imuxsock: Unix Socket Input Module
Module Name: | imuxsock |
Author: |
Purpose
This module provides the ability to accept syslog messages from applications running on the local system via Unix sockets. Most importantly, this is the mechanism by which the syslog(3) call delivers syslog messages to rsyslogd.
Notable Features
Configuration Parameters
Note
Parameter names are case-insensitive.
Module Parameters
Warning
When running under systemd, many “sysSock.” parameters are ignored. See parameter descriptions and the Coexistence with systemd section for details.
SysSock.IgnoreTimestamp
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
Ignore timestamps included in the messages, applies to messages received via the system log socket.
SysSock.IgnoreOwnMessages
type | default | mandatory |
|
|---|---|---|---|
binary | on | no | none |
Ignores messages that originated from the same instance of rsyslogd. There usually is no reason to receive messages from ourselves. This setting is vital when writing messages to the systemd journal.
New in version 7.3.7.
See also
See omjournal module documentation for a more in-depth description.
SysSock.Use
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
Listen on the default local log socket (/dev/log) or, if provided, use
the log socket value assigned to the SysSock.Name parameter instead
of the default. This is most useful if you run multiple instances of
rsyslogd where only one shall handle the system log socket. Unless
disabled by the SysSock.Unlink setting, this socket is created
upon rsyslog startup and deleted upon shutdown, according to
traditional syslogd behavior.
The behavior of this parameter is different for systemd systems. For those
systems, SysSock.Use still needs to be enabled, but the value of SysSock.Name is ignored and the socket provided by systemd is used
instead. If this parameter is not enabled, then imuxsock will only be
of use if a custom input is configured.
See the Coexistence with systemd section for details.
SysSock.Name
type | default | mandatory |
|
|---|---|---|---|
word | /dev/log | no |
|
Specifies an alternate log socket to be used instead of the default system
log socket, traditionally /dev/log. Unless disabled by the SysSock.Unlink setting, this socket is created upon rsyslog startup
and deleted upon shutdown, according to traditional syslogd behavior.
- The behavior of this parameter is different for systemd systems. See the
Coexistence with systemd section for details.
SysSock.FlowControl
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Specifies if flow control should be applied to the system log socket.
SysSock.UsePIDFromSystem
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Specifies if the pid being logged shall be obtained from the log socket itself. If so, the TAG part of the message is rewritten. It is recommended to turn this option on, but the default is “off” to keep compatible with earlier versions of rsyslog.
New in version 5.7.0.
SysSock.RateLimit.Interval
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 0 | no |
|
Specifies the rate-limiting interval in seconds. Default value is 0, which turns off rate limiting. Set it to a number of seconds (5 recommended) to activate rate-limiting. The default of 0 has been chosen as people experienced problems with this feature activated by default. Now it needs an explicit opt-in by setting this parameter.
SysSock.RateLimit.Burst
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 200 | (2^31)-1 | no |
|
Specifies the rate-limiting burst in number of messages.
New in version 5.7.1.
SysSock.RateLimit.Severity
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 1 | no |
|
Specifies the severity of messages that shall be rate-limited.
SysSock.UseSysTimeStamp
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
The same as the input parameter UseSysTimeStamp, but for the system log
socket. This parameter instructs imuxsock to obtain message time from
the system (via control messages) instead of using time recorded inside
the message. This may be most useful in combination with systemd. Due to
the usefulness of this functionality, we decided to enable it by default.
As such, the behavior is slightly different than previous versions.
However, we do not see how this could negatively affect existing environments.
New in version 5.9.1.
SysSock.Annotate
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Turn on annotation/trusted properties for the system log socket. See the Trusted (syslog) properties section for more info.
SysSock.ParseTrusted
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
If SysSock.Annotation is turned on, create JSON/lumberjack properties
out of the trusted properties (which can be accessed via advanced JSON Variables, e.g. $!pid) instead of adding them to the message.
New in version 7.2.7: advanced directive introduced
New in version 7.3.8: advanced directive introduced
New in version 6.5.0: obsolete legacy directive introduced
SysSock.Unlink
type | default | mandatory |
|
|---|---|---|---|
binary | on | no | none |
If turned on (default), the system socket is unlinked and re-created when opened and also unlinked when finally closed. Note that this setting has no effect when running under systemd control (because systemd handles the socket. See the Coexistence with systemd section for details.
New in version 7.3.9.
