The syslog-ng() destination is a special version of the network() destination driver: by default, it sends EWMM-formatted log messages to the TCP514 port of the server.

ca-dir()

Type: Directory name
Default: none

Description: The 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 OSE clients. The syslog-ng OSE application uses the CA certificates in this directory to validate the certificate of the peer.

This option can be used together with the optional ca-file() option.

NOTE: During a TLS handshake, syslog-ng OSE automatically sets the certificate_authorities field of the certificate request based on the ca-file() and ca-dir() options.

ca-file()

Type: File name
Default: empty

Description: Optional. The name of a file that contains a set of trusted CA certificates in PEM format. The syslog-ng OSE application uses the CA certificates in this file to validate the certificate of the peer.

Example format in configuration:

ca-file("/etc/pki/tls/certs/ca-bundle.crt")

NOTE: The ca-file() option can be used together with the ca-dir() option, and it is relevant when peer-verify() is set to other than no or optional-untrusted.

NOTE: During a TLS handshake, syslog-ng OSE automatically sets the certificate_authorities field of the certificate request based on the ca-file() and ca-dir() options.

disk-buffer()

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

capacity-bytes()

Type: number (bytes)
Default: 1 MiB

Description: This is a required option. The maximum size of the disk-buffer 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.

In syslog-ng OSE version 4.2 and earlier, this option was called disk-buf-size().

compaction()

Type: yes/no
Default: no

Description: If set to yes, syslog-ng OSE prunes the unused space in the LogMessage representation, making the disk queue size smaller at the cost of some CPU time. Setting the compaction() argument to yes is recommended when numerous name-value pairs are unset during processing, or when the same names are set multiple times.

NOTE: Simply unsetting these name-value pairs by using the unset() rewrite operation is not enough, as due to performance reasons that help when syslog-ng OSE is CPU bound, the internal representation of a LogMessage will not release the memory associated with these name-value pairs. In some cases, however, the size of this overhead becomes significant (the raw message size can grow up to four times its original size), which unnecessarily increases the disk queue file size. For these cases, the compaction will drop unset values, making the LogMessage representation smaller at the cost of some CPU time required to perform compaction.

dir()

Type: string
Default: N/A

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

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

syslog-ng OSE 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 OSE will look for or create disk-buffer files in their old location. To ensure that syslog-ng OSE 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.

flow-control-window-bytes()

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. 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.

In syslog-ng OSE version 4.2 and earlier, this option was called mem-buf-size().

flow-control-window-size()

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.

In syslog-ng OSE version 4.2 and earlier, this option was called mem-buf-length().

front-cache-size()

Type: number(messages)
Default: 1000

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 already exists, the change will take effect when the disk-buffer becomes empty.

Options reliable() and capacity-bytes() are required options.

In syslog-ng OSE version 4.2 and earlier, this option was called qout-size().

prealloc()

Type: yes/no
Default: no

Description: By default, syslog-ng OSE doesn’t reserve the disk space for the disk-buffer file, since in a properly configured and sized environment the disk-buffer is practically empty, so a large preallocated disk-buffer file is just a waste of disk space. But a preallocated buffer can prevent other data from using the intended buffer space (and elicit a warning from the OS if disk space is low), preventing message loss if the buffer is actually needed. To avoid this problem, when using syslog-ng OSE 4.0 or later, you can preallocate the space for your disk-buffer files by setting prealloc(yes).

In addition to making sure that the required disk space is available when needed, preallocated disk-buffer files provide radically better (3-4x) performance as well: in case of an outage the amount of messages stored in the disk-buffer is continuously growing, and using large continuous files is faster, than constantly waiting on a file to change its size.

If you are running syslog-ng OSE on a dedicated host (always recommended for any high-volume settings), use prealloc(yes).

Available in syslog-ng OSE 4.0 and later.

reliable()

Type: yes/no
Default: no

Description: If set to yes, syslog-ng OSE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng OSE 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 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, the messages stored in the disk-buffer will be lost.

truncate-size-ratio()

Type: number((between 0 and 1))
Default: 1 (do not truncate)

Description: Limits the truncation of the disk-buffer file. Truncating the disk-buffer file can slow down the disk IO operations, but it saves disk space. By default, syslog-ng OSE version 4.0 and later doesn’t truncate disk-buffer files by default (truncate-size-ratio(1)). Earlier versions freed the disk-space when at least 10% of the disk-buffer file could be freed (truncate-size-ratio(0.1)).

syslog-ng OSE only truncates the file if the possible disk gain is more than truncate-size-ratio() times capacity-bytes().

  • Smaller values free disk space quicker.
  • Larger ratios result in better performance.

If you want to avoid performance fluctuations:

  • use truncate-size-ratio(1) (never truncate), or
  • use prealloc(yes) to reserve the entire size of the disk-buffer on disk.

