To configure syslog-ng on a relay host, complete the following steps:
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Install the syslog-ng application on the host. For details on installing syslog-ng on specific operating systems, see Installing syslog-ng.
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Configure the network sources that collect the log messages sent by the clients.
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Create a network destination that points to the syslog-ng server.
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Create a log statement connecting the network sources to the syslog-ng server.
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Configure the local sources that collect the log messages of the relay host.
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Create a log statement connecting the local sources to the syslog-ng server.
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Enable the keep-hostname() and disable the chain-hostnames() options. (For details on how these options work, see chain-hostnames().)
NOTE: It is recommended to use these options on your syslog-ng OSE server as well.
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Set filters and options (for example, TLS encryption) as necessary.
NOTE: By default, the syslog-ng server will treat the relayed messages as if they were created by the relay host, not the host that originally sent them to the relay. In order to use the original hostname on the syslog-ng server, use the keep-hostname(yes) option both on the syslog-ng relay and the syslog-ng server. This option can be set individually for every source if needed.
If you are relaying log messages and want to resolve IP addresses to hostnames, configure the first relay to do the name resolution.
Example: A simple configuration for relays
The following is a simple configuration file that collects local and incoming log messages and forwards them to a logserver using the IETF-syslog protocol.
@version: 3.33
@include "scl.conf"
options {
time-reap(30);
mark-freq(10);
keep-hostname(yes);
chain-hostnames(no);
};
source s_local {
system(); internal();
};
source s_network {
syslog(transport(tcp));
};
destination d_syslog_tcp {
syslog("192.168.1.5" transport("tcp") port(2010));
};
log {
source(s_local); source(s_network);
destination(d_syslog_tcp);
};
Depending on your exact needs about relaying log messages, there are many scenarios and syslog-ng OSE options that influence how the log message will look like on the logserver. Some of the most common cases are summarized in the following example:
Consider the following example: client-host > syslog-ng-relay > syslog-ng-server, where the IP address of client-host is 192.168.1.2. The client-host device sends a syslog message to syslog-ng-relay. Depending on the settings of syslog-ng-relay, the following can happen.
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By default, the keep-hostname() option is disabled, so syslog-ng-relay writes the IP address of the sender host (in this case, 192.168.1.2) to the HOST field of the syslog message, discarding any IP address or hostname that was originally in the message.
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If the keep-hostname() option is enabled on syslog-ng-relay, but name resolution is disabled (the use-dns() option is set to no), syslog-ng-relay uses the HOST field of the message as-is, which is probably 192.168.1.2.
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To resolve the 192.168.1.2 IP address to a hostname on syslog-ng-relay using a DNS server, use the keep-hostname(no) and use-dns(yes) options. If the DNS server is properly configured and reverse DNS lookup is available for the 192.168.1.2 address, syslog-ng OSE will rewrite the HOST field of the log message to client-host.
NOTE: It is also possible to resolve IP addresses locally, without relying on the DNS server. For details on local name resolution, see Resolving hostnames locally.
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The above points apply to the syslog-ng OSE server (syslog-ng-server) as well, so if syslog-ng-relay is configured properly, use the keep-hostname(yes) option on syslog-ng-server to retain the proper HOST field. Setting keep-hostname(no) on syslog-ng-server would result in syslog-ng OSE rewriting the HOST field to the address of the host that sent the message to syslog-ng-server, which is syslog-ng-relay in this case.
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If you cannot or do not want to resolve the 192.168.1.2 IP address on syslog-ng-relay, but want to store your log messages on syslog-ng-server using the IP address of the original host (that is, client-host), you can enable the spoof-source() option on syslog-ng-relay. However, spoof-source() works only under the following conditions:
This section describes how to start, stop and check the status of syslog-ng Open Source Edition (syslog-ng OSE) service on Linux.
Starting syslog-ng OSE
To start syslog-ng OSE, execute the following command as root.
Example: starting syslog-ng OSE
systemctl start syslog-ng
If the service starts successfully, no output will be displayed.
The following message indicates that syslog-ng OSE can not start (see Checking syslog-ng OSE status):
Job for syslog-ng.service failed because the control process exited with error code. See systemctl status syslog-ng.service and journalctl -xe for details.