SysSock.UseSpecialParser
type | default | mandatory |
|
|---|---|---|---|
binary | on | no | none |
The equivalent of the UseSpecialParser input parameter, but
for the system socket. If turned on (the default) a special parser is
used that parses the format that is usually used
on the system log socket (the one syslog(3) creates). If set to
“off”, the regular parser chain is used, in which case the format on the
log socket can be arbitrary.
Note
When the special parser is used, rsyslog is able to inject a more precise timestamp into the message (it is obtained from the log socket). If the regular parser chain is used, this is not possible.
New in version 8.9.0: The setting was previously hard-coded “on”
SysSock.ParseHostname
type | default | mandatory |
|
|---|---|---|---|
binary | off | no | none |
Note
This option only has an effect if SysSock.UseSpecialParser is
set to “off”.
Normally, the local log sockets do not contain hostnames. If set to on, parsers will expect hostnames just like in regular formats. If set to off (the default), the parser chain is instructed to not expect them.
New in version 8.9.0.
Input Parameters
Ruleset
type | default | mandatory |
|
|---|---|---|---|
string | default ruleset | no | none |
Binds specified ruleset to this input. If not set, the default ruleset is bound.
New in version 8.17.0.
IgnoreTimestamp
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
Ignore timestamps included in messages received from the input being defined.
IgnoreOwnMessages
type | default | mandatory |
|
|---|---|---|---|
binary | on | no | none |
Ignore messages that originated from the same instance of rsyslogd. There usually is no reason to receive messages from ourselves. This setting is vital when writing messages to the systemd journal.
New in version 7.3.7.
See also
See omjournal module documentation for a more in-depth description.
FlowControl
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Specifies if flow control should be applied to the input being defined.
RateLimit.Interval
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 0 | no |
|
Specifies the rate-limiting interval in seconds. Default value is 0, which turns off rate limiting. Set it to a number of seconds (5 recommended) to activate rate-limiting. The default of 0 has been chosen as people experienced problems with this feature activated by default. Now it needs an explicit opt-in by setting this parameter.
RateLimit.Burst
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 200 | (2^31)-1 | no |
|
Specifies the rate-limiting burst in number of messages.
New in version 5.7.1.
RateLimit.Severity
type | default | max | mandatory |
|
|---|---|---|---|---|
integer | 1 | no |
|
Specifies the severity of messages that shall be rate-limited.
UsePIDFromSystem
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Specifies if the pid being logged shall be obtained from the log socket itself. If so, the TAG part of the message is rewritten. It is recommended to turn this option on, but the default is “off” to keep compatible with earlier versions of rsyslog.
UseSysTimeStamp
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
This parameter instructs imuxsock to obtain message time from
the system (via control messages) instead of using time recorded inside
the message. This may be most useful in combination with systemd. Due to
the usefulness of this functionality, we decided to enable it by default.
As such, the behavior is slightly different than previous versions.
However, we do not see how this could negatively affect existing environments.
New in version 5.9.1.
CreatePath
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Create directories in the socket path if they do not already exist. They are created with 0755 permissions with the owner being the process under which rsyslogd runs. The default is not to create directories. Keep in mind, though, that rsyslogd always creates the socket itself if it does not exist (just not the directories by default).
This option is primarily considered useful for defining additional sockets that reside on non-permanent file systems. As rsyslogd probably starts up before the daemons that create these sockets, it is a vehicle to enable rsyslogd to listen to those sockets even though their directories do not yet exist.
New in version 4.7.0.
New in version 5.3.0.
Socket
type | default | mandatory |
|
|---|---|---|---|
string | none | no |
|
Adds additional unix socket. Formerly specified with the -a option.
HostName
type | default | mandatory |
|
|---|---|---|---|
string | NULL | no |
|
Allows overriding the hostname that shall be used inside messages taken from the input that is being defined.
Annotate
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Turn on annotation/trusted properties for the input that is being defined. See the Trusted (syslog) properties section for more info.
ParseTrusted
type | default | mandatory |
|
|---|---|---|---|
binary | off | no |
|
Equivalent to the SysSock.ParseTrusted module parameter, but applies
to the input that is being defined.
Unlink
type | default | mandatory |
|
|---|---|---|---|
binary | on | no |
|
If turned on (default), the socket is unlinked and re-created when opened and also unlinked when finally closed. Set it to off if you handle socket creation yourself.
Note
Note that handling socket creation oneself has the advantage that a limited amount of messages may be queued by the OS if rsyslog is not running.
New in version 7.3.9.
