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Collect Syslog events with Azure Monitor Agent

Syslog events is one of the data sources used in a data collection rule (DCR). Details for the creation of the DCR are provided in Collect data with Azure Monitor Agent. This article provides additional details for the Syslog events data source type.

Syslog is an event logging protocol that's common to Linux. You can use the Syslog daemon that's built into Linux devices and appliances to collect local events of the types you specify. Applications send messages that are either stored on the local machine or delivered to a Syslog collector.

Tip

To collect data from devices that don't allow local installation of Azure Monitor Agent, configure a dedicated Linux-based log forwarder.

Prerequisites

Configure collection of Syslog data

In the Collect and deliver step of the DCR, select Linux Syslog from the Data source type dropdown.

The following facilities are supported with the Syslog collector:

Pri index Pri Name
0 None
1 Kern
2 user
3 mail
4 daemon
4 auth
5 syslog
6 lpr
7 news
8 uucp
9 ftp
10 ntp
11 audit
12 alert
13 mark
14 local0
15 local1
16 local2
17 local3
18 local4
19 local5
20 local6
21 local7

Screenshot that shows the page to select the data source type and minimum log level.

By default, the agent will collect all events that are sent by the Syslog configuration. Change the Minimum log level for each facility to limit data collection. Select NONE to collect no events for a particular facility.

Destinations

Syslog data can be sent to the following locations.

Destination Table / Namespace
Log Analytics workspace Syslog

Note

Azure Monitor Linux Agent versions 1.15.2 and higher support syslog RFC formats including Cisco Meraki, Cisco ASA, Cisco FTD, Sophos XG, Juniper Networks, Corelight Zeek, CipherTrust, NXLog, McAfee, and Common Event Format (CEF).

Screenshot that shows configuration of an Azure Monitor Logs destination in a data collection rule.

Configure Syslog on the Linux agent

When Azure Monitor Agent is installed on a Linux machine, it installs a default Syslog configuration file that defines the facility and severity of the messages that are collected if Syslog is enabled in a DCR. The configuration file is different depending on the Syslog daemon that the client has installed.

Rsyslog

On many Linux distributions, the rsyslogd daemon is responsible for consuming, storing, and routing log messages sent by using the Linux Syslog API. Azure Monitor Agent uses the TCP forward output module (omfwd) in rsyslog to forward log messages.

The Azure Monitor Agent installation includes default config files located in /etc/opt/microsoft/azuremonitoragent/syslog/rsyslogconf/. When Syslog is added to a DCR, this configuration is installed under the etc/rsyslog.d system directory and rsyslog is automatically restarted for the changes to take effect.

Note

On rsyslog-based systems, Azure Monitor Linux Agent adds forwarding rules to the default ruleset defined in the rsyslog configuration. If multiple rulesets are used, inputs bound to non-default ruleset(s) are not forwarded to Azure Monitor Agent. For more information about multiple rulesets in rsyslog, see the official documentation.

Following is the default configuration which collects Syslog messages sent from the local agent for all facilities with all log levels.

$ cat /etc/rsyslog.d/10-azuremonitoragent-omfwd.conf
# Azure Monitor Agent configuration: forward logs to azuremonitoragent

template(name="AMA_RSYSLOG_TraditionalForwardFormat" type="string" string="<%PRI%>%TIMESTAMP% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg%")
# queue.workerThreads sets the maximum worker threads, it will scale back to 0 if there is no activity
# Forwarding all events through TCP port
*.* action(type="omfwd"
template="AMA_RSYSLOG_TraditionalForwardFormat"
queue.type="LinkedList"
queue.filename="omfwd-azuremonitoragent"
queue.maxFileSize="32m"
action.resumeRetryCount="-1"
action.resumeInterval="5"
action.reportSuspension="on"
action.reportSuspensionContinuation="on"
queue.size="25000"
queue.workerThreads="100"
queue.dequeueBatchSize="2048"
queue.saveonshutdown="on"
target="127.0.0.1" Port="28330" Protocol="tcp")

The following configuration is used when you use SELinux and decide to use Unix sockets.

