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unix-stream, unix-dgram: Collect messages from UNIX domain sockets

1: UNIX credentials and other metadata

2: unix-stream() and unix-dgram() source options

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]);

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");
    };

1 - UNIX credentials and other metadata

Starting with AxoSyslog 3.6, the unix-stream() and unix-dgram() sources automatically extract the available UNIX credentials and other metainformation from the received log messages. The AxoSyslog application can extract the following information on Linux and FreeBSD platforms (examples show the value of the macro for the su - myuser command). Similar information is available for the systemd-journal source.

UNIX credentials available via UNIX domain sockets
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`

2 - 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:

check-hostname()


Type:	boolean (`yes` or `no`)
Default:	Use the global `check-hostname()` option, which defaults to `no`.

Checks that the hostname contains valid characters. Uses the value of the global option if not specified.

create-dirs()


Type:	yes or no
Default:	no

Description: Enable creating non-existing directories when creating files or 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, dont-store-legacy-msghdr, empty-lines, expect-hostname, kernel, no-hostname, no-multi-line, no-parse, sanitize-utf8, store-legacy-msghdr, store-raw-message, syslog-protocol, validate-utf8
Default:	empty set

Description: Specifies the log parsing options of the source.

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.
dont-store-legacy-msghdr: By default, AxoSyslog 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 (AxoSyslog 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.
empty-lines: Use the empty-lines flag to keep the empty lines of the messages. By default, AxoSyslog removes empty lines automatically.
exit-on-eof: If this flag is set on a source, AxoSyslog stops when an EOF (end of file) is received. Available in version 4.9 and later.
expect-hostname: If the expect-hostname flag is enabled, AxoSyslog 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.
guess-timezone: Attempt to guess the timezone of the message if this information is not available in the message. Works when the incoming message stream is close to real time, and the timezone information is missing from the timestamp.
kernel: The kernel flag makes the source default to the LOG_KERN | LOG_NOTICE priority if not specified otherwise.
no-header: The no-header flag triggers AxoSyslog to parse only the PRI field of incoming messages, and put the rest of the message contents into $MSG.

Its functionality is similar to that of the no-parse flag, except the no-header flag does not skip the PRI field.

Note Essentially, the no-header flag signals AxoSyslog that the syslog header is not present (or does not adhere to the conventions / RFCs), so the entire message (except from the PRI field) is put into $MSG.

Example: using the no-header flag with the syslog-parser() parser

The following example illustrates using the no-header flag with the syslog-parser() parser:
```
    parser p_syslog {
      syslog-parser(
        flags(no-header)
      );
    };
```
no-hostname: Enable the no-hostname flag if the log message does not include the hostname of the sender host. That way AxoSyslog 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.
no-parse: By default, AxoSyslog 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 AxoSyslog 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, AxoSyslog generates a new syslog header (timestamp, host, and so on) automatically. Note that even though flags(no-parse) disables message parsing, some flags can still be used, for example, the no-multi-line flag.
sanitize-utf8: When using the sanitize-utf8 flag, AxoSyslog converts non-UTF-8 input to an escaped form, which is valid UTF-8.

Prior to version 4.6, this flag worked only when parsing RFC3164 messages. Starting with version 4.6, it works also for RFC5424 and raw messages.
store-legacy-msghdr: By default, AxoSyslog stores the original incoming header of the log message, so this flag is active. To disable it, use the dont-store-legacy-msghdr flag.
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 AxoSyslog node using the syslog-ng() destination, or to a SIEM system, ensuring that the SIEM can process it. Available only in 3.16 and later.
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.
validate-utf8: The validate-utf8 flag enables encoding-verification for messages.

Prior to version 4.6, this flag worked only when parsing RFC3164 messages. Starting with version 4.6, it works also for RFC5424 and raw messages.

For RFC5424-formatted messages, if the BOM character is missing, but the message is otherwise UTF-8 compliant, AxoSyslog automatically adds the BOM character to the message.

The byte order mark (BOM) is a Unicode character used to signal the byte-order of the message text.

group()


Type:	string
Default:	root

Description: Set the gid of the socket.

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 AxoSyslog 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 AxoSyslog to execute external applications.

Using `hook-commands()` when AxoSyslog starts or stops

To execute an external program when AxoSyslog starts or stops, use the following options:

`startup()`

Type:	string
Default:	N/A

Description: Defines the external program that is executed as AxoSyslog starts.

`shutdown()`

Type:	string
Default:	N/A

Description: Defines the external program that is executed as AxoSyslog stops.

Using the hook-commands() when AxoSyslog reloads

To execute an external program when the AxoSyslog configuration is initiated or torn down, for example, on startup/shutdown or during a AxoSyslog reload, use the following options:

`setup()`

Type:	string
Default:	N/A

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

`teardown()`

Type:	string
Default:	N/A

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

Example: Using 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 AxoSyslog 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 AxoSyslog 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.

idle-timeout()


Accepted values:	number [seconds]
Default:	`0` (disabled)

Available in AxoSyslog 4.9 and later.

If set, AxoSyslog closes the client connection if no data is received for the specified amount of time (in seconds).

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 AxoSyslog 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.

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

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. Its value cannot be lower than 100, unless the dynamic-window-size() option is enabled. 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` (64 KiB).

Description: Maximum length of an incoming 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 (256 MiB).

For messages using the IETF-syslog message format (RFC5424), the maximal size of the value of an SDATA field is 64 KiB.

Note In most cases, log-msg-size() does not need to be set higher than 10 MiB.

For details on how encoding affects the size of the message, see Message size and encoding.

You can use human-readable units when setting configuration options. For details, seeNotes about the configuration syntax.

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.

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 AxoSyslog 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.

owner()


Type:	string
Default:	root

Description: Set the uid of the socket.

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. The AxoSyslog 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(), AxoSyslog 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.

Warning

When receiving messages using the UDP protocol, increase the size of the UDP receive buffer on the receiver host (that is, the AxoSyslog 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-reuseport()


Type:	yes or no
Default:	no

Description: Enables SO_REUSEPORT on systems that support it. When enabled, the kernel allows multiple UDP sockets to be bound to the same port, and the kernel load-balances incoming UDP datagrams to the sockets. The sockets are distributed based on the hash of (srcip, dstip, srcport, dstport), so the same listener should be receiving packets from the same endpoint. For example:

   source {
            network(transport("udp") so-reuseport(1) port(2000) persist-name("udp1"));
            network(so-reuseport(1) port(2000) persist-name("udp2"));
            network(so-reuseport(1) port(2000) persist-name("udp3"));
            network(so-reuseport(1) port(2000) persist-name("udp4"));
    };

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

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 version 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.