On Fri, 27 Aug 2021, Jean-Baptiste Denis wrote:
So, this is a kind of gray area unless rsyslog offers some kind of blocking
mechanism that do the close/reopen and exits
when its done. rsyslog could also handle the rotation, but I have only seen a
size criteria using outchannel
(https://www.rsyslog.com/doc/master/tutorials/log_rotation_fix_size.html).
Rsyslog does not offer any blocking mechanism to close/reopen logs (I'm not
aware of any programs that do, especially not ones that work with signals as
most do, signals do not provide any option for feedback)
I guess you could query the OS to ensure that no other program has the file
open, but that seems fragile as well (imagine to programs monitoring the same
file, rsyslog may close it but they could detect each other), possibly an
inotify mechanism to detect the close, but again, how do you make sure the close
from rsyslog is what you detect.
I could also add a sleep X after sending the HUP in the postrotate script to
achieve something similar to what you
suggest. But relying on sleep to ensure that the HUP has been fully processed
does not sound reliable (at least it is
not satisfactory to me).
the delay between the signal delivery and the close will be sub-second (unless
the system is under a huge overload), so even a 1 sec delay would be very
reliable.
David Lang
Jean-Baptiste
On 8/27/21 10:18 PM, David Lang wrote:
signals (like HUP) are sent and processed asynchronously, so it can take a
little bit of time to be handled. Your
understanding is correct.
what I normally do is not use logrotate, but do the rotation myself in a script
run from cron that does the mv of the
files, sends the hub, then sleeps fora second before starting the compression
(and then normally I mv the compressed
file to a date based directory hierarchy, when you have very high log volumes,
you may want to rotate files frequently,
I've done it as frequently as every minute, and that results is LOTS of files,
more than you want in one directory)
I don't know if this can be done in the postrotate stanza of logrotate.
David Lang
On Fri, 27 Aug 2021, Jean-Baptiste Denis via rsyslog wrote:
Date: Fri, 27 Aug 2021 16:34:51 +0200
From: Jean-Baptiste Denis via rsyslog <[email protected]>
Reply-To: [email protected], rsyslog-users <[email protected]>
To: [email protected]
Cc: Jean-Baptiste Denis <[email protected]>
Subject: [rsyslog] rsyslogd HUP and logrotate
Hello,
I've got a general question about logrotate postrotate script and rsyslogHUP
signal handling interaction.
Lets say I have this logrotate section:
/var/log/messages
{
rotate 4
daily
dateext
missingok
notifempty
compress
postrotate
/usr/bin/systemctl kill -s HUP rsyslog.service >/dev/null 2>&1 || true
endscript
}
And logrotate fires up. Something like might happen:
1. /var/log/messages is rotated to /var/log/messages-20210827
2. rsyslog is still writing to /var/log/messages-20210827
3. postrotate script runs, the kill signal command returns immediately
4. logrotate start compressing /var/log/messages-20210827
The "real" handling of SIGUP happens in rsyslogd mainloop and could happen
anywhere after 3, which means also after 4.
When the /var/log/messages activity is high (about 100 messages/sec), I often
have logrotate compression step
complaining about "file size changed while zipping".
I can workaround this using the delaycompress option, but I'd like to
understand if my understanding is correct and if
there is a better/cleaner solution ?
If I'm correct until this point, I can only see two options:
- using delaycompress in logrotate block
- having a command line tool that tells rsyslogd to close and reopen the log
files AND that does not exit before
its done and use this command in postrotate
What are your thoughts ? Any suggestions ?
Thank you.
Jean-Baptiste
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