syslog – UDP local to syslog-ng and send remote. Forward syslog to remote server.

After writing an article for the rsyslog daemon about forwarding local UDP logging to a remote server using TCP – UDP local to rsyslog and send remote with TCP and compression this time going to use syslog-ng daemon for those who use it as default in their Linux distribution.
As mentioned in the previous article always use a non-blocking way of writing logs using UDP locally and then transfer (forward) the logs to the centralized log server(s). The example here transfers the web server’s access logs to a remote server. The web server is an Nginx web server.
The goal is to use

  • UDP for the client program (Nginx in the case) for non-blocking log writes.
  • TCP between our local machine and the remote syslog server – to be sure not to lose messages on bad connectivity.
  • local caching for our client machine – not to lose messages if the remote syslog is temporary unreachable.

The configuration and the commands are tested on CentOS 7, CentOS 8, Gentoo and Ubuntu 18 LTS. Check out UDP remote logging here – nginx remote logging to UDP rsyslog server (CentOS 7) to see how to build the server-side part – the syslog server accepting the syslog messages and writing them into files.

STEP 1) Listen for local UDP connections

Configuration file /etc/syslog-ng/syslog-ng.conf

source udp_local {
    network(ip( port(514) transport("udp") so_rcvbuf(67108864) log_fetch_limit(1000) max-connections(1000) log-iw-size(1000000));

Keep on reading!

nginx remote logging to UDP rsyslog server (CentOS 7)

This article will present to you all the configuration needed to remotely save access logs of an Nginx web server. All the configuration from the client and server sides is included. The client and the server use CentOS 7 Linux distribution and the configuration could be used under different Linux distribution. Probably only Selinux rules are kind of specific to the CentOS 7 and the firewalld rules are specific for those who use it as a firewall replacing the iptables. Here is the summary of what to expect:

  • Client-side – nginx configuration
  • Server-side – rsyslog configuration to accept UDP connections
  • Server-side – selinux and firewall configuration

The JSON formatted logs may be sent to a Elasticsearch server, for example. Here is how to do it – send access logs in json to Elasticsearch using rsyslog

STEP 1) Client-side – the Nginx configuration.

Nginx configuration is pretty simple just a single line with the log template and the IP (and port if not default 514) of the rsyslog server. For the record, this is the official documentation In addition it worth mentioning there could be multiple access_log directives in a single section to log simultaneously on different targets (and the templates may be different or the same). So you can set the access log output of a section locally and remotely.
Nginx configuration (probably /etc/nginx/nginx.conf or whatever is the organization of your Nginx configuration files.)

server {
     access_log      /var/log/nginx/example.com_access.log main;
     access_log      syslog:server=,facility=local7,tag=nginx,severity=info main3;

The “main” and “main3” are just names of the logging templates defined earlier (you may check rsyslog remote logging – prevent local messages to appear to see an interesting Nginx logging template).
The error log also could be remotely logged:

error_log syslog:server= debug;

STEP 2) Server-side – rsyslog configuration to accept UDP connections.

Of course, if you have not installed the rsyslog it’s high time you installed it with (for CentOS 7):

yum install -y rsyslog

To enable rsyslog to listen for UDP connections your rsyslog configuration file (/etc/rsyslog.conf) must include the following:

$ModLoad imudp
$UDPServerRun 514

Most of the Linux distributions have these two lines commented so you just need to uncomment them by removing the “#” from the beginning of the lines. If the lines are missing just add them under section “MODULES” (it should be near the first lines of the rsyslog configuration file).
Change the 514 with the number you like for the UDP listening port.
Write the client’s incoming lines of information to a different location and prevent merging with the local log messages – rsyslog remote logging – prevent local messages to appear. Include as a first rule under the rules’ section starting with “RULES” of the rsyslog configuration file (/etc/rsyslog.conf):

# Remote logging
$template HostIPtemp,"/mnt/logging/%FROMHOST-IP%.log"
if ($fromhost-ip != "" ) then ?HostIPtemp
& stop

Logs only of remote hosts are going to be saved under /mnt/logging/.log.
Keep on reading!