Stopping syslog-ng OSE
To stop syslog-ng OSE
- Execute the following command as root.
Example: command for stopping syslog-ng OSE
systemctl stop syslog-ng
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Check the status of syslog-ng OSE service (see Checking syslog-ng OSE status).
Restarting syslog-ng OSE
To restart syslog-ng OSE, execute the following command as root.
Example: command for restarting syslog-ng OSE
systemctl restart syslog-ng
Reloading configuration file without restarting syslog-ng OSE
To reload the configuration file without restarting syslog-ng OSE, execute the following command as root.
Example: command for reloading the configuration file without restarting syslog-ng OSE
systemctl reload syslog-ng
Checking syslog-ng OSE status
To check the following status-related components, observe the suggestions below.
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Checking the status of syslog-ng OSE service
To check the status of syslog-ng OSE service
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Execute the following command as root.
Example: command for checking the status of syslog-ng OSE service
systemctl --no-pager status syslog-ng
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Check the Active: field, which shows the status of syslog-ng OSE service. The following statuses are possible:
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Checking the process of syslog-ng OSE
To check the process of syslog-ng OSE, execute one of the following commands.
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Example: command ps u `pidof syslog-ng`
ps u `pidof syslog-ng`
Expected output example:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
syslogng 6709 0.0 0.6 308680 13432 ? Ss 09:17 0:00 /opt/syslog-ng/libexec/syslog-ng -F --no-caps --enable-core
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Example: command ps axu | grep syslog-ng | grep -v grep
ps axu | grep syslog-ng | grep -v grep
Expected output example:
syslogng 6709 0.0 0.6 308680 13432 ? Ss 09:17 0:00 /opt/syslog-ng/libexec/syslog-ng -F --no-caps --enable-core
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Checking the internal logs of syslog-ng OSE
The internal logs of syslog-ng OSE contains informal, warning and error messages.
By default, syslog-ng OSE log messages (generated on the internal() source) are written to /var/log/messages.
Check the internal logs of syslog-ng OSE for any issue.
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Message processing
The syslog-ng OSE application collects statistics about the number of processed messages on the different sources and destinations.
NOTE: When using syslog-ng-ctl stats, consider that while the output is generally consistent, there is no explicit ordering behind the command. Consequently, One Identity does not recommend creating parsers that depend on a fix output order.
If needed, you can sort the output with an external application, for example, | sort.
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Central statistics
To check the central statistics, execute the following command to see the number of received and queued (sent) messages by syslog-ng OSE.
Example: command for checking central statistics
watch "/opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^center"
The output will be updated in every 2 seconds.
If the numbers are changing, syslog-ng OSE is processing the messages.
Example: output example
Every 2.0s: /opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^center Tue Jun 25 10:33:25 2019
center;;queued;a;processed;112
center;;received;a;processed;28
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Source statistics
To check the source statistics, execute the following command to see the number of received messages on the configured sources.
Example: command for checking central statistics
watch "/opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^source"
The output will be updated in every 2 seconds.
If the numbers are changing, syslog-ng OSE is receiving messages on the sources.
Example: output example
Every 2.0s: /opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^source Tue Jun 25 10:40:50 2019
source;s_null;;a;processed;0
source;s_net;;a;processed;0
source;s_local;;a;processed;90
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Destination statistics
To check the source statistics, execute the following command to see the number of received messages on the configured sources.
Example: command for checking destination statistics
watch "/opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^source"
The output will be updated in every 2 seconds.
If the numbers are changing, syslog-ng OSE is receiving messages on the sources.
Example: output example
Every 2.0s: /opt/syslog-ng/sbin/syslog-ng-ctl stats | grep ^destination Tue Jun 25 10:41:02 2019
destination;d_logserver2;;a;processed;90
destination;d_messages;;a;processed;180
destination;d_logserver;;a;processed;90
destination;d_null;;a;processed;0
NOTE:If you find error messages in the internal logs, messages are not processed by syslog-ng OSE or you encounter any issue, you have the following options:
The syslog-ng OSE configuration file
