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syslog-ng Premium Edition 6.0.18 - Administration Guide

Preface Chapter 1. Introduction to syslog-ng Chapter 2. The concepts of syslog-ng Chapter 3. Installing syslog-ng Chapter 4. The syslog-ng PE quick-start guide Chapter 5. The syslog-ng PE configuration file Chapter 6. Collecting log messages — sources and source drivers Chapter 7. Sending and storing log messages — destinations and destination drivers Chapter 8. Routing messages: log paths, reliability, and filters Chapter 9. Global options of syslog-ng PE Chapter 10. TLS-encrypted message transfer Chapter 11. FIPS-compliant syslog-ng Chapter 12.  Reliable Log Transfer Protocol™ Chapter 13. Reliability and minimizing the loss of log messages Chapter 14. Manipulating messages Chapter 15. Parsing and segmenting structured messages Chapter 16. Processing message content with a pattern database Chapter 17. Statistics and metrics of syslog-ng Chapter 18. Multithreading and scaling in syslog-ng PE Chapter 19. Troubleshooting syslog-ng Chapter 20. Best practices and examples

Chapter 9. Global options of syslog-ng PE

Configuring global syslog-ng options

The syslog-ng application has a number of global options governing DNS usage, the timestamp format used, and other general points. Each option may have parameters, similarly to driver specifications. To set global options, add an option statement to the syslog-ng configuration file using the following syntax:

options { option1(params); option2(params); ... };

Example 9.1. Using global options

To disable domain name resolving, add the following line to the syslog-ng configuration file:

options { use-dns(no); };

For a detailed list of the available options, see the section called “Global options”. For important global options and recommendations on their use, see Chapter 20, Best practices and examples.

Global options

The following options can be specified in the options statement, as described in the section called “Configuring global syslog-ng options”.

bad-hostname()
Accepted values: regular expression
Default: no

Description: A regexp containing hostnames which should not be handled as hostnames.

chain-hostnames()
Accepted values: yes | no
Default: no

Description: Enable or disable the chained hostname format. If a client sends the log message directly to the syslog-ng PE server, the chain-hostnames() option is enabled on the server, and the client sends a hostname in the message that is different from its DNS hostname (as resolved from DNS by the syslog-ng PE server), then the server can append the resolved hostname to the hostname in the message (separated with a / character) when the message is written to the destination.

For example, consider a client-server scenario with the following hostnames: client-hostname-from-the-message, client-hostname-resolved-on-the-server, server-hostname. The hostname of the log message written to the destination depends on the keep-hostname() and the chain-hostnames() options. How keep-hostname() and chain-hostnames() options are related is described in the following table.

keep-hostname() setting on the server
yes no
chain-hostnames() setting on the server yes client-hostname-from-the-message client-hostname-from-the-message / client-hostname-resolved-on-the-server
no client-hostname-from-the-message client-hostname-resolved-on-the-server

If the log message is forwarded to the syslog-ng PE server via a syslog-ng PE relay, the hostname depends on the settings of the keep-hostname() and the chain-hostnames() options both on the syslog-ng PE relay and the syslog-ng PE server.

For example, consider a client-relay-server scenario with the following hostnames: client-hostname-from-the-message, client-hostname-resolved-on-the-relay, client-hostname-resolved-on-the-server, relay-hostname-resolved-on-the-server. How keep-hostname() and chain-hostnames() options are related is described in the following table.

chain-hostnames() setting on the server
yes no
keep-hostname() setting on the server keep-hostname() setting on the server
yes no yes no
chain- hostnames() setting on the relay yes keep- hostname() setting on the relay yes client-hostname- from-the-message client-hostname- from-the-message / relay-hostname- resolved-on-the- server client-hostname- from-the-message relay-hostname- resolved-on-the- server
no client-hostname- from-the-message / client-hostname- resolved-on-the- relay client-hostname- from-the-message / client-hostname- resolved-on-the- relay / relay- hostname-resolved- on-the-server client-hostname- from-the-message / client-hostname- resolved-on-the- relay
no keep- hostname() setting on the relay yes client-hostname- from-the-message client-hostname- from-the-message / relay-hostname- resolved-on-the- server client-hostname- from-the-message
no client-hostname- resolved-on-the- relay client-hostname- resolved-on-the- relay / relay- hostname-resolved- on-the-server client-hostname- resolved-on-the- relay

The chain-hostnames() option of syslog-ng can interfere with the way syslog-ng PE counts the log source hosts, causing syslog-ng to think there are more hosts logging to the central server, especially if the clients sends a hostname in the message that is different from its real hostname (as resolved from DNS). Disable the chain-hostnames() option on your log sources to avoid any problems related to license counting.

check-hostname()
Accepted values: yes | no
Default: no

Description: Enable or disable checking whether the hostname contains valid characters.

create-dirs()
Accepted values: yes | no
Default: no

Description: Enable or disable directory creation for destination files.

custom-domain()
Accepted values: string
Default: empty string

Description: Use this option to specify a custom domain name that is appended after the short hostname to receive the FQDN. This option affects every outgoing message: eventlog sources, file sources, MARK messages and internal messages of syslog-ng PE.

  • If the hostname is a short hostname, the custom domain name is appended after the hostname (for example mypc becomes mypc.customcompany.local).

  • If the hostname is an FQDN, the domain name part is replaced with the custom domain name (for example if the FQDN in the forwarded message is mypc.mycompany.local and the custom domain name is customcompany.local, the hostname in the outgoing message becomes mypc.customcompany.local).

dir-group()
Accepted values: groupid
Default: root

Description: The default group for newly created directories.

dir-owner()
Accepted values: userid
Default: root

Description: The default owner of newly created directories.

dir-perm()
Accepted values: permission value
Default: 0700

Description: The permission mask of directories created by syslog-ng. Log directories are only created if a file after macro expansion refers to a non-existing directory, and directory creation is enabled (see also the create-dirs() option). For octal numbers prefix the number with 0, for example use 0755 for rwxr-xr-x.

To preserve the original properties of an existing directory, use the option without specifying an attribute: dir-perm(). Note that when creating a new directory without specifying attributes for dir-perm(), the default permission of the directories is masked with the umask of the parent process (typically 0022).

dns-cache()
Accepted values: yes | no
Default: yes

Description: Enable or disable DNS cache usage.

NOTE:

This option has no effect if the keep-hostname() option is enabled (keep-hostname(yes)) and the message contains a hostname.

dns-cache-expire()
Accepted values: number (seconds)
Default: 3600

Description: Number of seconds while a successful lookup is cached.

dns-cache-expire-failed()
Accepted values: number (seconds)
Default: 60

Description: Number of seconds while a failed lookup is cached.

dns-cache-hosts()
Accepted values: filename
Default: unset

Description: Name of a file in /etc/hosts format that contains static IP->hostname mappings. Use this option to resolve hostnames locally without using a DNS. Note that any change to this file triggers a reload in syslog-ng and is instantaneous.

dns-cache-size()
Accepted values: number of hostnames
Default: 1007

Description: Number of hostnames in the DNS cache.

file-template()
Accepted values: string
Default:

Description: Specifies a template that file-like destinations use by default. For example:

template t_isostamp { template("$ISODATE $HOST $MSGHDR$MSG\n"); };

options { file-template(t_isostamp); };
flush-lines()
Accepted values: number (messages)
Default: 1

Description: Specifies how many lines are flushed to a destination at a time. The syslog-ng PE application waits for this number of lines to accumulate and sends them off in a single batch. Setting this number high increases throughput as fully filled frames are sent to the network, but also increases message latency.

flush-timeout() (OBSOLETE)

Accepted values: time in milliseconds
Default: 10000

Description: This is an obsolete option. Specifies the time syslog-ng waits for lines to accumulate in its output buffer. For details, see the flush-lines() option.

NOTE:

This option will be removed from the list of acceptable options. After that, your configuration will become invalid if it still contains the flush-timeout() option. To avoid future problems, remove this option from your configuration.

frac-digits()
Type: number (digits of fractions of a second)
Default: Value of the global option (which defaults to 0)

Description: The syslog-ng application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received. Note that syslog-ng can add the fractions to non-ISO8601 timestamps as well.

group()
Accepted values: groupid
Default: root

Description: The default group of output files. By default, syslog-ng changes the privileges of accessed files (for example /dev/null) to root.root 0600. To disable modifying privileges, use this option with the -1 value.

keep-hostname()
Type: yes or no
Default: no

Description: Enable or disable hostname rewriting.

