Re: [log4perl-devel] multiple process, permissions and missing log output

[Martin E. <mar...@ea...>]

Thank you to all who replied to my post. Apologies if winding my 
responses into a single email offends anyone, I am only attempting to 
save some bandwidth and the moderator some time. A few comments:

I think Log::Dispatch::FileRotate is unusable in a multi-process 
environment if the processes run as different uids. The reason is that 
you need to specify the permissions so that all uids can write to the 
file but when Log::Dispatch::FileRotate starts it attempts to do a chmod 
even if the permissions are already correct. This breaks since the file 
belongs to uid1 so the second process in as uid2 cannot do that.

Kevin Goess' suggestions:

 > a) after Log4perl::init(), loop through the directory and fix up the
 > permissions to what they should be
 >
 > b) something like this should work:
 >
 > #change effective uid while we open the log files
 > { local $> = getpwnam('nobody');  #or whoever owns them
 >    Log::Log4perl::init()
 >}

(a) works only if you remove the "permission" setting from FileRotate 
but of course falls down later when the files are automatically rotated 
because they are created afresh and now as you have not got "permission" 
set umask comes in to it. As I don't know when the files are rotated I 
cannot reapply the permission fixup, and I don't want to set umask 
process wide.

(b) similar issue to (a) when the files are rotated but not practical in 
my circumstances as the process cannot change effective uid. However, I 
guess this will work fine for John ORourke as he has Apache starting as 
root, loading his module at startup then writing to it as a "single" 
different user.

Mike Schilli said:

 > That's a feature that I think needs to be added to
 > Log::Dispatch::FileRotate, similar to what
 > Log::Log4perl::Appender::File does. FileRotate's author has been known
 > to read this mailing list, so maybe it'll come soon  :) .

A long with, don't attempt to change the permissions if they are already OK.

 > That being said, there's situations where processes are running as
 > different users, and all of them are writing to the same logfile. To
 > avoid permission problems in this scenario (think about what happens
 > when one user triggers the rotation), I've found it easiest to use an
 > external rotator instead. Log::Logperl supports this as well:
 >
 >    http://log4perl.sourceforge.net/d/Log/Log4perl/FAQ.html#2d0d0

Thanks, I read that and have tried it - it works. I was just not that 
happy about

a) sending/capturing a signal since I cannot be 100% sure what other 
modules and signals are being used. In particular one of the processes 
uses DBD::Oracle which uses the Oracle instant client and hence Net8 and 
OCI libs and these catch all sorts of signals.

b) I cannot afford to lose a single msg but also cannot afford to set 
recreate_check_interval = 0.

For the moment I've gone back to Log4perl's File Appender and set the 
"umask" setting. This at least allows me to have a single entry in the 
log4perl config file for my module and let multiple processes use my 
module. For now I've given up on automatic file rotation and I guess 
I'll have to run multiple log4perl configs and have the app stop 
log4perl logging, rename the file and start log4perl again :-(

Thanks again to all who replied.

Martin
-- 
Martin J. Evans
Easysoft Limited
http://www.easysoft.com

Martin Evans wrote:
> Hi,
> 
> I've been using Log::Log4perl for ages now in a set of CPAN modules we 
> wrote and internally in a project here. All has been ok, it works well - 
> thank you.
> 
> This issue is mostly related to Log::Dispatch::FileRotate|File but I am 
> posting here since I may need advice on an alternative.
> 
> Our log files are getting pretty large and after seeing a post on this 
> list I decided to try Log::Dispatch::FileRotate. It seemed to work fine 
> at first. The logging is in a single module, this module is used in 
> multiple places/processes under different uids and we have a single 
> config file. One of the places is code running under modperl, the other 
> is a daemon in perl.
> 
> The first problem was due to umasks and first to start (the daemon or 
> modperl) created the file and the other couldn't open it. I tried
> 
> log4perl.appender.X1.umask = sub { 0000 }
> 
> but it would seem Log::Dispatch::FileRotate does not know umask. I then 
> discovered "permissions" so did:
> 
> log4perl.appender.X1.permissions = sub { 0666 }
> 
> and this appears to work until another uid comes along in which case you 
> get:
> 
> Cannot chmod /tmp/dbix.log to 438: Operation not permitted at 
> /usr/lib/perl5/site_perl/5.8.8/Log/Dispatch/File.pm line 96
> 
> I don't get this as Log::Dispatch::File says:
> 
> "If the file does not already exist, the permissions that it should be 
> created with."
> 
> so I presume this is a bug.
> 
> Am I wasting my time here? Would I be better going back to 
> Log::Log4perl::Appender::File, using ".umask" and some external file 
> rotator? Any recommendations?
> 
> Martin