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syslog-ng Premium Edition 7.0.19 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng PE quick-start guide The syslog-ng PE configuration file Collecting log messages — sources and source drivers
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs network: Collecting messages using the RFC3164 protocol (network() driver) office365: Fetching logs from Office 365 osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps syslog: Collecting messages using the IETF syslog protocol (syslog() driver) system: Collecting the system-specific log messages of a platform systemd-journal: Collecting messages from the systemd-journal system log storage systemd-syslog: Collecting systemd messages using a socket tcp, tcp6, udp, udp6: Collecting messages from remote hosts using the BSD syslog protocol udp-balancer: Receiving UDP messages at very high rate unix-stream, unix-dgram: Collecting messages from UNIX domain sockets windowsevent: Collecting Windows event logs
Sending and storing log messages — destinations and destination drivers
elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Event Collector file: Storing messages in plain-text files hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka: Publishing messages to Apache Kafka logstore: Storing messages in encrypted files mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) pipe: Sending messages to named pipes program: Sending messages to external applications python: writing custom Python destinations sentinel: Sending logs to the Microsoft Azure Sentinel cloud smtp: Generating SMTP messages (email) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql: Storing messages in an SQL database stackdriver: Sending logs to the Google Stackdriver cloud syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng(): Forward logs to another syslog-ng node tcp, tcp6, udp, udp6: Sending messages to a remote log server using the legacy BSD-syslog protocol (tcp(), udp() drivers) unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal — usertty() destination Client-side failover
Routing messages: log paths, flags, and filters Global options of syslog-ng PE TLS-encrypted message transfer Advanced Log Transfer Protocol Reliability and minimizing the loss of log messages Manipulating messages parser: Parse and segment structured messages Processing message content with a pattern database Correlating log messages Enriching log messages with external data Monitoring statistics and metrics of syslog-ng Multithreading and scaling in syslog-ng PE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Glossary

Log types

On the Microsoft Azure Sentinel user interface, you can filter log events by referring to log-type parameters. Although the log-type parameters query information with their custom query language (namely, Kusto), they are essentially table fields in a database.

For more information about log-type parameters, see Microsoft Azure: Write data to Log Analytics repository.

For more information about the Kusto query language, see Microsoft Azure: Query Language: Overview.

The log-type parameter is mandatory for the Microsoft Azure Sentinel HTTP Data Collector API interface, and for syslog-ng Premium Edition (syslog-ng PE), its default value is Syslog_CL.

NOTE: While Microsoft Azure Sentinel accepts log events from external sources, it also has built-in log types. To differentiate external and built-in log types, Azure Sentinel automatically applies the Custom Log-type (_CL) suffix to log events that originate from external sources. Although the log-type parameter is optional (unlike workspace-id and auth-secret, which are mandatory), keep in mind that Microsoft Azure Sentinel will automatically attach the _CL suffix to all log events originating from external sources. For example, log events that originate from syslog-ng PE will be named Syslog_CL by default.

NOTE: If you want to store messages in different log types that all connect to the same workspace-id, you can create multiple sentinel() destinations that have a common workspace-id, but different log-type parameters.

Example syslog-ng PE message

When forwarding messages to Microsoft Azure Sentinel, syslog-ng PE automatically populates the following fields:

{
    "SyslogMessage": "<34>Oct 11 22:14:15 sentineluser prog1: message_begin 2020-02-10 08:29:02:329951-default message_end\n",
    "SeverityLevel": "notice",
    "ProcessID": "",
    "HostName": "myhost",
    "HostIP": "127.0.0.1",
    "Facility": "user",
    "EventTime": "2020-02-10T09:29:48+01:00",
    "Computer": "ubuntu"
}

sentinel() destination options

The sentinel() destination of syslog-ng Premium Edition (syslog-ng PE) can directly post log messages to Microsoft Azure Sentinel using its HTTP Data Collector API. The sentinel() destination has the following options.

auth-secret()
Type: Provided by Microsoft: Base64-encoded secret, identifying your application. On the syslog-ng PE side, it is handled as string.
Default: N/A

Description: A unique option for syslog-ng PE's sentinel() destination. This parameter is required so that syslog-ng PE can authenticate to Microsoft servers. You can collect the required credentials on your Microsoft Azure Sentinel Workspace.