CAUTION: It is not recommended to change truncate-size-ratio(). Only change its value if you understand the performance implications of doing so.

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(
                flow-control-window-bytes(10000)
                capacity-bytes(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(
                flow-control-window-size(10000)
                capacity-bytes(2000000)
                reliable(no)
                dir("/tmp/disk-buffer")
            )
        );
    };

failover()

Description: Available only in syslog-ng Open Source Edition version 3.17 and later. For details about how client-side failover works, see Client-side failover.

servers()

Type: list of IP addresses and fully-qualified domain names
Default: empty

Description: Specifies a secondary destination server where log messages are sent if the primary server becomes inaccessible. To list several failover servers, separate the address of the servers with comma. By default, syslog-ng OSE waits for the a server before switching to the next failover server is set in the time-reopen() option.
If failback() is not set, syslog-ng OSE does not attempt to return to the primary server even if it becomes available. In case the failover server fails, syslog-ng OSE attempts to connect the next failover server in the list in round-robin fashion.

CAUTION: The failover servers must be accessible on the same port as the primary server.

failback()

Description: Available only in syslog-ng Open Source Edition version 3.17 and later.

When syslog-ng OSE starts up, it always connects to the primary server first. In the failover() option there is a possibility to customize the failover modes.
Depending on how you set the failback() option, syslog-ng OSE behaves as follows:

  • round-robin mode: If failback() is not set, syslog-ng OSE does not attempt to return to the primary server even if it becomes available. In case the failover server fails, syslog-ng OSE attempts to connect the next failover server in the list in round-robin fashion.

    Example: round-robin mode

    In the following example syslog-ng OSE handles the logservers in round-robin fashion if the primary logserver becomes inaccessible (therefore failback() option is not set).

      destination d_network {                                      
      network(                                                
          "primary-server.com"                               
          port(601)                                          

      failover( servers("failover-server1", "failover-server2") ) 
      );                                                           
  };

  • failback mode: If failback() is set, syslog-ng OSE attempts to return to the primary server.

    After syslog-ng OSE connects a secondary server during a failover, it sends a probe every tcp-probe-interval() seconds towards the primary server. If the primary logserver responds with a TCP ACK packet, the probe is successful. When the number of successful probes reaches the value set in the successful-probes-required() option, syslog-ng OSE tries to connect the primary server using the last probe.

    NOTE: syslog-ng OSE always waits for the result of the last probe before sending the next message. So if one connection attempt takes longer than the configured interval, that is, it waits for connection time out, you may experience longer intervals between actual probes.

    Example: failback mode

    In the following example syslog-ng OSE attempts to return to the primary logserver, as set in the failback() option: it will check if the server is accessible every tcp-probe-interval() seconds, and reconnect to the primary logserver after three successful connection attempts.

      destination d_network_2 {
          network(                                                
              "primary-server.com"                               
              port(601)                                          
              failover(                                          
                                                                    
                  servers("failover-server1", "failover-server2") 
                  failback(                                     
                      successful-probes-required()             
                      tcp-probe-interval()                     
                  )                                             
              )                                                  
  );                                                           
  };

Default value for tcp-probe-interval(): 60 seconds

Default value for successful-probes-required(): 3

NOTE: This option is not available for the connection-less UDP protocol, because in this case the client does not detect that the destination becomes inaccessible.

Example: Specifying failover servers for syslog() destinations

The following example specifies two failover servers for a simple syslog() destination.

destination d_syslog_tcp{
    syslog("10.100.20.40"
        transport("tcp")
        port(6514)
        failover-servers("10.2.3.4", "myfailoverserver")
    );
};

The following example specifies a failover server for a network() destination that uses TLS encryption.

destination d_syslog_tls{
    network("10.100.20.40"
        transport("tls")
        port(6514)
        failover-servers("10.2.3.4", "myfailoverserver")
        tls(peer-verify(required-trusted)
        ca-dir('/opt/syslog-ng/etc/syslog-ng/keys/ca.d/')
        key-file('/opt/syslog-ng/etc/syslog-ng/keys/client_key.pem')
        cert-file('/opt/syslog-ng/etc/syslog-ng/keys/client_certificate.pem'))
    );
};

flags()

Type: no-multi-line, syslog-protocol
Default: empty set

Description: Flags influence the behavior of the destination driver.

  • no-multi-line: The no-multi-line flag disables line-breaking in the messages: the entire message is converted to a single line.

  • syslog-protocol: The syslog-protocol flag instructs the driver to format the messages according to the new IETF syslog protocol standard (RFC-5424), but without the frame header. If this flag is enabled, macros used for the message have effect only for the text of the message, the message header is formatted to the new standard. Note that this flag is not needed for the syslog driver, and that the syslog driver automatically adds the frame header to the messages.

flush-lines()

Type: number
Default: Use global setting (exception: for http() destination, the default is 1).