Receive multicast packets on CentOS 7 (and other linux distros)

There are so many web pages and blogs post for multicast traffic under linux and how to enable it, but in most of them something always is missing and if you follow them probably you’ll end up with not working setup and you’ll have to search the Internet again – some do need tuning of the linux kernel variables not to drop packets, some need tuning the firewall to allow protocols.
Here we present a real working example of a server under CentOS 7, our server has two network ports:

  1. eno1 – local unicast traffic with local IP
  2. eno2 – multicast traffic

We have multicast TV streams, which we can use through our second network interface and we want to use ffmpeg to encode the video. We have “Multicast Group:port” for every stream, which is like “IP:PORT” and in our case the port is always the same 5000. Here are the steps you need to do if you want to receive these streams.

STEP 1) Set networking and make the configuration permanent.

In CentOS 7 the network of eno2, set a local IP, in fact it does not matter the exact IP, we used local network.



The important lines are highlighted. Configure the network adapter on boot and set
Second and very important add a static route for the multicast traffic for the network interface, which is supposed to have the multicast streams (in our case “eno2”). Use file:

/etc/sysconfig/network-scripts/route-eno2 dev eno2

STEP 2) Kernel variables tuning

[srv@local ~]# for i in /proc/sys/net/ipv4/conf/*/rp_filter ; do echo 0 > "$i";   done
[srv@local ~]# echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

Turn off “Reverse Path Filtering” for all interfaces (rp_filter) and ping for the multicast address to work properly we need to disable icmp_echo_ignore_broadcasts. By default kernel drops these packets so you need this tuning or your application will not receive a single udp packet.
You could save the above two lines in


and do not forget to set proper access rights:

[srv@local ~]# chmod 755 /etc/rc.local

Or you can use


Add the following lines in it:


STEP 3) Allow UDP traffic (and/or IGMP) if you have firewall

Here the port is the “Multicast Group:port” of the IP your application will join (look the example below)

  1. firewalld – the default with CentOS 7:
    [srv@local ~]# firewall-cmd --new-zone=multicast --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-interface=eno2 --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-protocol=igmp --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-protocol=icmp --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-source= --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-source= --permanent
    [srv@local ~]# firewall-cmd --zone=multicast --add-port=5000/udp --permanent
    [srv@local ~]# firewall-cmd --reload

    We make a new zone for the multicast streams and add our interface, the sources and the port we use. We added IGMP, because in some use cases it is needed (in our it could work without IGMP added)

  2. iptables – if you have disabled firewall and still you wanted to have a firewall:
    # allow multicast addresses
    [srv@local ~]# iptables -A INPUT -p udp -d 5000 -j ACCEPT
    [srv@local ~]# iptables -A INPUT -s -j ACCEPT
    [srv@local ~]# iptables -A INPUT -p igmp -d -j ACCEPT
    [srv@local ~]# iptables -A INPUT -p icmp --icmp-type 0 -j ACCEPT

    Probably it is a good idea to see if you have current rules (with “iptables -L -v -n” or even “iptables-save”) and to see if you should use “-A” (above) or “-I” to insert the rules above the DROP rule(s).