  • If enabled (keep-hostname(yes)), syslog-ng PE assumes that the incoming log message was sent by the host specified in the HOST field of the message.

  • If disabled (keep-hostname(no)), syslog-ng PE rewrites the HOST field of the message, either to the IP address (if the use-dns() parameter is set to no), or to the hostname (if the use-dns() parameter is set to yes and the IP address can be resolved to a hostname) of the host sending the message to syslog-ng PE. For details on using name resolution in syslog-ng PE, see the section called “Using name resolution in syslog-ng”.

NOTE:

If the log message does not contain a hostname in its HOST field, syslog-ng PE automatically adds a hostname to the message.

  • For messages received from the network, this hostname is the address of the host that sent the message (this means the address of the last hop if the message was transferred via a relay).

  • For messages received from the local host, syslog-ng PE adds the name of the host.

This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

NOTE:

When relaying messages, enable this option on the syslog-ng PE server and also on every relay, otherwise syslog-ng PE will treat incoming messages as if they were sent by the last relay.

keep-timestamp()
Type: yes or no
Default: yes

Description: Specifies whether syslog-ng should accept the timestamp received from the sending application or client. If disabled, the time of reception will be used instead. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

Caution:

To use the S_ macros, the keep-timestamp() option must be enabled (this is the default behavior of syslog-ng PE).

log-fifo-size()
Accepted values: number (messages)
Default: 10000

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

log-msg-size()
Accepted values: number (bytes)
Default: 65535

Description: Maximum length of a message in bytes. This length includes the entire message (the data structure and individual fields). The maximal value that can be set is 268435456 bytes (256MB). For messages using the IETF-syslog message format (RFC5424), the maximal size of the value of an SDATA field is 64kB.

logstore-journal-shmem-threshold()
Type: number (bytes)
Default: 536870912

Description: If the size of memory (in bytes) required by journal files increases above this value, syslog-ng PE maps only a single block of every logstore journal into the memory. Default value: 536870912 (512 MB).

If the memory required for the journal files exceeds the logstore-journal-shmem-threshold() limit, syslog-ng PE will store only a single journal block of every journal file in the memory, and — if more blocks are needed for a journal — store the additional blocks on the hard disk. Opening new logstore files means allocating memory for one new journal block for every new file. In extreme situations involving large traffic, this can lead to syslog-ng PE consuming the entire memory of the system. Adjust the journal-block-size() and your file-naming conventions as needed to avoid such situations. For details on logstore journals, see the section called “Journal files”.

Example 9.2. Calculating memory usage of logstore journals

If you are using the default settings (4 journal blocks for every logstore journal, one block is 1MB, logstore-journal-shmem-threshold() is 512MB), this means that syslog-ng PE will allocate 4MB memory for every open logstore file, up to 512MB if you have 128 open logstore files. Opening a new logstore file would require 4 more megabytes of memory for journaling, bringing the total required memory to 516MB, which is above the logstore-journal-shmem-threshold(). In this case, syslog-ng PE switches to storing only a single journal block in the memory, lowering the memory requirements of journaling to 129MB. However, opening more and more logstore files will require more and more memory, and this is not limited, except when syslog-ng PE reaches the maximum number of files that can be open (as set in the --fd-limit command-line option).


Example 9.3. Limiting the memory use of journal files

The following example causes syslog-ng PE to map only a single journal block into the host's memory if the total memory range used by logstore journals would be higher than 32 MB.

options {
    logstore-journal-shmem-threshold(33554432);
};
destination d_messages { logstore("/var/log/messages_logstore.lgs"
                         journal-block-size(19660800)
                         journal-block-count(5)
                         );
};

mark() (DEPRECATED)

Accepted values: number (seconds)
Default: 1200

Description: The mark-freq() option is an alias for the deprecated mark() option. This is retained for compatibility with syslog-ng version 1.6.x.