UseSpecialParser
type | default | mandatory |
|
|---|---|---|---|
binary | on | no | none |
Equivalent to the SysSock.UseSpecialParser module parameter, but applies
to the input that is being defined.
New in version 8.9.0: The setting was previously hard-coded “on”
ParseHostname
type | default | mandatory |
|
|---|---|---|---|
binary | off | no | none |
Equivalent to the SysSock.ParseHostname module parameter, but applies
to the input that is being defined.
New in version 8.9.0.
Input rate limiting
rsyslog supports (optional) input rate limiting to guard against the problems
of a wild running logging process. If more than SysSock.RateLimit.Interval * SysSock.RateLimit.Burst log messages
are emitted from the same process, those messages with SysSock.RateLimit.Severity or lower will be dropped. It is not possible
to recover anything about these messages, but imuxsock will tell you how
many it has dropped once the interval has expired AND the next message is
logged. Rate-limiting depends on SCM\_CREDENTIALS. If the platform does
not support this socket option, rate limiting is turned off. If multiple
sockets are configured, rate limiting works independently on each of
them (that should be what you usually expect).
The same functionality is available for additional log sockets, in which case the config statements just use the prefix RateLimit… but otherwise works exactly the same. When working with severities, please keep in mind that higher severity numbers mean lower severity and configure things accordingly. To turn off rate limiting, set the interval to zero.
New in version 5.7.1.
Trusted (syslog) properties
rsyslog can annotate messages from system log sockets (via imuxsock) with so-called Trusted syslog properties, (or just “Trusted Properties” for short). These are message properties not provided by the logging client application itself, but rather obtained from the system. As such, they can not be faked by the user application and are trusted in this sense. This feature is based on a similar idea introduced in systemd.
This feature requires a recent enough Linux Kernel and access to
the /proc file system. In other words, this may not work on all
platforms and may not work fully when privileges are dropped (depending
on how they are dropped). Note that trusted properties can be very
useful, but also typically cause the message to grow rather large. Also,
the format of log messages is changed by adding the trusted properties at
the end. For these reasons, the feature is not enabled by default.
If you want to use it, you must turn it on (via SysSock.Annotate and Annotate).
New in version 5.9.4.
See also
Flow-control of Unix log sockets
If processing queues fill up, the unix socket reader is blocked for a short while to help prevent overrunning the queues. If the queues are overrun, this may cause excessive disk-io and impact performance.
While turning on flow control for many systems does not hurt, it can lead to a very unresponsive system and as such is disabled by default.
This means that log records are placed as quickly as possible into the
processing queues. If you would like to have flow control, you
need to enable it via the SysSock.FlowControl and FlowControl config
directives. Just make sure you have thought about the implications and have
tested the change on a non-production system first.
Control over application timestamps
Application timestamps are ignored by default. This is needed, as some
programs (e.g. sshd) log with inconsistent timezone information, what
messes up the local logs (which by default don’t even contain time zone
information). This seems to be consistent with what sysklogd has done for
many years. Alternate behaviour may be desirable if gateway-like processes
send messages via the local log slot. In that case, it can be enabled via
the SysSock.IgnoreTimestamp and IgnoreTimestamp config directives.
Coexistence with systemd
Rsyslog should by default be configured for systemd support on all platforms that usually run systemd (which means most Linux distributions, but not, for example, Solaris).
Rsyslog is able to coexist with systemd with minimal changes on the part of the
local system administrator. While the systemd journal now assumes full
control of the local /dev/log system log socket, systemd provides
access to logging data via the /run/systemd/journal/syslog log socket.
This log socket is provided by the syslog.socket file that is shipped
with systemd.
The imuxsock module can still be used in this setup and provides superior performance over imjournal, the alternative journal input module.
Note
It must be noted, however, that the journal tends to drop messages when it becomes busy instead of forwarding them to the system log socket. This is because the journal uses an async log socket interface for forwarding instead of the traditional synchronous one.
New in version 8.32.0: rsyslog emits an informational message noting the system log socket provided by systemd.
Handling of sockets
What follows is a brief description of the process rsyslog takes to determine what system socket to use, which sockets rsyslog should listen on, whether the sockets should be created and how rsyslog should handle the sockets when shutting down.