$ cat /etc/rsyslog.d/10-azuremonitoragent.conf
# Azure Monitor Agent configuration: forward logs to azuremonitoragent
$OMUxSockSocket /run/azuremonitoragent/default_syslog.socket
template(name="AMA_RSYSLOG_TraditionalForwardFormat" type="string" string="<%PRI%>%TIMESTAMP% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg%") 
$OMUxSockDefaultTemplate AMA_RSYSLOG_TraditionalForwardFormat
# Forwarding all events through Unix Domain Socket
*.* :omuxsock: 
$ cat /etc/rsyslog.d/05-azuremonitoragent-loadomuxsock.conf
# Azure Monitor Agent configuration: load rsyslog forwarding module. 
$ModLoad omuxsock

On some legacy systems, you may see rsyslog log formatting issues when a traditional forwarding format is used to send Syslog events to Azure Monitor Agent. For these systems, Azure Monitor Agent automatically places a legacy forwarder template instead:

template(name="AMA_RSYSLOG_TraditionalForwardFormat" type="string" string="%TIMESTAMP% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg%\n")

Syslog-ng

The Azure Monitor Agent installation includes default config files located in /etc/opt/microsoft/azuremonitoragent/syslog/syslog-ngconf/azuremonitoragent-tcp.conf. When Syslog is added to a DCR, this configuration is installed under the /etc/syslog-ng/conf.d/azuremonitoragent-tcp.conf system directory and syslog-ng is automatically restarted for the changes to take effect.

The default contents are shown in the following example. This example collects Syslog messages sent from the local agent for all facilities and all severities.

$ cat /etc/syslog-ng/conf.d/azuremonitoragent-tcp.conf 
# Azure MDSD configuration: syslog forwarding config for mdsd agent
options {};

# during install time, we detect if s_src exist, if it does then we
# replace it by appropriate source name like in redhat 's_sys'
# Forwrding using tcp
destination d_azure_mdsd {
	network("127.0.0.1" 
	port(28330)
	log-fifo-size(25000));			
};

log {
	source(s_src); # will be automatically parsed from /etc/syslog-ng/syslog-ng.conf
	destination(d_azure_mdsd);
	flags(flow-control);
};

The following configuration is used when you use SELinux and decide to use Unix sockets.

$ cat /etc/syslog-ng/conf.d/azuremonitoragent.conf 
# Azure MDSD configuration: syslog forwarding config for mdsd agent options {}; 
# during install time, we detect if s_src exist, if it does then we 
# replace it by appropriate source name like in redhat 's_sys' 
# Forwrding using unix domain socket 
destination d_azure_mdsd { 
	unix-dgram("/run/azuremonitoragent/default_syslog.socket" 
	flags(no_multi_line) ); 
};
 
log {
	source(s_src); # will be automatically parsed from /etc/syslog-ng/syslog-ng.conf 
	destination(d_azure_mdsd);
}; 

Note

Azure Monitor supports collection of messages sent by rsyslog or syslog-ng, where rsyslog is the default daemon. The default Syslog daemon on version 5 of Red Hat Enterprise Linux and Oracle Linux version (sysklog) isn't supported for Syslog event collection. To collect Syslog data from this version of these distributions, the rsyslog daemon should be installed and configured to replace sysklog.

If you edit the Syslog configuration, you must restart the Syslog daemon for the changes to take effect.

Supported facilities

The following facilities are supported with the Syslog collector:

Pri index Pri Name
0 None
1 Kern
2 user
3 mail
4 daemon
4 auth
5 syslog
6 lpr
7 news
8 uucp
9 ftp
10 ntp
11 audit
12 alert
13 mark
14 local0
15 local1
16 local2
17 local3
18 local4
19 local5
20 local6
21 local7

Syslog record properties

Syslog records have a type of Syslog and have the properties shown in the following table.

Property Description
Computer Computer that the event was collected from.
Facility Defines the part of the system that generated the message.
HostIP IP address of the system sending the message.
HostName Name of the system sending the message.
SeverityLevel Severity level of the event.
SyslogMessage Text of the message.
ProcessID ID of the process that generated the message.
EventTime Date and time that the event was generated.

Sample Syslog log queries

The following table provides different examples of log queries that retrieve Syslog records.

  • All Syslogs

      Syslog
    
  • All Syslog records with severity of error

      Syslog
      | where SeverityLevel == "error"
    
  • All Syslog records with auth facility type

      Syslog
      | where facility == "auth"
    
  • Count of Syslog records by facility

      Syslog
      | summarize AggregatedValue = count() by facility
    

Troubleshooting

Go through the following steps if you aren't collecting data from the JSON log that you're expecting.

  • Verify that data is being written to Syslog.
  • See Verify operation to verify whether the agent is operational and data is being received.

Next steps

Learn more about: