Using tee command with soft linked file

I have a script start.sh which runs another script run.sh. run.sh starts my executable.

I wanted to record what run.sh does and I used a tee command to log it into a file loglink, start.sh:

exec run.sh | tee -a loglink

loglink is a soft linked file.

I have a logic where I have 3 log files log1.txt log2.txt log3.txt, I need each file to have a max size of only 1024 bytes. So in my code I keep checking every 5 seconds if log1.txt has reached max size, if reached max size, I change the softlink loglink to point to log2.txt, same with log2.txt and log3.txt in circular way.

As per my understanding, when I change the softlink from log1.txt to log2.txt, tee should print to log2.txt, but strange, tee is still saving output to log1.txt and not log2.txt

And to add on, I see the softlink changed in ls -l I tried something ls-l | tee loglink, it does to log2.txt.

Why the tee in script start.sh is not recognising this link change? Am I missing some logic here?

Answer

In short, a filename or symbol link is just a proxy for program to tell the kernel setup the reading or writing path for the real file representation in kernel.

tee used file descriptor to represent files, as its source code(from freebsd) explains:

for (exitval = 0; *argv; ++argv)
        if ((fd = open(*argv, append ? O_WRONLY|O_CREAT|O_APPEND :
            O_WRONLY|O_CREAT|O_TRUNC, DEFFILEMODE)) < 0) {
            warn("%s", *argv);
            exitval = 1;
        } else
            add(fd, *argv);

once a file is opened, in your case, the symbol link is followed and open the target log file, after then, the path for writing do file is opened, and symbol link or filename is not need anymore.