Step 1: Select name of system socket
If the user has not explicitly chosen to set
SysSock.Use="off"then the default listener socket (aka, “system log socket” or simply “system socket”) name is set to/dev/log. Otherwise, if the user has explicitly setSysSock.Use="off", then rsyslog will not listen on/dev/logOR any socket defined by theSysSock.Nameparameter and the rest of this section does not apply.If the user has specified
sysSock.Name="/path/to/custom/socket"(and not explicitly setSysSock.Use="off"), then the default listener socket name is overwritten with/path/to/custom/socket.Otherwise, if rsyslog is running under systemd AND
/run/systemd/journal/syslogexists, (AND the user has not explicitly setSysSock.Use="off") then the default listener socket name is overwritten with/run/systemd/journal/syslog.
Step 2: Listen on specified sockets
Note
This is true for all sockets, be it system socket or not. But if SysSock.Use="off", the system socket will not be listened on.
rsyslog evaluates the list of sockets it has been asked to activate:
the system log socket (if still enabled after completion of the last section)
any custom inputs defined by the user
and then checks to see if it has been passed in via systemd (name is checked). If it was passed in via systemd, the socket is used as-is (e.g., not recreated upon rsyslog startup), otherwise if not passed in via systemd the log socket is unlinked, created and opened.
Step 3: Shutdown log sockets
Note
This is true for all sockets, be it system socket or not.
Upon shutdown, rsyslog processes each socket it is listening on and evaluates it. If the socket was originally passed in via systemd (name is checked), then rsyslog does nothing with the socket (systemd maintains the socket).
If the socket was not passed in via systemd AND the configuration permits rsyslog to do so (the default setting), rsyslog will unlink/remove the log socket. If not permitted to do so (the user specified otherwise), then rsyslog will not unlink the log socket and will leave that cleanup step to the user or application that created the socket to remove it.
Statistic Counter
This plugin maintains a global statistics with the following properties:
submitted- total number of messages submitted for processing since startupratelimit.discarded- number of messages discarded due to rate limitingratelimit.numratelimiters- number of currently active rate limiters (small data structures used for the rate limiting logic)
Caveats/Known Bugs
When running under systemd, many “sysSock.” parameters are ignored. See parameter descriptions and the Coexistence with systemd section for details.
On systems where systemd is used this module is often not loaded by default. See the Coexistence with systemd section for details.
Application timestamps are ignored by default. See the Control over application timestamps section for details.
Examples
Minimum setup
The following sample is the minimum setup required to accept syslog messages from applications running on the local system.
module(load="imuxsock")
This only needs to be done once.
Enable flow control
module(load="imuxsock" # needs to be done just once
SysSock.FlowControl="on") # enable flow control (use if needed)
Enable trusted properties
As noted in the Trusted (syslog) properties section, trusted properties
are disabled by default. If you want to use them, you must turn the feature
on via SysSock.Annotate for the system log socket and Annotate for
inputs.
Append to end of message
The following sample is used to activate message annotation and thus trusted properties on the system log socket. These trusted properties are appended to the end of each message.
module(load="imuxsock" # needs to be done just once
SysSock.Annotate="on")
Store in JSON message properties
The following sample is similar to the first one, but enables parsing of trusted properties, which places the results into JSON/lumberjack variables.
module(load="imuxsock"
SysSock.Annotate="on" SysSock.ParseTrusted="on")
Read log data from jails
The following sample is a configuration where rsyslogd pulls logs from two jails, and assigns different hostnames to each of the jails:
module(load="imuxsock") # needs to be done just once
input(type="imuxsock"
HostName="jail1.example.net"
Socket="/jail/1/dev/log") input(type="imuxsock"
HostName="jail2.example.net" Socket="/jail/2/dev/log")
Read from socket on temporary file system
The following sample is a configuration where rsyslogd reads the openssh log messages via a separate socket, but this socket is created on a temporary file system. As rsyslogd starts up before the sshd daemon, it needs to create the socket directories, because it otherwise can not open the socket and thus not listen to openssh messages.
module(load="imuxsock") # needs to be done just once
input(type="imuxsock"
Socket="/var/run/sshd/dev/log"
CreatePath="on")
Disable rate limiting
The following sample is used to turn off input rate limiting on the system log socket.
module(load="imuxsock" # needs to be done just once
SysSock.RateLimit.Interval="0") # turn off rate limiting
See also
Help with configuring/using Rsyslog:
Mailing list - best route for general questions
GitHub: rsyslog source project - detailed questions, reporting issues that are believed to be bugs with
Rsyslog
See also
Contributing to Rsyslog:
Source project: rsyslog project README.
Documentation: rsyslog-doc project README
Copyright 2008-2023 Rainer Gerhards (Großrinderfeld), and Others.