mark-freq()
Accepted values: number (seconds)
Default: 1200

Description: An alias for the obsolete mark() option, retained for compatibility with syslog-ng version 1.6.x. The number of seconds between two MARK messages. MARK messages are generated when there was no message traffic to inform the receiver that the connection is still alive. If set to zero (0), no MARK messages are sent. The mark-freq() can be set for global option and/or every MARK capable destination driver if mark-mode() is periodical or dst-idle or host-idle. If mark-freq() is not defined in the destination, then the mark-freq() will be inherited from the global options. If the destination uses internal mark-mode(), then the global mark-freq() will be valid (does not matter what mark-freq() set in the destination side).

mark-mode()
Accepted values: internal | dst-idle | host-idle | periodical | none | global
Default:

internal for pipe, program drivers

none for file, unix-dgram, unix-stream drivers

global for syslog, tcp, udp destinations

host-idle for global option

Description: The mark-mode() option can be set for the following destination drivers: file(), program(), unix-dgram(), unix-stream(), network(), pipe(), syslog() and in global option.

  • internal: When internal mark mode is selected, internal source should be placed in the log path as this mode does not generate mark by itself at the destination. This mode only yields the mark messages from internal source. This is the mode as syslog-ng PE 3.x worked. MARK will be generated by internal source if there was NO traffic on local sources:

    file(), pipe(), unix-stream(), unix-dgram(), program()

  • dst-idle: Sends MARK signal if there was NO traffic on destination drivers. MARK signal from internal source will be dropped.

    MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

  • host-idle: Sends MARK signal if there was NO local message on destination drivers. For example MARK is generated even if messages were received from tcp. MARK signal from internal source will be dropped.

    MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

  • periodical: Sends MARK signal perodically, regardless of traffic on destination driver. MARK signal from internal source will be dropped.

    MARK signal can be sent by the following destination drivers: network(), syslog(), program(), file(), pipe(), unix-stream(), unix-dgram().

  • none: Destination driver drops all MARK messages. If an explicit mark-mode() is not given to the drivers where none is the default value, then none will be used.

  • global: Destination driver uses the global mark-mode() setting. The syslog-ng interprets syntax error if the global mark-mode() is global.

NOTE:

In case of dst-idle, host-idle and periodical, the MARK message will not be written in the destination, if it is not open yet.

Available in syslog-ng PE 4 LTS and later.

normalize-hostnames()
Accepted values: yes | no
Default: no

Description: If enabled (normalize-hostnames(yes)), syslog-ng PE converts the hostnames to lowercase.

NOTE:

This setting applies only to hostnames resolved from DNS. It has no effect if the keep-hostname() option is enabled, and the message contains a hostname.

on-error()
Accepted values: drop-message|drop-property|fallback-to-string|silently-drop-message|silently-drop-property|silently-fallback-to-string
Default: drop-message

Description: Controls what happens when type-casting fails and syslog-ng PE cannot convert some data to the specified type. By default, syslog-ng PE drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

  • drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of syslog-ng PE.

  • drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.

  • fallback-to-string: Convert the property to string and log an error message to the internal() source.

  • silently-drop-message: Drop the entire message silently, without logging the error.

  • silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.

  • silently-fallback-to-string: Convert the property to string silently, without logging the error.

owner()
Accepted values: userid
Default: root

Description: The default owner of output files. By default, syslog-ng changes the privileges of accessed files (for example /dev/null) to root.root 0600. To disable modifying privileges, use this option with the -1 value.

perm()
Accepted values: permission value
Default: 0600

Description: The default permission for output files. By default, syslog-ng changes the privileges of accessed files (for example /dev/null) to root.root 0600. To disable modifying privileges, use this option with the -1 value.

proto-template()
Accepted values: name of a template
Default: The default message format of the used protocol

Description: Specifies a template that protocol-like destinations (for example, network() and syslog()) use by default. For example:

template t_isostamp { template("$ISODATE $HOST $MSGHDR$MSG\n"); };

options { proto-template(t_isostamp); };
recv-time-zone()
Accepted values: name of the timezone, or the timezone offset
Default: local timezone

Description: Specifies the time zone associated with the incoming messages, if not specified otherwise in the message or in the source driver. For details, see also the section called “Timezones and daylight saving” and the section called “A note on timezones and timestamps”.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

send-time-zone()
Accepted values: name of the timezone, or the timezone offset
Default: local timezone

Description: Specifies the time zone associated with the messages sent by syslog-ng, if not specified otherwise in the message or in the destination driver. For details, see the section called “Timezones and daylight saving”.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

stats-freq()
Accepted values: number (seconds)
Default: 600

Description: The period between two STATS messages in seconds. STATS are log messages sent by syslog-ng, containing statistics about dropped log messages. Set to 0 to disable the STATS messages.

stats-level()
Accepted values: 0 | 1 | 2 | 3
Default: 0

Description: Specifies the detail of statistics syslog-ng collects about the processed messages.

