unix-stream, unix-dgram: Collecting messages from UNIX domain sockets
The unix-stream() and unix-dgram() drivers open an AF_UNIX socket and start listening on it for messages. The unix-stream() driver is primarily used on Linux and uses SOCK_STREAM semantics (connection oriented, no messages are lost), while unix-dgram() is used on BSDs and uses SOCK_DGRAM semantics: this may result in lost local messages if the system is overloaded.
To avoid denial of service attacks when using connection-oriented protocols, the number of simultaneously accepted connections should be limited. This can be achieved using the max-connections() parameter. The default value of this parameter is quite strict, you might have to increase it on a busy system.
Both unix-stream and unix-dgram have a single required argument that specifies the filename of the socket to create. For the list of available optional parameters, see unix-stream() and unix-dgram() source options
Declaration:
unix-stream(filename [options]); unix-dgram(filename [options]);
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NOTE:
syslogd on Linux originally used SOCK_STREAM sockets, but some distributions switched to SOCK_DGRAM around 1999 to fix a possible DoS problem. On Linux you can choose to use whichever driver you like as syslog clients automatically detect the socket type being used. |
Example: Using the unix-stream() and unix-dgram() drivers
source s_stream {
unix-stream("/dev/log" max-connections(10));
};source s_dgram {
unix-dgram("/var/run/log");
};UNIX credentials and other metadata
Starting with syslog-ng OSE
| Macro | Description |
|---|---|
| ${.unix.cmdline} | The name (without the path) and command-line options of the executable belonging to the PID that sent the message. For example, su - myuser |
| ${.unix.exe} | The path of the executable belonging to the PID that sent the message. For example, /usr/bin/su |
| ${.unix.gid} | The group ID (GID) corresponding to the UID of the application that sent the log message. Note that this is the ID number of the group, not its human-readable name. For example, 0 |
| ${.unix.pid} |
The process ID (PID) of the application that sent the log message. For example, 774. Note that on every UNIX platforms, if the system() source uses sockets, it will overwrite the PID macro with the value of ${.unix.pid}, if it is available. |
| ${.unix.uid} | The user ID (UID) of the application that sent the log message. Note that this is the ID number of the user, not its human-readable name. For example, 0 |
unix-stream() and unix-dgram() source options
These two drivers behave similarly: they open an AF_UNIX socket and start listening on it for messages. The following options can be specified for these drivers:
create-dirs()
| Type: | yes or no |
| Default: | no |
Description: Enable creating non-existing directories when creating the socket files.
encoding()
| Type: | string |
| Default: |
Description: Specifies the character set (encoding, for example UTF-8) of messages using the legacy BSD-syslog protocol. To list the available character sets on a host, execute the iconv -l command. For details on how encoding affects the size of the message, see Message size and encoding.
flags()
| Type: | assume-utf8, empty-lines, expect-hostname, kernel, no-hostname, no-multi-line, no-parse, sanitize-utf8, store-legacy-msghdr, syslog-protocol, validate-utf8 |
| Default: | empty set |
Description: Specifies the log parsing options of the source.
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assume-utf8: The assume-utf8 flag assumes that the incoming messages are UTF-8 encoded, but does not verify the encoding. If you explicitly want to validate the UTF-8 encoding of the incoming message, use the validate-utf8 flag.
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empty-lines: Use the empty-lines flag to keep the empty lines of the messages. By default, syslog-ng OSE removes empty lines automatically.
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expect-hostname: If the expect-hostname flag is enabled, syslog-ng OSE will assume that the log message contains a hostname and parse the message accordingly. This is the default behavior for TCP sources. Note that pipe sources use the no-hostname flag by default.
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kernel: The kernel flag makes the source default to the LOG_KERN | LOG_NOTICE priority if not specified otherwise.