* Example with ffmpeg joining to a multicast group

[srv@local ~]# ffmpeg -i 'udp://'
ffmpeg version 2.8.6 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.3.0 (Gentoo 5.3.0 p1.0, pie-0.6.5)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man --enable-shared --cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ --ar=x86_64-pc-linux-gnu-ar --optflags='-march=native -O2 -msse3 -fomit-frame-pointer -pipe' --disable-static --enable-avfilter --enable-avresample --disable-stripping --enable-nonfree --enable-version3 --enable-nonfree --disable-indev=alsa --disable-indev=oss --disable-outdev=alsa --disable-outdev=oss --enable-version3 --enable-bzlib --disable-runtime-cpudetect --disable-debug --disable-doc --disable-gnutls --enable-gpl --enable-hardcoded-tables --enable-iconv --disable-lzma --enable-network --enable-openssl --enable-postproc --disable-libsmbclient --enable-ffplay --enable-sdl --disable-vaapi --disable-vdpau --enable-xlib --disable-libxcb --disable-libxcb-shm --disable-libxcb-xfixes --enable-zlib --disable-libcdio --disable-libiec61883 --disable-libdc1394 --enable-libcaca --disable-openal --disable-opengl --disable-libv4l2 --disable-libpulse --enable-libopencore-amrwb --enable-libopencore-amrnb --disable-libfdk-aac --enable-libopenjpeg --disable-libbluray --disable-libcelt --disable-libgme --enable-libgsm --disable-libmodplug --disable-libopus --disable-libquvi --disable-librtmp --disable-libssh --disable-libschroedinger --disable-libspeex --enable-libvorbis --enable-libvpx --disable-libzvbi --disable-libbs2b --disable-libflite --disable-frei0r --disable-libfribidi --enable-fontconfig --disable-ladspa --disable-libass --enable-libfreetype --disable-libsoxr --enable-pthreads --enable-libvo-aacenc --disable-libvo-amrwbenc --enable-libmp3lame --disable-libaacplus --enable-libfaac --disable-libsnappy --enable-libtheora --disable-libtwolame --disable-libwavpack --disable-libwebp --enable-libx264 --disable-libx265 --enable-libxvid --enable-x11grab --disable-amd3dnow --disable-amd3dnowext --disable-fma4 --disable-xop --cpu=host
  libavutil      54. 31.100 / 54. 31.100
  libavcodec     56. 60.100 / 56. 60.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 40.101 /  5. 40.101
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
[mpeg2video @ 0xf2fa80] Invalid frame dimensions 0x0.
    Last message repeated 10 times
Input #0, mpegts, from 'udp://':
  Duration: N/A, start: 87846.990933, bitrate: 5659 kb/s
  Program 5 
      service_name    : ?TVtest
      service_provider: ?ss
    Stream #0:0[0x33]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv), 720x576 [SAR 64:45 DAR 16:9], 5467 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x34](bul): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, s16p, 192 kb/s
At least one output file must be specified

As you can see to join the multicast group and ffmpeg to start encoding you use “udp://” for input stream parameter. Here ffmpeg joins the group and receives packets successfully.

* Generic example to receive UDP multicast stream

You may use the following example in any linux distro like Ubuntu, CentOS 7, Gentoo, OpenSuse and many others to receive muticast streams

[srv@local ~]# #ifconfig or ip - use one of them
[srv@local ~]# #ifconfig
[srv@local ~]# ifconfig eno1 up
[srv@local ~]# route add -net netmask eno2
[srv@local ~]# #or ip
[srv@local ~]# ip addr add dev eno2
[srv@local ~]# ip link set eno2 up
[srv@local ~]# #allow multicast packets to the server
[srv@local ~]# for i in /proc/sys/net/ipv4/conf/*/rp_filter ; do echo 0 > "$i";   done
[srv@local ~]# echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
[srv@local ~]# #if you have firewall use the following for the iptables OR firewalld after that - use only one of them!
[srv@local ~]# iptables -A INPUT -p udp -d 5000 -j ACCEPT
[srv@local ~]# iptables -A INPUT -s -j ACCEPT
[srv@local ~]# iptables -A INPUT -p igmp -d -j ACCEPT
[srv@local ~]# iptables -A INPUT -p icmp --icmp-type 0 -j ACCEPT
[srv@local ~]# #firewalld setup
[srv@local ~]# firewall-cmd --new-zone=multicast --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-interface=eno2 --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-protocol=igmp --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-protocol=icmp --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-source= --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-source= --permanent
[srv@local ~]# firewall-cmd --zone=multicast --add-port=5000/udp --permanent
[srv@local ~]# firewall-cmd --reload