For more information, see Getting the required credentials to configure syslog-ng PE as a Data Connector for Microsoft Azure Sentinel.

batch-bytes()
Accepted values: number [bytes]
Default: none

Description: Sets the maximum size of payload in a batch. If the size of the messages reaches this value, syslog-ng PE sends the batch to the destination even if the number of messages is less than the value of the batch-lines() option.

Note that if the batch-timeout() option is enabled and the queue becomes empty, syslog-ng PE flushes the messages only if batch-timeout() expires, or the batch reaches the limit set in batch-bytes().

Available in syslog-ng PE version 7.0.12 and later.

batch-lines()
Type: number [lines]
Default: 1

Description: Specifies how many lines are flushed to a destination in one batch. The syslog-ng PE application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency.

For example, if you set batch-lines() to 100, syslog-ng PE waits for 100 messages.

If the batch-timeout() option is disabled, the syslog-ng PE application flushes the messages if it has sent batch-lines() number of messages, or the queue became empty. If you stop or reload syslog-ng PE or in case of network sources, the connection with the client is closed, syslog-ng PE automatically sends the unsent messages to the destination.

If the batch-timeout() option is enabled and the queue becomes empty, syslog-ng PE flushes the messages only if batch-timeout() expires, or the batch reaches the limit set in batch-lines().

For optimal performance, make sure that the syslog-ng PE source that feeds messages to this destination is configured properly: the value of the log-iw-size() option of the source must be higher than the batch-lines()*workers() of the destination. Otherwise, the size of the batches cannot reach the batch-lines() limit.

batch-timeout()
Type: time [milliseconds]
Default: -1 (disabled)

Description: Specifies the time syslog-ng PE waits for lines to accumulate in the output buffer. The syslog-ng PE application sends batches to the destinations evenly. The timer starts when the first message arrives to the buffer, so if only few messages arrive, syslog-ng PE sends messages to the destination once every batch-timeout() milliseconds at most.

body()
Type: string or template
Default:

Description: The body of the HTTP request, for example, body("${ISODATE} ${MESSAGE}"). You can use strings, macros, and template functions in the body. If not set, it will contain the message received from the source by default.

body-prefix()
Accepted values: string
Default: none

Description: The string syslog-ng PE puts at the beginning of the body of the HTTP request, before the log message. Available in syslog-ng PE version 7.0.11 and later.

body-suffix()
Accepted values: string
Default: none

Description: The string syslog-ng PE puts to the end of the body of the HTTP request, after the log message. Available in syslog-ng PE version 7.0.11 and later.

ca-dir()
Accepted values: directory name
Default: none

Description: Name of a directory, that contains a set of trusted CA certificates in PEM format. The CA certificate files have to be named after the 32-bit hash of the subject's name. This naming can be created using the c_rehash utility in OpenSSL. For an example, see Configuring TLS on the syslog-ng clients. The syslog-ng PE application uses the CA certificates in this directory to validate the certificate of the peer.

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
ca-file()
Accepted values: Filename
Default: none

Description: Name of a file that contains an X.509 CA certificate (or a certificate chain) in PEM format. The syslog-ng PE application uses this certificate to validate the certificate of the HTTPS server. If the file contains a certificate chain, the file must begin with the certificate of the host, followed by the CA certificate that signed the certificate of the host, and any other signing CAs in order.

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
cert-file()
Accepted values: Filename
Default: none

Description: Name of a file, that contains an X.509 certificate (or a certificate chain) in PEM format, suitable as a TLS certificate, matching the private key set in the key-file() option. The syslog-ng PE application uses this certificate to authenticate the syslog-ng PE client on the destination server. If the file contains a certificate chain, the file must begin with the certificate of the host, followed by the CA certificate that signed the certificate of the host, and any other signing CAs in order.

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
cipher-suite()
Accepted values: Name of a cipher, or a colon-separated list
Default: Depends on the OpenSSL version that syslog-ng PE uses

Description: Specifies the cipher, hash, and key-exchange algorithms used for the encryption, for example, ECDHE-ECDSA-AES256-SHA384. The list of available algorithms depends on the version of OpenSSL used to compile syslog-ng PE. To specify multiple ciphers, separate the cipher names with a colon, and enclose the list between double-quotes, for example:

cipher-suite("ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384")

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
delimiter()
Accepted values: string
Default: newline character

Description: By default, syslog-ng PE separates the log messages of the batch with a newline character. You can specify a different delimiter by using the delimiter() option. Available in syslog-ng PE version 7.0.11 and later.

disk-buffer()

Description: This option enables putting outgoing messages into the disk-buffer file of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:

reliable()
Type: yes|no
Default: no

Description: If set to yes, syslog-ng PE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng PE crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no, the normal disk-buffer option will be used. This provides a faster, but less reliable disk-buffer option.