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no-hostname: Enable the no-hostname flag if the log message does not include the hostname of the sender host. That way, syslog-ng OSE assumes that the first part of the message header is ${PROGRAM} instead of ${HOST}. For example:
source s_dell { network(port(2000) flags(no-hostname)); }; -
no-multi-line: The no-multi-line flag disables line-breaking in the messages: the entire message is converted to a single line. Note that this happens only if the underlying transport method actually supports multi-line messages. Currently the file() and pipe() drivers support multi-line messages.
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no-parse: By default, syslog-ng OSE parses incoming messages as syslog messages. The no-parse flag completely disables syslog message parsing and processes the complete line as the message part of a syslog message. The syslog-ng OSE application will generate a new syslog header (timestamp, host, and so on) automatically and put the entire incoming message into the MESSAGE part of the syslog message (available using the ${MESSAGE} macro). This flag is useful for parsing messages not complying to the syslog format.
If you are using the flags(no-parse) option, then syslog message parsing is completely disabled, and the entire incoming message is treated as the ${MESSAGE} part of a syslog message. In this case, syslog-ng OSE generates a new syslog header (timestamp, host, and so on) automatically. Note that since flags(no-parse) disables message parsing, it interferes with other flags, for example, disables flags(no-multi-line).
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dont-store-legacy-msghdr: By default, syslog-ng stores the original incoming header of the log message. This is useful if the original format of a non-syslog-compliant message must be retained (syslog-ng automatically corrects minor header errors, for example, adds a whitespace before msg in the following message: Jan 22 10:06:11 host program:msg). If you do not want to store the original header of the message, enable the dont-store-legacy-msghdr flag.
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sanitize-utf8: When using the sanitize-utf8 flag, syslog-ng OSE converts non-UTF-8 input to an escaped form, which is valid UTF-8.
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store-raw-message: Save the original message as received from the client in the ${RAWMSG} macro. You can forward this raw message in its original form to another syslog-ng node using the syslog-ng() destination, or to a SIEM system, ensuring that the SIEM can process it. Available only in
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syslog-protocol: The syslog-protocol flag specifies that incoming messages are expected to be formatted according to the new IETF syslog protocol standard (RFC5424), but without the frame header. Note that this flag is not needed for the syslog driver, which handles only messages that have a frame header.
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validate-utf8: The validate-utf8 flag enables encoding-verification for messages formatted according to the new IETF syslog standard (for details, see IETF-syslog messages). If the
BOM 1character is missing, but the message is otherwise UTF-8 compliant, syslog-ng automatically adds the BOM character to the message.
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.
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NOTE: The syslog-ng OSE 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 OSE to execute external applications. |
Using the hook-commands() when syslog-ng OSE starts or stops
To execute an external program when syslog-ng OSE starts or stops, use the following options:
| startup() | |
| Type: | string |
| Default: | N/A |
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Description: Defines the external program that is executed as syslog-ng OSE starts. | |
| shutdown() | |
| Type: | string |
| Default: | N/A |
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Description: Defines the external program that is executed as syslog-ng OSE stops. | |
Using the hook-commands() when syslog-ng OSE reloads
To execute an external program when the syslog-ng OSE configuration is initiated or torn down, for example, on startup/shutdown or during a syslog-ng OSE reload, use the following options:
| setup() | |
| Type: | string |
| Default: | N/A |
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Description: Defines an external program that is executed when the syslog-ng OSE configuration is initiated, for example, on startup or during a syslog-ng OSE reload. | |
| teardown() | |
| Type: | string |
| Default: | N/A |
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Description: Defines an external program that is executed when the syslog-ng OSE configuration is stopped or torn down, for example, on shutdown or during a syslog-ng OSE 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 as syslog-ng OSE 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 OSE 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")
)
);
};host-override()
| Type: | string |
| Default: |
Description: Replaces the ${HOST} part of the message with the parameter string.
keep-alive()
| Type: | yes or no |
| Default: | yes |
Description: Selects whether to keep connections open when syslog-ng is restarted, cannot be used with unix-dgram().
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.