Description: Specifies how many lines are flushed to a destination at a time. The syslog-ng OSE 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.

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

For optimal performance when sending messages to an syslog-ng OSE server, make sure that the value of flush-lines() is smaller than the window size set in the log-iw-size() option in the source of your server.

frac-digits()

Type: number
Default: 0

Description: The syslog-ng OSE 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: The syslog-ng OSE application can add the fractions to non-ISO8601 timestamps as well.

NOTE: As syslog-ng OSE is precise up to the microsecond, when the frac-digits() option is set to a value higher than 6, syslog-ng OSE will truncate the fraction seconds in the timestamps after 6 digits.

ip-protocol()

Type: number
Default: 4

Description: Determines the internet protocol version of the given driver (network() or syslog()). The possible values are 4 and 6, corresponding to IPv4 and IPv6. The default value is ip-protocol(4).

Note that listening on a port using IPv6 automatically means that you are also listening on that port using IPv4. That is, if you want to have receive messages on an IP-address/port pair using both IPv4 and IPv6, create a source that uses the ip-protocol(6). You cannot have two sources with the same IP-address/port pair, but with different ip-protocol() settings (it causes an Address already in use error).

For example, the following source receives messages on TCP, using the network() driver, on every available interface of the host on both IPv4 and IPv6.

source s_network_tcp { network( transport("tcp") ip("::") ip-protocol(6) port(601) ); };

ip-tos()

Type: number
Default: 0

Description: Specifies the Type-of-Service value of outgoing packets.

ip-ttl()

Type: number
Default: 0

Description: Specifies the Time-To-Live value of outgoing packets.

keep-alive()

Type: yes or no
Default: yes

Description: Specifies whether connections to sources should be closed when syslog-ng OSE is forced to reload its configuration (upon the receipt of a SIGHUP signal). Note that this applies to the server (source) side of the syslog-ng OSE connections, client-side (destination) connections are always reopened after receiving a HUP signal unless the keep-alive option is enabled for the destination.

localip()

Type: string
Default: 0.0.0.0

Description: The IP address to bind to before connecting to target.

localport()

Type: number
Default: 0

Description: The port number to bind to. Messages are sent from this port.

log-fifo-size()

Type: number
Default: Use global setting.

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

mark-freq()

Accepted values: number [seconds]
Default: 1200

Description: An alias for the obsolete mark() option, retained for compatibility with syslog-ng OSE 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.

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 OSE 3.4 and later.

port() or destport()

Type: number
Default: 601

Description: The port number to connect to. Note that the default port numbers used by syslog-ng OSE do not comply with the latest RFC which was published after the release of syslog-ng OSE 3.0.2, therefore the default port numbers will change in the future releases.

server()

Type: hostname or IP address
Default: 127.0.0.1

Description: The hostname or IP address of the syslog-ng OSE server.

so-broadcast()

Type: yes or no
Default: no

Description: This option controls the SO_BROADCAST socket option required to make syslog-ng OSE send messages to a broadcast address. For details, see the socket(7) manual page.

so-keepalive()

Type: yes or no
Default: no

Description: Enables keep-alive messages, keeping the socket open. This only effects TCP and UNIX-stream sockets. For details, see the socket(7) manual page.

so-rcvbuf()

Type: number
Default: 0

Description: Specifies the size of the socket receive buffer in bytes. For details, see the socket(7) manual page.

CAUTION: When receiving messages using the UDP protocol, increase the size of the UDP receive buffer on the receiver host
(that is, the syslog-ng OSE server or relay receiving the messages).

Note that on certain platforms, for example, on Red Hat Enterprise Linux 5, even low message load (~200 messages per second) can result in message loss, unless the so-rcvbuf() option of the source is increased. In this cases, you will need to increase the net.core.rmem_max parameter of the host (for example, to 1024000), but do not modify net.core.rmem_default parameter.

As a general rule, increase the so-rcvbuf() so that the buffer size in kilobytes is higher than the rate of incoming messages per second.
For example, to receive 2000 messages per second, set the so-rcvbuf() at least to 2 097 152 bytes.

so-sndbuf()

Type: number
Default: 0

Description: Specifies the size of the socket send buffer in bytes. For details, see the socket(7) manual page.

spoof-source()

Type: yes or no
Default: no

Description: Enables source address spoofing. This means that the host running syslog-ng OSE generates UDP packets with the source IP address matching the original sender of the message. It is useful when you want to perform some kind of preprocessing using syslog-ng OSE then forward messages to your central log management solution with the source address of the original sender. This option only works for UDP destinations though the original message can be received by TCP as well. This option is only available if syslog-ng OSE was compiled using the –enable-spoof-source configuration option.