Caution:

Hazard of data loss! If you change the value of reliable() option when there are messages in the disk-buffer file, the messages stored in the disk-buffer file will be lost.

dir()
Type: string
Default: N/A

Description: Defines the folder where the disk-buffer files are stored.

Note that changing the value the dir() option will not move or copy existing files from the old directory to the new one.

Caution:

When creating a new dir() option for a disk-buffer file, or modifying an existing one, make sure you delete the persist file.

syslog-ng PE creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir() option, then following a restart, syslog-ng PE will look for or create disk-buffer files in their old location. To ensure that syslog-ng PE uses the new dir() setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.

disk-buf-size()
Type: number [bytes]
Default:

Description: This is a required option. The maximum size of the disk-buffer file in bytes. The minimum value is 1048576 bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old log-disk-fifo-size() option.
mem-buf-length()
Type: number [messages]
Default: 10000
Description: Use this option if the option reliable() is set to no. This option contains the number of messages stored in overflow queue. It replaces the old log-fifo-size() option. It inherits the value of the global log-fifo-size() option if provided. If it is not provided, the default value is 10000 messages. Note that this option will be ignored if the option reliable() is set to yes.
mem-buf-size()
Type: number [bytes]
Default: 163840000
Description: Use this option if the option reliable() is set to yes. This option contains the size of the messages in bytes that is used in the memory part of the disk-buffer file. It replaces the old log-fifo-size() option. It does not inherit the value of the global log-fifo-size() option, even if it is provided. Note that this option will be ignored if the option reliable() is set to no.
qout-size()
Type: number [messages]
Default: 64
Description: The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer file already exists, the change will take effect when the disk-buffer file becomes empty.

Options reliable() and disk-buf-size() are required options.

Example: Examples for using disk-buffer()

In the following case reliable disk-buffer() is used.

destination d_demo {
    network("127.0.0.1"
        port(3333)
        disk-buffer(
            mem-buf-size(10000)
            disk-buf-size(2000000)
            reliable(yes)
            dir("/tmp/disk-buffer")
        )
    );
};

In the following case normal disk-buffer() is used.

destination d_demo {
    network("127.0.0.1"
        port(3333)
        disk-buffer(
            mem-buf-length(10000)
            disk-buf-size(2000000)
            reliable(no)
            dir("/tmp/disk-buffer")
        )
    );
};
headers()
Type: string list
Default:

Description: Custom HTTP headers to include in the request, for example, headers("HEADER1: header1", "HEADER2: header2"). If not set, only the default headers are included, but no custom headers.

The following headers are included by default:

  • X-Syslog-Host: <host>

  • X-Syslog-Program: <program>

  • X-Syslog-Facility: <facility>

  • X-Syslog-Level: <loglevel/priority>

hook-commands()

Description: This option makes it possible to execute external programs when the relevant driver is initialized or torn down. The hook-commands() can be used with all source and destination drivers with the exception of the usertty() and internal() drivers.

NOTE: The syslog-ng PE application must be able to start and restart the external program, and have the necessary permissions to do so. For example, if your host is running AppArmor or SELinux, you might have to modify your AppArmor or SELinux configuration to enable syslog-ng PE to execute external applications.

Using the hook-commands() when syslog-ng PE starts or stops

To execute an external program when syslog-ng PE starts or stops, use the following options:

startup()
Type: string
Default: N/A

Description: Defines the external program that is executed when syslog-ng PE starts.

shutdown()
Type: string
Default: N/A

Description: Defines the external program that is executed when syslog-ng PE stops.

Using the hook-commands() when syslog-ng PE reloads

To execute an external program when the syslog-ng PE configuration is initiated or torn down (for example, on startup/shutdown or during a syslog-ng PE reload), use the following options:

setup()
Type: string
Default: N/A

Description: Defines an external program that is executed when the syslog-ng PE configuration is initiated, for example, on startup or during a syslog-ng PE reload.

teardown()
Type: string
Default: N/A

Description: Defines an external program that is executed when the syslog-ng PE configuration is stopped or torn down, for example, on shutdown or during a syslog-ng PE reload.

Example: Using the hook-commands() with a network source

In the following example, the hook-commands() is used with the network() driver and it opens an iptables port automatically when syslog-ng PE is started/stopped.

The assumption in this example is that the LOGCHAIN chain is part of a larger ruleset that routes traffic to it. Whenever the syslog-ng PE created rule is there, packets can flow (otherwise the port is closed).

source {
   network(transport(udp)
	hook-commands(
          startup("iptables -I LOGCHAIN 1 -p udp --dport 514 -j ACCEPT")
          shutdown("iptables -D LOGCHAIN 1")
        )
     );
};
key-file()
Accepted values: Filename
Default: none

Description: Path and name of a file that contains a private key in PEM format, suitable as a TLS key. If properly configured, the syslog-ng PE application uses this private key and the matching certificate (set in the cert-file() option) to authenticate the syslog-ng PE client on the destination server.

The sentinel() destination supports only unencrypted key files (that is, the private key cannot be password-protected).

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
log-fifo-size()
Type: number
Default: Use global setting.

Description: The number of messages that the output queue can store.

log-type()
Type: Microsoft Azure Sentinel parameter and an optional syslog-ng PE configuration option
Default: Syslog_CL for syslog-ng PE

Description:

On the Microsoft Azure Sentinel user interface, you can filter log events by referring to log-type parameters. Although the log-type parameters query information with their custom query language (namely, Kusto), they are essentially table fields in a database.

The log-type parameter is mandatory for the Microsoft Azure Sentinel HTTP Data Collector API interface, and for syslog-ng Premium Edition, its default value is Syslog_CL.

NOTE: While Microsoft Azure Sentinel accepts log events from external sources, it also has built-in log types. To differentiate external and built-in log types, Azure Sentinel automatically applies the Custom Log-type (_CL) suffix to log events that originate from external sources. Although the log-type parameter is optional (unlike workspace-id and auth-secret, which are mandatory), keep in mind that Microsoft Azure Sentinel will automatically attach the _CL suffix to all log events originating from external sources. For example, log events that originate from syslog-ng PE will be named Syslog_CL by default.

For more information, see Getting the required credentials to configure syslog-ng PE as a Data Connector for Microsoft Azure Sentinel and Log types.

method()
Type: POST | PUT
Default: POST

Description: Specifies the HTTP method to use when sending the message to the server.

password()
Type: string
Default:

Description: The password that syslog-ng PE uses to authenticate on the server where it sends the messages.

peer-verify()
Accepted values: yes | no
Default: yes

Description: Verification method of the peer. The following table summarizes the possible options and their results depending on the certificate of the peer.

The remote peer has:
no certificate invalid certificate valid certificate
Local peer-verify() setting no (optional-untrusted) TLS-encryption TLS-encryption TLS-encryption
yes (required-trusted) rejected connection rejected connection TLS-encryption

For untrusted certificates only the existence of the certificate is checked, but it does not have to be valid — syslog-ng accepts the certificate even if it is expired, signed by an unknown CA, or its CN and the name of the machine mismatches.

Caution:

When validating a certificate, the entire certificate chain must be valid, including the CA certificate. If any certificate of the chain is invalid, syslog-ng PE will reject the connection.

persist-name()
Type: string
Default:

None

Description:If you receive the following error message during syslog-ng PE startup, set the persist-name() option of the duplicate drivers:

Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down.

This error occurs if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the persist-name() of the drivers to a custom string, for example, persist-name("example-persist-name1").

retries()
Type: number [of attempts]
Default: 3

Description: The number of times syslog-ng PE attempts to send a message to this destination. If syslog-ng PE could not send a message, it will try again until the number of attempts reaches retries, then drops the message.

To handle HTTP error responses, if the HTTP server returns 5xx codes, syslog-ng PE will attempt to resend messages until the number of attempts reaches retries. If the HTTP server returns 4xx codes, syslog-ng PE will drop the messages.

ssl-version()
Type: string
Default: None, uses the libcurl default

Description: Specifies the permitted SSL/TLS version. Possible values: sslv2, sslv3, tlsv1, tlsv1_0, tlsv1_1, tlsv1_2.

