Rotating a nohup.out file whitout stopping the app

[igor]

I am looking for ideas on how to solve a problem with a nohup.out file
that is growing faster than expected.

While we change to a better logging mechanism we're using the stdout
to dump a bunch of debugging messages (a bunch is actually a lot!!).
Any hows, when the application runs for a few days the nohup.out file
could be 1G in size and to search for something on that file becomes a
pain in the neck.

The way I am doing that is pretty much manually. Stop the app, move
the file out and restart the app (using nohup).

I don't know if any of you guys know a better way to either rotate the
nohup.out (by date or size, don't care) or to redirect the stdout to a
logging application.

I have been looking around in the groups and on the net but can't find
anything that will give me some lights on how to do it.

Ciao,
Igor

[Jonathan Kamens]

If you use shell output redirection to send the output of an
application to a file, you can't rotate out that file and expect the
application to start writing to a new one.

You might consider looking at "logger", which will read input on stdin
and log it to the system log; then you can have logrotate or some
similar utility rotate the log periodically or when it reaches a
certain size (you can run logrotate periodically out of cron or run it
by hand when you want the file to rotate.

Another option would be to write a simple script to change it output
file whenever it has reached a certain size. Off the top of my head
(untested)....

In shell:

#!/bin/sh

# Read input until killed and redirect it to the file name specified
# on the command line with a suffix indicating the file number. No
# error checking.

FILENO=1
FILENAME=$1
SIZEMB=100

while true; do
dd bs=1MB count=$SIZEMB of=$FILENAME.$FILENO
FILENO=`expr $FILENO + 1`
done

In Perl:

#!/usr/bin/perl

$fileno = 1;
($filename = shift) || die;
$size_mb = 100;
$so_far = 0;

open(STDOUT, '>', "$filename.$fileno") || die;

$size = $size_mb * 1024 * 1024;

while (<>) {
$so_far += length;
print || die;
if ($so_far > $size) {
close(STDOUT) || die;
$fileno++;
open(STDOUT, '>', "$filename.$fileno") || die;
}
print || die;
}

close(STDOUT);

[Tim Smith]

The general thing I do with log files that I will need to rotate, if the
program or script that generates them supports writing to a pipe, is pipe
them to a program that does this:

1. Open the log file in append mode
2. Read a line on stdin
3. Lock the log file
4. Write the line
5. Unlock the log file
6. goto #2

I then have another program that basically does this:

1. Open the log file in read mode
2. Lock the log file
3. Dump the log file to stdout
4. Use ftruncate to truncate the log to 0 bytes
5. Unlock the log file