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Caution:
To use the S_ macros, the keep-timestamp() option must be enabled (this is the default behavior of syslog-ng OSE). |
listen-backlog()
| Type: | integer |
| Default: | 256 |
Description: Available only for stream based transports (unix-stream, tcp, tls). In TCP, connections are treated incomplete until the three-way handshake is completed between the server and the client. Incomplete connection requests wait on the TCP port for the listener to accept the request. The listen-backlog() option sets the maximum number of incomplete connection requests. For example:
source s_network {
network(
ip("192.168.1.1")
transport("tcp")
listen-backlog(2048)
);
};
log-fetch-limit()
| Type: | number |
| Default: | 100 |
Description: The maximum number of messages fetched from a source during a single poll loop. The destination queues might fill up before flow-control could stop reading if log-fetch-limit() is too high.
log-iw-size()
| Type: | number |
| Default: | 100 |
Description: The size of the initial window, this value is used during flow control. For details on flow control, see Managing incoming and outgoing messages with flow-control.
log-msg-size()
| Type: | number (bytes) |
| Default: | Use the global log-msg-size() option, which defaults to 65536. |
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.
In most cases, it is not recommended to set log-msg-size() higher than 10 MiB.
For details on how encoding affects the size of the message, see Message size and encoding.
Uses the value of the global option if not specified.
log-prefix() (DEPRECATED)
| Type: | string |
| Default: |
Description: A string added to the beginning of every log message. It can be used to add an arbitrary string to any log source, though it is most commonly used for adding kernel: to the kernel messages on Linux.
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NOTE:
This option is deprecated. Use program-override() instead. |
max-connections()
| Type: | number (simultaneous connections) |
| Default: | 256 |
Description: Limits the number of simultaneously open connections. Cannot be used with unix-dgram().
optional()
| Type: | yes or no |
| Default: |
Description: Instruct syslog-ng to ignore the error if a specific source cannot be initialized. No other attempts to initialize the source will be made until the configuration is reloaded. This option currently applies to the pipe(), unix-dgram, and unix-stream drivers.
pad-size()
| Type: | number |
| Default: | 0 |
Description: Specifies input padding. Some operating systems (such as HP-UX) pad all messages to block boundary. This option can be used to specify the block size. (HP-UX uses 2048 bytes). The syslog-ng OSE application will pad reads from the associated device to the number of bytes set in pad-size(). Mostly used on HP-UX where /dev/log is a named pipe and every write is padded to 2048 bytes. If pad-size() was given and the incoming message does not fit into pad-size(), syslog-ng will not read anymore from this pipe and displays the following error message:
Padding was set, and couldn't read enough bytes
perm()
| Type: | number (octal notation) |
| Default: | 0666 |
Description: Set the permission mask. For octal numbers prefix the number with '0', for example: use 0755 for rwxr-xr-x.
program-override()
| Type: | string |
| Default: |
Description: Replaces the ${PROGRAM} part of the message with the parameter string. For example, to mark every message coming from the kernel, include the program-override("kernel") option in the source containing /proc/kmsg.
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.
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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 such 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. |
tags()
| Type: | string |
| Default: |
Description: Label the messages received from the source with custom tags. Tags must be unique, and enclosed between double quotes. When adding multiple tags, separate them with comma, for example tags("dmz", "router"). This option is available only in syslog-ng 3.1 and later.
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.
stdin: Collecting messages from the standard input stream
The stdin() driver collects messages from the standard input stream. When the standard input stream is closed, syslog-ng stops and stdin() inherits all options from the file() source, including multi-line options, or flags(no-parse).
The stdin() driver causes syslog-ng to exit once it hits end-of-file (EOF).
Declaration:
stdin();
Example: Using the stdin() driver
@version: 3.18
log {
source { stdin(); };
destination { file("/dev/stdout"); };
};
The following code snippet is an example of how the stdin() driver is used to collect a test message:
$ echo "this is a test message" | ./syslog-ng -Fe --no-caps [2017-11-14T13:47:16.757938] syslog-ng starting up; version='3.12.1' [2017-11-14T13:47:16.758195] syslog-ng shutting down; version='3.12.1' Nov 14 13:47:16 testserver this is a test message