An alternative way to specify this option is to put it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. If you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

Declaration
destination d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher")
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};
template()
Type: string
Default: A format conforming to the default logfile format.

Description: Specifies a template defining the logformat to be used in the destination. Macros are described in Macros of syslog-ng PE. Please note that for network destinations it might not be appropriate to change the template as it changes the on-wire format of the syslog protocol which might not be tolerated by stock syslog receivers (like syslogd or syslog-ng itself). For network destinations make sure the receiver can cope with the custom format defined.

throttle()
Type: number
Default: 0

Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using the disk-buffer option as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

timeout()
Type: number [seconds]
Default: 0

Description: The value (in seconds) to wait for an operation to complete, and attempt to reconnect the server if exceeded. By default, the timeout value is 0, meaning that there is no timeout. Available in version 7.0.4 and later.

url()
Type: URL or list of URLs
Default: http://localhost/

Description: Specifies the hostname or IP address, and optionally the port number of the web service that can receive log data through HTTP. Use a colon (:) after the address to specify the port number of the server. For example: http://127.0.0.1:8000

In case the server on the specified URL returns a redirect request, syslog-ng PE automatically follows maximum 3 redirects. Only HTTP-based and HTTPS-based redirections are supported.

Starting with version 7.0.12, you can specify multiple URLs, for example, url("site1", "site2"). In this case, syslog-ng PE sends log messages to the specified URLs in a load-balance fashion. This means that syslog-ng PE sends each message to only one URL. For example, you can use this to send the messages to a set of ingestion nodes or indexers of your SIEM solution if a single node cannot handle the load. Note that the order of the messages as they arrive on the servers can differ from the order syslog-ng PE has received them, so use load-balancing only if your server can use the timestamp from the messages. If the server uses the timestamp when it receives the messages, the order of the messages will be incorrect.

Caution:

If you set multiple URLs in the url() option, set the persist-name() option as well to avoid data loss.

user-agent()
Type: string
Default: syslog-ng [version]/libcurl[version]

Description: The value of the USER-AGENT header in the messages sent to the server.

user()
Type: string
Default:

Description: The username that syslog-ng PE uses to authenticate on the server where it sends the messages.

use-system-cert-store()
Type: yes | no
Default: no

Description: Use the certificate store of the system for verifying HTTPS certificates. For details, see the curl documentation.

workers()
Type: integer
Default: 1

Description: Specifies the number of worker threads (at least 1) that syslog-ng PE uses to send messages to the server. Increasing the number of worker threads can drastically improve the performance of the destination.

Caution:

Hazard of data loss. When you use more than one worker threads together with the disk-buffer option, syslog-ng PE creates a separate disk-buffer file for each worker thread. This means that decreasing the number of workers can result in losing data currently stored in the disk-buffer files. Do not decrease the number of workers when the disk-buffer files are in use.

If you are using load-balancing (that is, you have configured multiple servers in the url() option), increase the number of worker threads at least to the number of servers. For example, if you have set three URLs (url("site1", "site2", "site3")), set the workers() option to 3 or more.

workspace-id()
Type: Provided by Microsoft: unique hexadecimal number, identifying your Sentinel instance. On the syslog-ng PE side, it is handled as string.
Default: N/A

Description: A unique option for syslog-ng PE's sentinel() destination. This parameter is required so that syslog-ng PE can authenticate to Microsoft servers. You can collect the required credentials on your Microsoft Azure Sentinel Workspace.

For more information, see Getting the required credentials to configure syslog-ng PE as a Data Connector for Microsoft Azure Sentinel.

smtp: Generating SMTP messages (email) from logs

The destination is aimed at a fully controlled local, or near-local, trusted SMTP server. The goal is to send mail to trusted recipients, through a controlled channel. It hands mails over to an SMTP server, and that is all it does, therefore the resulting solution is as reliable as sending an email in general. For example, syslog-ng PE does not verify whether the recipient exists.

The smtp() driver sends email messages triggered by log messages. The smtp() driver uses SMTP, without needing external applications. You can customize the main fields of the email, add extra headers, send the email to multiple recipients, and so on.

The subject(), body(), and header() fields may include macros which get expanded in the email. For more information on available macros see Macros of syslog-ng PE.

The smtp() driver has the following required parameters: host(), port(), from(), to(), subject(), and body(). For the list of available optional parameters, see smtp() destination options.

