The mailing list for listmasters using Sympa

[Sean Hennessee <address@concealed>]

Thanks for your help Steve.

I tried manually restarting Sympa with the stop/sleep/start commands you 
suggested, but Sympa is still writing to the old log file.

I just updated my logrotate.d/sympa file to this:
/var/log/sympa.log {
    daily
    missingok
    ifempty
    copytruncate
    dateext
    dateformat %Y%m%d.
    create 640 sympa sympa
    postrotate
        /etc/init.d/sympa stop
        sleep 30
        /etc/init.d/sympa start
    endscript
}

and manually ran logrotate:
logrotate /etc/logrotate.conf
and manually restarted Sympa again:
service sympa stop
service sympa start
but it did not change anything to do with the logs, (and gave no errors); 
sympa is still writing to the old log file.
[root]# ll /var/log/sympa.log*
-rw-r----- 1 sympa sympa    0 Oct  9 10:48 /var/log/sympa.log
-rw-r----- 1 sympa sympa  57M Jun 20 10:52 /var/log/sympa.log-20130620
-rw-r----- 1 sympa sympa 509M Aug 19 08:18 /var/log/sympa.log-20130624
-rw-r----- 1 sympa sympa  50M Oct  3 06:36 /var/log/sympa.log-20130820
-rw-r----- 1 sympa sympa  84M Oct  9 13:47 /var/log/sympa.log-20131004


This is very confusing. I have a pretty good understanding of Redhat and 
basic linux ideas, but none of this is making any sense. I even checked the 
log file, "tailf sympa.log-20131004", to make sure it was actually still 
writing to that specific file, and it was/is. I'm thinking about rebooting 
the server and seeing if that gets it to start a new log file, but that is 
not a good solution for a daily 'kick'.

Peace,
Sean
--
Sean Hennessee
Enterprise & Unix Services
Office of Information Technology
UC Irvine


On Oct 9, 2013, at 12:29 PM, Steve Shipway <address@concealed> wrote:

Using logrotate on sympa log files.

The problem here is that logrotate normally works by renaming the old file 
and creating a new one.  However, if the application (sympa, in this case) 
does a single open of a file descriptor for the logging file, then this FD 
will continue to point to the old file, until (for some reason) it does a 
reopen.  Hence, the new file has length 0 and the oldfile continues to grow.

To get around this, logrotate has a couple of options.  Firstly,  it can 
perform actions after the rotate - such as sending a SIGHUP to the relevant 
daemon, so that it knows it is time to re-open the log files.  This method is 
used for many daemons; if you have a PID file for sympa, then you can add a 
post rotate script to do a "kill -HUP `cat $pidfile`".  

Unfortunately, not all applications will catch SIGHUP and trigger a log file 
re-opening.  In particular, sympa uses SIGHUP to indicate a request to stop 
detailed logging so this is no use.

What you can do, is to have a postrotate action of "/etc/init.d/sympa 
restart".  However this can be problematic with a large list server, which 
takes longer to shut down the sympa.pl process, so you might instead like to 
do this:

       postrotate
              /etc/init.d/sympa stop
              sleep 30
              /etc/init.d/sympa start
       endscript

You can adjust the sleep time for whatever works for you.  Of course, your 
list server is inactive during the rotate, but this is unlikely to be 
problematic unless you have a seriously high throughput... (We use this 
method).

The second option you have is using copytruncate.  This makes logrotate copy 
the log file and truncate the old one, instead of renaming and creating a new 
one.  This means that the sympa process can keep its FD open to the file 
without having to restart.  However, there is a small race condition that 
means you may lose a log entry between the copy and the truncate actions; 
also, there is a chance that for some reason the append doesnt combine with 
the truncate correctly, so you should test it out first.

The best solution can only be done by the Sympa development team - have sympa 
respond to a signal (SIGUSR1?) by re-opening its log files, allowing a smooth 
transition by logrotate.

Steve

Steve Shipway
University of Auckland ITS
UNIX Systems Design Lead
address@concealed
Ph: +64 9 373 7599 ext 86487