </code></pre> <p>I suggest putting the above steps into its own script. Feel free to change the 2nd line to whatever log-rotating method you want to use.</p> <hr> <p><strong><em>Note :</em></strong> If you're handy with C programming, you might want to make a short C program to perform the function of <code>recorder.sh</code>. Compiled C programs will certainly be lighter than a nohup-ed detached bash script.</p> <hr> <p><strong><em>Note 2:</em></strong> David Newcomb provided a helpful warning in the comments: <em>While the recorder is not running then writes to the pipe will block and</em> may <em>cause the program to fail unpredictably. Make sure the recorder is down (or rotating) for as short time as possible.</em></p> <p>So, if you can ensure that rotating happens <em>really</em> quickly, you can replace <code>sleep</code> (a built-in command which accepts only integer values) with <code>/bin/sleep</code> (a program that accepts float values) and set the sleep period to <code>0.5</code> or shorter.</p>
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    1. COOne thing to be careful of that I just ran into: make sure you only have one recorder.sh running, or your log file will be missing half the characters or other weirdness. This maybe sounds obvious, but I didn't think to kill it when the main process ends.
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    2. CO@andrew good point. wasn't aware of that issue, too.
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    3. COOne more thing I just fixed: when the main process is killed, the logger script reads a line from the named pipe regardless of whether there is data. This means if your process writing to the pipe fails, you'll get a ton of empty lines written to the log. I fixed this by just doing `read line; if [ "$line" != "" ]; then [do logging]; fi`
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