The maximum size of spoofed datagrams in udp() destinations is set to 1024 bytes by default. To change the maximum size, use the spoof-source-max-msglen() option.

NOTE: Anything above the size of the maximum transmission unit (MTU), which is 1500 bytes by default, is not recommended because of fragmentation.

The maximum datagram in IP protocols (both IPv4 and IPv6) is 65535 bytes including the IP and UDP headers. The minimum size of the IPv4 header is 20 bytes, the IPv6 is 40 bytes, and the UDP is 8 bytes.

suppress()

Type: seconds
Default: 0 (disabled)

Description: If several identical log messages would be sent to the destination without any other messages between the identical messages (for example, an application repeated an error message ten times), syslog-ng OSE can suppress the repeated messages and send the message only once, followed by the Last message repeated n times. message. The parameter of this option specifies the number of seconds syslog-ng OSE waits for identical messages.

tcp-keepalive-intvl()

Type: number [seconds]
Default: 10

Description: Specifies the interval (number of seconds) between subsequential keepalive probes, regardless of the traffic exchanged in the connection. This option is equivalent to /proc/sys/net/ipv4/tcp_keepalive_intvl.

CAUTION: The tcp-keepalive-time(), tcp-keepalive-probes(), and tcp-keepalive-intvl() options only work on platforms which support the TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL setsockopts. Currently, this is Linux. A connection that has no traffic is closed after tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes() seconds.

Available in syslog-ng OSE version 3.4 and later.

CAUTION: Prior to syslog-ng OSE 3.29, syslog-ng OSE uses the kernel default values for the following socket options: TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL (Only applies to systems, where those options are supported.) Unfortunately those default values are not optimal for a typical logging application. You can return to the old behavior by setting those values to zero “0”.

tcp-keepalive-probes()

Type: number
Default: 6

Description: Specifies the number of unacknowledged probes to send before considering the connection dead. This option is equivalent to /proc/sys/net/ipv4/tcp_keepalive_probes.

CAUTION: The tcp-keepalive-time(), tcp-keepalive-probes(), and tcp-keepalive-intvl() options only work on platforms which support the TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL setsockopts. Currently, this is Linux. A connection that has no traffic is closed after tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes() seconds.

Available in syslog-ng OSE version 3.4 and later.

CAUTION: Prior to syslog-ng OSE 3.29, syslog-ng OSE uses the kernel default values for the following socket options: TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL (Only applies to systems, where those options are supported.) Unfortunately those default values are not optimal for a typical logging application. You can return to the old behavior by setting those values to zero “0”.

tcp-keepalive-time()

Type: number [seconds]
Default: 60

Description: Specifies the interval (in seconds) between the last data packet sent and the first keepalive probe. This option is equivalent to /proc/sys/net/ipv4/tcp_keepalive_time.

CAUTION: The tcp-keepalive-time(), tcp-keepalive-probes(), and tcp-keepalive-intvl() options only work on platforms which support the TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL setsockopts. Currently, this is Linux. A connection that has no traffic is closed after tcp-keepalive-time() + tcp-keepalive-intvl() * tcp-keepalive-probes() seconds.

Available in syslog-ng OSE version 3.4 and later.

CAUTION: Prior to syslog-ng OSE 3.29, syslog-ng OSE uses the kernel default values for the following socket options: TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL (Only applies to systems, where those options are supported.) Unfortunately those default values are not optimal for a typical logging application. You can return to the old behavior by setting those values to zero “0”.

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 OSE. 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 OSE itself). For network destinations make sure the receiver can cope with the custom format defined.

template-escape()

Type: yes or no
Default: no

Description: Turns on escaping for the ', ", and backspace characters in templated output files. This is useful for generating SQL statements and quoting string contents so that parts of the log message are not interpreted as commands to the SQL server.

NOTE: In syslog-ng OSE 4.5 and later versions template-escape(yes) escapes the top-level template function in case of nested template functions.

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 disk-buffer as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

time-zone()

Type: name of the timezone, or the timezone offset
Default:  

Description: The default timezone for messages read from the source. Applies only if no timezone is specified within the message itself.

The timezone can be specified by using the name, 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.

tls()

Type: tls options
Default: n/a

Description: This option sets various options related to TLS encryption, for example, key/certificate files and trusted CA locations. TLS can be used only with tcp-based transport protocols. For details, see TLS options.

transport()

Type: udp, tcp, or tls
Default: tcp

Description: Specifies the protocol used to send messages to the destination server.

If you use the udp transport, syslog-ng OSE automatically sends multicast packets if a multicast destination address is specified. The tcp transport does not support multicasting.

ts-format()

Type: rfc3164, bsd, rfc3339, iso
Default: rfc3164

Description: Override the global timestamp format (set in the global ts-format() parameter) for the specific destination. For details, see ts-format().

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.

Updated: