imptcp: Plain TCP Syslog

Provides the ability to receive syslog messages via plain TCP syslog. This is a specialised input plugin tailored for high performance on Linux. It will probably not run on any other platform. Also, it does not provide TLS services. Encryption can be provided by using stunnel.

This module has no limit on the number of listeners and sessions that can be used.

Author: Rainer Gerhards <rgerhards@adiscon.com>

Error Messages

When a message is to long it will be truncated and an error will show the remaining length of the message and the beginning of it. It will be easier to comprehend the truncation.

Configuration Directives

This plugin has config directives similar named as imtcp, but they all have PTCP in their name instead of just TCP. Note that only a subset of the parameters are supported.

Module Parameters

Note: parameter names are case-insensitive.

These parameters can be used with the “module()” statement. They apply globaly to all inputs defined by the module.

Threads <number>

Number of helper worker threads to process incoming messages. These threads are utilized to pull data off the network. On a busy system, additional helper threads (but not more than there are CPUs/Cores) can help improving performance. The default value is two, which means there is a default thread count of three (the main input thread plus two helpers). No more than 16 threads can be set (if tried to, rsyslog always resorts to 16).

processOnPoller on/off

Defaults to on

Instructs imptcp to process messages on poller thread opportunistically. This leads to lower resource footprint(as poller thread doubles up as message-processing thread too). “On” works best when imptcp is handling low ingestion rates.

At high throughput though, it causes polling delay(as poller spends time processing messages, which keeps connections in read-ready state longer than they need to be, filling socket-buffer, hence eventually applying backpressure).

It defaults to allowing messages to be processed on poller (for backward compatibility).

Input Parameters

Note: parameter names are case-insensitive.

These parameters can be used with the “input()” statement. They apply to the input they are specified with.

port <number>

Mandatory

Select a port to listen on. It is an error to specify both path and port.

path <name>

A path on the filesystem for a unix domain socket. It is an error to specify both path and port.

discardTruncatedMsg <on/off>

Default: off

When a message is split because it is to long the second part is normally processed as the next message. This can cause Problems. When this parameter is turned on the part of the message after the truncation will be discarded.

fileOwner [userName]

Default: system default

Set the file owner for the domain socket. The parameter is a user name, for which the userid is obtained by rsyslogd during startup processing. Interim changes to the user mapping are not detected.

fileOwnerNum [uid]

Default: system default

Set the file owner for the domain socket. The parameter is a numerical ID, which which is used regardless of whether the user actually exists. This can be useful if the user mapping is not available to rsyslog during startup.

fileGroup [groupName]

Default: system default

Set the group for the domain socket. The parameter is a group name, for which the groupid is obtained by rsyslogd during startup processing. Interim changes to the user mapping are not detected.

fileGroupNum [gid]

Default: system default

Set the group for the domain socket. The parameter is a numerical ID, which is used regardless of whether the group actually exists. This can be useful if the group mapping is not available to rsyslog during startup.

fileCreateMode [octalNumber]

Default: 0644

Set the access permissions for the domain socket. The value given must always be a 4-digit octal number, with the initial digit being zero. Please note that the actual permission depend on rsyslogd’s process umask. If in doubt, use “$umask 0000” right at the beginning of the configuration file to remove any restrictions.

failOnChOwnFailure [switch]

Default: on

rsyslog will not start if this is on and changing the file owner, group, or access permissions fails. Disable this to ignore these errors.

unlink on/off

Default: off

If a unix domain socket is being used this controls whether or not the socket is unlinked before listening and after closing.

name <name>

Sets a name for the inputname property. If no name is set “imptcp” is used by default. Setting a name is not strictly necessary, but can be useful to apply filtering based on which input the message was received from. Note that the name also shows up in impstats logs.

ruleset <name>

Binds specified ruleset to this input. If not set, the default ruleset is bound.

maxFrameSize <int>

Default: 200000; Max: 200000000

When in octet counted mode, the frame size is given at the beginning of the message. With this parameter the max size this frame can have is specified and when the frame gets to large the mode is switched to octet stuffing. The max value this parameter can have was specified because otherwise the integer could become negative and this would result in a Segmentation Fault.

address <name>

Default: all interfaces

On multi-homed machines, specifies to which local address the listerner should be bound.

AddtlFrameDelimiter <Delimiter>

This directive permits to specify an additional frame delimiter for plain tcp syslog. The industry-standard specifies using the LF character as frame delimiter. Some vendors, notable Juniper in their NetScreen products, use an invalid frame delimiter, in Juniper’s case the NUL character. This directive permits to specify the ASCII value of the delimiter in question. Please note that this does not guarantee that all wrong implementations can be cured with this directive. It is not even a sure fix with all versions of NetScreen, as I suggest the NUL character is the effect of a (common) coding error and thus will probably go away at some time in the future. But for the time being, the value 0 can probably be used to make rsyslog handle NetScreen’s invalid syslog/tcp framing. For additional information, see this forum thread. If this doesn’t work for you, please do not blame the rsyslog team. Instead file a bug report with Juniper!

Note that a similar, but worse, issue exists with Cisco’s IOS implementation. They do not use any framing at all. This is confirmed from Cisco’s side, but there seems to be very limited interest in fixing this issue. This directive can not fix the Cisco bug. That would require much more code changes, which I was unable to do so far. Full details can be found at the Cisco tcp syslog anomaly page.

SupportOctetCountedFraming on/off

Defaults to “on”

The legacy octed-counted framing (similar to RFC5425 framing) is activated. This is the default and should be left unchanged until you know very well what you do. It may be useful to turn it off, if you know this framing is not used and some senders emit multi-line messages into the message stream.

NotifyOnConnectionClose on/off

Defaults to off

instructs imptcp to emit a message if a remote peer closes the connection.

NotifyOnConnectionOpen on/off

Defaults to off

instructs imptcp to emit a message if a remote peer opens a connection. Hostname of the remote peer is given in the message.

KeepAlive on/off

Defaults to off

enable of disable keep-alive packets at the tcp socket layer. The default is to disable them.

KeepAlive.Probes <number>

The number of unacknowledged probes to send before considering the connection dead and notifying the application layer. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

KeepAlive.Interval <number>

The interval between subsequential keepalive probes, regardless of what the connection has exchanged in the meantime. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

KeepAlive.Time <number>

The interval between the last data packet sent (simple ACKs are not considered data) and the first keepalive probe; after the connection is marked to need keepalive, this counter is not used any further. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

RateLimit.Interval [number]

Default is 0, which turns off rate limiting

Specifies the rate-limiting interval in seconds. Set it to a number of seconds (5 recommended) to activate rate-limiting.

RateLimit.Burst [number]

Default is 10,000

Specifies the rate-limiting burst in number of messages.

compression.mode [mode]

Default is none

This is the counterpart to the compression modes set in omfwd. Please see it’s documentation for details.

flowControl <on/off>

Default: on

Flow control is used to throttle the sender if the receiver queue is near-full preserving some space for input that can not be throttled.

multiLine <on/off>

Default: off

Experimental parameter which caues rsyslog to recognise a new message only if the line feed is followed by a ‘<’ or if there are no more characters.

Statistic Counter

This plugin maintains statistics for each listener. The statistic is named “imtcp” , followed by the bound address, listener port and IP version in parenthesis. For example, the counter for a listener on port 514, bound to all interfaces and listening on IPv6 is called “imptcp(*/514/IPv6)”.

The following properties are maintained for each listener:

• submitted - total number of messages submitted for processing since startup

Caveats/Known Bugs

• module always binds to all interfaces

Example

This sets up a TCP server on port 514:

module(load="imptcp") # needs to be done just once
input(type="imptcp" port="514")

This creates a listener that listens on the local loopback interface, only.

module(load="imptcp") # needs to be done just once
input(type="imptcp" port="514" address="127.0.0.1")

Create a unix domain socket:

module(load="imptcp") # needs to be done just once
input(type="imptcp" path="/tmp/unix.sock" unlink="on")

Legacy Configuration Directives

$InputPTCPServerAddtlFrameDelimiter <Delimiter>

Equivalent to: AddTLFrameDelimiter

$InputPTCPSupportOctetCountedFraming on/off

Equivalent to: SupportOctetCountedFraming

$InputPTCPServerNotifyOnConnectionClose on/off

Equivalent to: NotifyOnConnectionClose.

$InputPTCPServerKeepAlive <on/**off**>

Equivalent to: KeepAlive

$InputPTCPServerKeepAlive_probes <number>

Equivalent to: KeepAlive.Probes

$InputPTCPServerKeepAlive_intvl <number>

Equivalent to: KeepAlive.Interval

$InputPTCPServerKeepAlive_time <number>

Equivalent to: KeepAlive.Time

$InputPTCPServerRun <port>

Equivalent to: Port

$InputPTCPServerInputName <name>

Equivalent to: Name

$InputPTCPServerBindRuleset <name>

Equivalent to: Ruleset

$InputPTCPServerHelperThreads <number>

Equivalent to: threads

$InputPTCPServerListenIP <name>

Equivalent to: Address

Caveats/Known Bugs

• module always binds to all interfaces

Example

This sets up a TCP server on port 514:

$ModLoad imptcp # needs to be done just once
$InputPTCPServerRun 514