NOTE: To use this destination, syslog-ng PE must run in server mode. Typically, only the central syslog-ng PE server uses this destination. For more information on the server mode, see Server mode.

NOTE:

The smtp() destination driver is available only in 5 F2 and later.

Declaration
smtp(host() port() from() to() subject() body() options());
Example: Using the smtp() driver

The following example defines an smtp() destination using only the required parameters.

destination d_smtp {
    smtp(
        host("localhost")
        port(25)
        from("syslog-ng alert service" "noreply@example.com")
        to("Admin #1" "admin1@example.com")
        subject("[ALERT] Important log message of $LEVEL condition received from $HOST/$PROGRAM!")
        body("Hi!\nThe syslog-ng alerting service detected the following important log message:\n $MSG\n-- \nsyslog-ng\n")
    );
};

The following example sets some optional parameters as well.

destination d_smtp {
    smtp(
        host("localhost")
        port(25)
        from("syslog-ng alert service" "noreply@example.com")
        to("Admin #1" "admin1@example.com")
        to("Admin #2" "admin2@example.com")
        cc("Admin BOSS" "admin.boss@example.com")
        bcc("Blind CC" "blindcc@example.com")
        subject("[ALERT] Important log message of $LEVEL condition received from $HOST/$PROGRAM!")
        body("Hi!\nThe syslog-ng alerting service detected the following important log message:\n $MSG\n-- \nsyslog-ng\n")
        header("X-Program", "$PROGRAM")
    );
};
Example: Simple email alerting with the smtp() driver

The following example sends an email alert if the eth0 network interface of the host is down.

filter f_linkdown {
    match("eth0: link down" value("MESSAGE"));
};
destination d_alert {
    smtp(
        host("localhost") port(25)
        from("syslog-ng alert service" "syslog@localhost")
        reply-to("Admins" "root@localhost")
        to("Ennekem" "me@localhost")
        subject("[SYSLOG ALERT]: eth0 link down")
        body("Syslog received an alert:\n$MSG")
    );
};

log {
    source(s_local);
    filter(f_linkdown);
    destination(d_alert);
};

smtp() destination options

The smtp() sends email messages using SMTP, without needing external applications. The smtp() destination has the following options:

body()
Type: string
Default: n/a

Description: The BODY field of the email. You can also use macros in the string. Use \n to start a new line. For example:

body("syslog-ng PE received the following alert from $HOST:\n$MSG")
bcc()
Type: string
Default: n/a

Description: The BCC recipient of the email (contents of the BCC field). You can specify the email address, or the name and the email address. Set the bcc() option multiple times to send the email to multiple recipients. For example: bcc("admin@example.com") or bcc("Admin" "admin@example.com") or bcc("Admin" "admin@example.com") bcc("Admin2" "admin2@example.com")

You can also use macros to set the value of this parameter.

cc()
Type: string
Default: n/a

Description: The CC recipient of the email (contents of the CC field). You can specify the email address, or the name and the email address. Set the cc() option multiple times to send the email to multiple recipients. For example: cc("admin@example.com") or cc("Admin" "admin@example.com") or cc("Admin" "admin@example.com") cc("Admin2" "admin2@example.com")

You can also use macros to set the value of this parameter.

disk-buffer()

Description: This option enables putting outgoing messages into the disk-buffer file of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:

reliable()
Type: yes|no
Default: no

Description: If set to yes, syslog-ng PE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng PE crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no, the normal disk-buffer option will be used. This provides a faster, but less reliable disk-buffer option.

Caution:

Hazard of data loss! If you change the value of reliable() option when there are messages in the disk-buffer file, the messages stored in the disk-buffer file will be lost.

dir()
Type: string
Default: N/A

Description: Defines the folder where the disk-buffer files are stored.

Note that changing the value the dir() option will not move or copy existing files from the old directory to the new one.