  • Level 0 collects only statistics about the sources and destinations

  • Level 1 contains details about the different connections and log files, but has a slight memory overhead

  • Level 2 contains detailed statistics based on the hostname.

  • Level 3 contains detailed statistics based on various message parameters like facility, severity, or tags.

Note that level 2 and 3 increase the memory requirements and CPU load. For details on message statistics, see Chapter 17, Statistics and metrics of syslog-ng.

sync() or sync-freq() (DEPRECATED)

Accepted values: number (messages)
Default: 0

Description: Obsolete aliases for flush-lines()

threaded()
Accepted values: yes|no
Default: yes

Description: Enable syslog-ng PE to run in multithreaded mode and use multiple CPUs. Available only in syslog-ng Premium Edition 4 F1 and later. See Chapter 18, Multithreading and scaling in syslog-ng PE for details.

time-reap()
Accepted values: number (seconds)
Default: 60

Description: The time to wait in seconds before an idle destination file is closed. Note that only destination files having macros in their filenames are closed automatically.

time-reopen()
Accepted values: number (seconds)
Default: 60

Description: The time to wait in seconds before a dead connection is reestablished.

time-sleep() (DEPRECATED)

Accepted values: number (milliseconds)
Default: 0

Description: The time to wait in milliseconds between each invocation of the poll() iteration.

timestamp-freq()
Type: number (seconds)
Default: 0

Description: The minimum time (in seconds) that should expire between two timestamping requests. When syslog-ng closes a chunk, it checks how much time has expired since the last timestamping request: if it is higher than the value set in the timestamp-freq() parameter, it requests a new timestamp from the authority set in the timestamp-url() parameter.

By default, timestamping is disabled: the timestamp-freq() global option is set to 0. To enable timestamping, set it to a positive value.

timestamp-url()
Accepted values: string
Default:

Description: The URL of the Timestamping Authority used to request timestamps to sign logstore chunks. Note that syslog-ng PE currently supports only Timestamping Authorities that conform to RFC3161 Internet X.509 Public Key Infrastructure Time-Stamp Protocol, other protocols like Microsoft Authenticode Timestamping are not supported.

timestamp-policy()
Accepted values: string
Default:

Description: If the Timestamping Server has timestamping policies configured, specify the OID of the policy to use into the Timestamping policy field. syslog-ng PE will include this ID in the timestamping requests sent to the TSA. This option is available in syslog-ng PE 3.1 and later.

time-zone()
Type: name of the timezone, or the timezone offset
Default: unspecified

Description: Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, HOUR. For the complete list of such macros, see the section called “Date-related macros”.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

ts-format()
Accepted values: rfc3164 | bsd | rfc3339 | iso
Default: rfc3164

Description: Specifies the timestamp format used when syslog-ng itself formats a timestamp and nothing else specifies a format (for example: STAMP macros, internal messages, messages without original timestamps). For details, see also the section called “A note on timezones and timestamps”.

By default, timestamps include only seconds. To include fractions of a second (for example, milliseconds) use the frac-digits() option. For details, see the section called “frac-digits()”.

NOTE:

This option applies only to file and file-like destinations. Destinations that use specific protocols (for example, network(), or syslog()) ignore this option. For protocol-like destinations, use a template locally in the destination, or use the proto-template option.

use-dns()
Type: yes, no, persist_only
Default: yes

Description: Enable or disable DNS usage. The persist_only option attempts to resolve hostnames locally from file (for example from /etc/hosts). The syslog-ng PE application blocks on DNS queries, so enabling DNS may lead to a Denial of Service attack. To prevent DoS, protect your syslog-ng network endpoint with firewall rules, and make sure that all hosts which may get to syslog-ng are resolvable. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

NOTE:

This option has no effect if the keep-hostname() option is enabled (keep-hostname(yes)) and the message contains a hostname.

use-fqdn()
Type: yes or no
Default: no

Description: Add Fully Qualified Domain Name instead of short hostname. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.

