Re: multilog prematurely rotates logs if one logdir is regular file

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Hi Martin,


Am Donnerstag, dem 11.08.2022 um 00:46 +0200 schrieb Martin Castillo:

> Hi,

>=20

> for my dnscache service I wanted multilog to create a status file.

> I tried this, but initially forgot the '=3D' before the last argument:

>=20

> #!/bin/sh

> touch /run/log/dnscache.stats;

> chown log:log /run/log/dnscache.stats;

> exec chpst -u log multilog t s10000000 /var/log/dnscache \

> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 '-*' '+*stats *' /run/lo=

g/dnscache.stats

>=20

> As a result, multilog immediately quit and was restarted every

> second.=20

> That's okay. But what I didn't expect was to have my logs in=20

> /var/log/dnscache/ to be completely replaced by empty files!

>=20

> Every time multilog was started, it rotated current (even when empty)

> and deleted the oldest file. It's quite unfortunate that such a

> 'typo'=20

> deletes your log files.

>=20

> When I tried to reproduce this, I noticed that normally when multilog

> is=20

> killed, it sets the execute bit on 'current'. But when it aborts in

> the=20

> mentioned error case, it does not. When it starts, it rotates

> 'current'=20

> if it's not executable by owner.

>=20

> Maybe it should (1) check for an empty 'current' file and not rotate

> in=20

> that case or (2) properly close (mark executable/ doing the

> equivalent=20

> of c_quit()) those files in logdirs that are not related to the

> error.=20

> Though these may not be the best fixes, as I'm not too familiar with

> the=20

> code.


that sounds unfortunate. However, I'm not the 'owner' of multilog;

which is still DJB. In any case, logging is very delicate by all

aspects and the best practice is, to verify the changes appplied and

that logging is still happening.


Logging is done using buffer on FD2. If the buffer can't be emptied,

the application is stalled. Very unfortunate; but this the way it is.=20


On the server side, I can't do much. It is the user to care about

logging. If you are on Linux, you may use Lennart Poettering's systemd

and its logging facilicates. You also can check for Laurent Bercot's s6

utilities; but I can't tell, if they include a multilog alternative.


You may also use qmail's splogger to feed the syslog facility with

dnscache's output.


Sorry.


Regards.

--eh.=20


>=20

> Martin Castillo


--=20

Dr. Erwin Hoffmann | www.fehcom.de

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