Caution:

When creating a new dir() option for a disk-buffer file, or modifying an existing one, make sure you delete the persist file.

syslog-ng PE creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir() option, then following a restart, syslog-ng PE will look for or create disk-buffer files in their old location. To ensure that syslog-ng PE uses the new dir() setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.

disk-buf-size()
Type: number [bytes]
Default:

Description: This is a required option. The maximum size of the disk-buffer file in bytes. The minimum value is 1048576 bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old log-disk-fifo-size() option.
mem-buf-length()
Type: number [messages]
Default: 10000
Description: Use this option if the option reliable() is set to no. This option contains the number of messages stored in overflow queue. It replaces the old log-fifo-size() option. It inherits the value of the global log-fifo-size() option if provided. If it is not provided, the default value is 10000 messages. Note that this option will be ignored if the option reliable() is set to yes.
mem-buf-size()
Type: number [bytes]
Default: 163840000
Description: Use this option if the option reliable() is set to yes. This option contains the size of the messages in bytes that is used in the memory part of the disk-buffer file. It replaces the old log-fifo-size() option. It does not inherit the value of the global log-fifo-size() option, even if it is provided. Note that this option will be ignored if the option reliable() is set to no.
qout-size()
Type: number [messages]
Default: 64
Description: The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer file already exists, the change will take effect when the disk-buffer file becomes empty.

Options reliable() and disk-buf-size() are required options.

Example: Examples for using disk-buffer()

In the following case reliable disk-buffer() is used.

destination d_demo {
    network("127.0.0.1"
        port(3333)
        disk-buffer(
            mem-buf-size(10000)
            disk-buf-size(2000000)
            reliable(yes)
            dir("/tmp/disk-buffer")
        )
    );
};

In the following case normal disk-buffer() is used.

destination d_demo {
    network("127.0.0.1"
        port(3333)
        disk-buffer(
            mem-buf-length(10000)
            disk-buf-size(2000000)
            reliable(no)
            dir("/tmp/disk-buffer")
        )
    );
};
from()
Type: string
Default: n/a

Description: The sender of the email (contents of the FROM field). You can specify the email address, or the name and the email address. For example:

from("admin@example.com")
or
from("Admin" "admin@example.com")

If you specify the from() option multiple times, the last value will be used. Instead of the from() option, you can also use sender(), which is just an alias of the from() option.

You can also use macros to set the value of this parameter.

header()
Type: string
Default: n/a

Description: Adds an extra header to the email with the specified name and content. The first parameter sets the name of the header, the second one its value. The value of the header can contain macros. Set the header() option multiple times to add multiple headers. For example:

header("X-Program", "$PROGRAM")

When using the header option, note the following points:

  • Do not use the header() option to set the values of headers that have dedicated options. Use it only to add extra headers.

  • If you set the same custom header multiple times, only the first will be added to the email, other occurrences will be ignored.

  • It is not possible to set the DATE, Return-Path, Original-Recipient, Content-*, MIME-*, Resent-*, Received headers.

host()
Type: hostname or IP address
Default: n/a

Description: Hostname or IP address of the SMTP server.

NOTE:

If you specify host="localhost", syslog-ng PE will use a socket to connect to the local SMTP server. Use host="127.0.0.1" to force TCP communication between syslog-ng PE and the local SMTP server.

log-fifo-size()
Type: number
Default: Use global setting.

Description: The number of messages that the output queue can store.

port()
Type: number
Default: 25

Description: The port number of the SMTP server.

reply-to()
Type: string
Default: n/a

Description: Replies of the recipient will be sent to this address (contents of the REPLY-TO field). You can specify the email address, or the name and the email address. Set the reply-to() option multiple times to send the email to multiple recipients. For example: reply-to("admin@example.com") or reply-to("Admin" "admin@example.com") or reply-to("Admin" "admin@example.com") reply-to("Admin2" "admin2@example.com")

You can also use macros to set the value of this parameter.

retries()
Type: number [of attempts]
Default: 3

Description: The number of times syslog-ng PE attempts to send a message to this destination. If syslog-ng PE could not send a message, it will try again until the number of attempts reaches retries, then drops the message.

subject()
Type: string
Default: n/a

Description: The SUBJECT field of the email. You can also use macros. For example:

subject("[SYSLOG ALERT]: Critical error message received from $HOST")

If you specify the subject() option multiple times, the last value will be used.

throttle()
Type: number
Default: 0

Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using the disk-buffer option as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

to()
Type: string
Default: localhost

Description: The recipient of the email (contents of the TO field). You can specify the email address, or the name and the email address. Set the to() option multiple times to send the email to multiple recipients. For example: to("admin@example.com") or to("Admin" "admin@example.com") or to("Admin" "admin@example.com") to("Admin2" "admin2@example.com")

You can also use macros to set the value of this parameter.

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