NOTE:

This option has no effect if the keep-hostname() option is enabled (keep-hostname(yes)) and the message contains a hostname.

use-rcptid() (DEPRECATED)

Accepted values: yes | no
Default: no

Description: The receipt ID function is disabled by default due to performance issues. For details, see also the section called “RCPTID”. This function is now deprecated. Use the use-uniqid() option instead, for details, see the section called “use-uniqid()”.

use-time-recvd() (DEPRECATED)

Accepted values: yes | no
Default: no

Caution:

This option is not available in syslog-ng PE version 3.2 and later. Use the R_ prefixed version of the respective macro instead. Starting with syslog-ng PE version 3.2, the DATE macro equals the S_DATE macro.

Description: This option controls how the time related macros are expanded in filename and content templates. If set to yes, then the non-prefixed versions of the time related macros (for example: HOUR instead of R_HOUR and S_HOUR) refer to the time when the message was received, otherwise it refers to the timestamp which is in the message.

NOTE:

The timestamps in the messages are generated by the originating host and might not be accurate.

This option is deprecated as many users assumed that it controls the timestamp as it is written to logfiles/destinations, which is not the case. To change how messages are formatted, specify a content-template referring to the appropriate prefixed (S_ or R_) time macro.

use-uniqid()
Accepted values: yes | no
Default: no

Description: This option enables generating a globally unique ID. It is generated from the HOSTID and the RCPTID in the format of HOSTID@RCPTID. It has a fixed length: 16+@+8 characters. You can include the unique ID in the message by using the macro. For details, see the section called “UNIQID”.

Enabling this option automatically generates the HOSTID. The HOSTID is a persistent, 32-bits-long cryptographically secure pseudo random number, that belongs to the host that the syslog-ng is running on. If the persist file is damaged, the HOSTID might change.

Enabling this option automatically enables the RCPTID functionality. For details, see the section called “RCPTID”

Chapter 10. TLS-encrypted message transfer

Secure logging using TLS

The syslog-ng application can send and receive log messages securely over the network using the Transport Layer Security (TLS) protocol using the network() and syslog() drivers.

TLS uses certificates to authenticate and encrypt the communication, as illustrated on the following figure:

Figure 10.1. Certificate-based authentication

Certificate-based authentication

The client authenticates the server by requesting its certificate and public key. Optionally, the server can also request a certificate from the client, thus mutual authentication is also possible.

In order to use TLS encryption in syslog-ng, the following elements are required:

  • A certificate on the syslog-ng server that identifies the syslog-ng server.

  • The certificate of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) must be available on the syslog-ng client.

When using mutual authentication to verify the identity of the clients, the following elements are required:

  • A certificate must be available on the syslog-ng client. This certificate identifies the syslog-ng client.

  • The certificate of the Certificate Authority that issued the certificate of the syslog-ng client must be available on the syslog-ng server.

Mutual authentication ensures that the syslog-ng server accepts log messages only from authorized clients.

For details on configuring TLS communication in syslog-ng, see the section called “Encrypting log messages with TLS”.

Encrypting log messages with TLS

This section describes how to configure TLS encryption in syslog-ng. For the concepts of using TLS in syslog-ng, see the section called “Secure logging using TLS”.

Create an X.509 certificate for the syslog-ng server.

NOTE:

The subject_alt_name parameter (or the Common Name parameter if the subject_alt_name parameter is empty) of the server's certificate must contain the hostname or the IP address (as resolved from the syslog-ng clients and relays) of the server (for example syslog-ng.example.com).

Alternatively, the Common Name or the subject_alt_name parameter can contain a generic hostname, for example *.example.com.

Note that if the Common Name of the certificate contains a generic hostname, do not specify a specific hostname or an IP address in the subject_alt_name parameter.

Procedure 10.1. Configuring TLS on the syslog-ng clients

Purpose: 

Complete the following steps on every syslog-ng client host. Examples are provided using both the legacy BSD-syslog protocol (using the network() driver) and the new IETF-syslog protocol standard (using the syslog() driver):

Steps: 

  1. Copy the CA certificate (for example cacert.pem) of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) to the syslog-ng client hosts, for example into the /opt/syslog-ng/etc/syslog-ng/ca.d directory.

