Try /dev/log or /dev/klog ? 
https://man.openbsd.org/syslogd.8
syslogd opens a UDP socket, as specified in /etc/services, for sending forwarded messages. By default all incoming data on this socket is discarded. If insecure mode is switched on with -u, it will also read messages from the socket. syslogd also opens and reads messages from the UNIX-domain socket /dev/log, and from the special device /dev/klog (to read kernel messages), and from sendsyslog(2) (to read messages from userland processes).


On Wed, Nov 22, 2017 at 6:49 AM, <buckingham@nym.hush.com> wrote:
Hello forum members,

Having spent a couple of weeks on this problem I thought someone might be able to help getting syslog-ng 3.9.1 to write log files on OpenBSD 6.2.

The O/S was a fresh install, then syslog-ng and lastly BIND. No other packages except syslog-ng and BIND dependencies have been installed. No binaries or libs from BIND conflict or replace any from the syslog-ng installation.

The .conf file was copied over from an older OpenBSD system, also running an older WORKING syslog-ng (3.1.1). The required changes to the .conf were made so that syslog-ng 3.9.1 with supervisor starts and remains running. By killing the syslog-ng process I was able to test that the supervisor process restarts syslog-ng. The rc.d script starts, stops and restarts syslog-ng as expected. /usr/local/sbin/syslog-ng -s returns no errors, indicating that the config file is sane.

In /var/log the only thing it writes are syslog-ng start/stop messages. In an effort to localise the problem, a stub syslog-ng.conf was created with the following contents:
@version: 3.9.1
source s_local {
        unix-dgram("/dev/log");
        };
#
destination catchall { file(/var/log/catchall); };
log { source(s_local);  destination(catchall);  };

The permissions and ownership on /var, /var/log, /var/run, and /etc are correct according to the OpenBSD /etc/mtree/special file.  Syslog-ng starts retaining root permissions (default) and creates /dev/log if it does not exist. The syslog_ng_flags I use are:
"-R /var/run/syslog_ng.persist -c /var/run/syslog_ng.ctl -p /var/run/syslog_ng.pid"
Have tried running without any flags to see if that would help, but did not help.

The output of syslog-ng -V is:
syslog-ng 3.9.1
Installer-Version: 3.9.1
Revision:
Module-Directory: /usr/local/lib/syslog-ng
Module-Path: /usr/local/lib/syslog-ng
Available-Modules: affile,afprog,afsocket,afsql,afuser,basicfuncs,cef,confgen,cryptofuncs,csvparser,curl,date,dbparser,disk-buffer,geoip-plugin,graphite,kvformat,linux-kmsg-format,pseudofile,system-source,add-contextual-data,json-plugin,syslogformat
Enable-Debug: off
Enable-GProf: off
Enable-Memtrace: off
Enable-IPv6: on
Enable-Spoof-Source: off
Enable-TCP-Wrapper: off
Enable-Linux-Caps: off

On my hunt I foud a message on NARKIVE where a user was having the same problem with syslog-ng 3.6 on OpenBSD 5.9, there was no solution. There was a reply saying: "With the changes in 5.6 using sendsyslog(2), only syslogd picks up local syslog. Search the openbsd-ports list for syslog-ng to see some comments on it.".

 After a further search I turned up nothing that would help.

Have also tried to compile syslog-ng 3.12 from source to see if that might help solve the problem, but no success on OpenBSD.

Many thanks in advance.
CB

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