    Issue the following command on the certificate: openssl x509 -noout -hash -in cacert.pem The result is a hash (for example 6d2962a8), a series of alphanumeric characters based on the Distinguished Name of the certificate.

    Note that by default, syslog-ng PE expects SHA-1 hashes. If you want to use MD5 hashes for some reason, use the ca_dir_layout(md5-based) option in your configuration (for details, see Collecting log messages from UDP sources).

    Issue the following command to create a symbolic link to the certificate that uses the hash returned by the previous command and the .0 suffix.

    ln -s cacert.pem 6d2962a8.0

  2. Add a destination statement to the syslog-ng configuration file that uses the tls( ca-dir(path_to_ca_directory) ) option and specify the directory using the CA certificate. The destination must use the network() or the syslog() destination driver, and the IP address and port parameters of the driver must point to the syslog-ng server.

    Example 10.1. A destination statement using TLS

    The following destination encrypts the log messages using TLS and sends them to the 6514/TCP port of the syslog-ng server having the 10.1.2.3 IP address.

    destination demo_tls_destination {
        network("10.1.2.3" port(6514)
            transport("tls")
            tls( ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d"))
        );
    };

    A similar statement using the IETF-syslog protocol and thus the syslog() driver:

    destination demo_tls_syslog_destination {
        syslog("10.1.2.3" port(6514)
            transport("tls")
            tls(ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d"))
        );
    };

  3. Include the destination created in Step 2 in a log statement.

    Caution:

    The encrypted connection between the server and the client fails if the Common Name or the subject_alt_name parameter of the server certificate does not contain the hostname or the IP address (as resolved from the syslog-ng clients and relays) of the server.

    Do not forget to update the certificate files when they expire.

Procedure 10.2. Configuring TLS on the syslog-ng server

Purpose: 

Complete the following steps on the syslog-ng server:

Steps: 

  1. Copy the certificate (for example syslog-ng.cert) of the syslog-ng server to the syslog-ng server host, for example into the /opt/syslog-ng/etc/syslog-ng/cert.d directory. The certificate must be a valid X.509 certificate in PEM format.

  2. Copy the private key (for example syslog-ng.key) matching the certificate of the syslog-ng server to the syslog-ng server host, for example into the /opt/syslog-ng/etc/syslog-ng/key.d directory. The key must be in PEM format, and must not be password-protected.

  3. Add a source statement to the syslog-ng configuration file that uses the tls( key-file(key_file_fullpathname) cert-file(cert_file_fullpathname) ) option and specify the key and certificate files. The source must use the source driver (network() or syslog()) matching the destination driver used by the syslog-ng client.

    Example 10.2. A source statement using TLS

    The following source receives log messages encrypted using TLS, arriving to the 1999/TCP port of any interface of the syslog-ng server.

    source demo_tls_source {
        network(ip(0.0.0.0) port(1999)
            transport("tls")
            tls( key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                 cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert"))
        );
    };

    A similar source for receiving messages using the IETF-syslog protocol:

    source demo_tls_syslog_source {
        syslog(ip(0.0.0.0) port(1999)
            transport("tls")
            tls( key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                 cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert"))
        );
    };

  4. Disable mutual authentication for the source by setting the following TLS option in the source statement: tls( peer-verify(optional-untrusted);

    For details on how to configure mutual authentication, see the section called “Mutual authentication using TLS”.

    For the details of the available tls() options, see the section called “TLS options”.

    Example 10.3. Disabling mutual authentication

    The following source receives log messages encrypted using TLS, arriving to the 1999/TCP port of any interface of the syslog-ng server. The identity of the syslog-ng client is not verified.

    source demo_tls_source {
        network(ip(0.0.0.0) port(1999)
            transport("tls")
            tls( key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                 cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert")
                 peer-verify(optional-untrusted))
        );
    };

    A similar source for receiving messages using the IETF-syslog protocol:

    source demo_tls_syslog_source {
        syslog(ip(0.0.0.0) port(1999)
            transport("tls")
            tls( key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                 cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert")
                 peer-verify(optional-untrusted))
        );
    };

    Caution:

    Do not forget to update the certificate and key files when they expire.

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