Appenders

Appenders are responsible for delivering log events to their destination. Every Appender must implement the IAppender interface.

While not strictly required by the log4net architecture, most appenders inherit from AppenderSkeleton and:

delegate the filtering of log events to an implementation of IFilter. See Filters for more information.
delegate the formatting of log events to an implementation of ILayout. See Layouts for more information.
only directly handle the writing of log event data to the target destination.

Appenders always have a name so that they can be referenced from a logger configuration.

List of appenders

log4net ships with the following appenders

Type	Description
AdoNetAppender	Writes logging events to a database using either prepared statements or stored procedures.
AnsiColorTerminalAppender	Writes color highlighted logging events to a an ANSI terminal window.
AspNetTraceAppender	Writes logging events to the ASP trace context. These can then be rendered at the end of the ASP page or on the ASP trace page.
BufferingForwardingAppender	Buffers events and then forwards them to attached appenders.
ColoredConsoleAppender	Writes color highlighted logging events to the application’s Windows Console.
ConsoleAppender	Writes logging events to the application’s Console. The events may go to either the standard our stream or the standard error stream.
DebugAppender	Writes logging events to the .net debugger (System.Diagnostics.Debug).
EventLogAppender	Writes logging events to the Windows Event Log.
FileAppender	Writes logging events to a file in the file system.
LocalSyslogAppender	Writes logging events to the local syslog service (UNIX only).
ManagedColoredConsoleAppender	Writes color highlighted logging events to the application’s Windows Console. This appender is a managed version of the ColoredConsoleAppender and does not require the use of the Windows Console API. It is a replacement for the ColoredConsoleAppender and is the recommended appender for logging to the Console.
MemoryAppender	Stores logging events in an in memory buffer.
OutputDebugStringAppender	Writes logging events to the debugger (using OutputDebugString). If the application has no debugger, the system debugger displays the string. If the application has no debugger and the system debugger is not active, the message is ignored.
RemoteSyslogAppender	Writes logging events to a remote syslog service using UDP networking.
RollingFileAppender	Writes logging events to a file in the file system. The RollingFileAppender can be configured to log to multiple files based upon date or file size constraints.
SmtpAppender	Sends logging events to an email address.
SmtpPickupDirAppender	Sends logging events to an email address but writes the emails to a configurable directory rather than sending them directly via SMTP.
TelnetAppender	Clients connect via Telnet to receive logging events.
TraceAppender	Writes logging events to the .NET trace system (System.Diagnostics.Trace).
UdpAppender	Sends logging events as connectionless UDP datagrams to a remote host or a multicast group using a UdpClient.
ForwardingAppender	Can be used to wrap another appender, for example to attach additional filters.

Type

Description

AdoNetAppender

Writes logging events to a database using either prepared statements or stored procedures.

AnsiColorTerminalAppender

Writes color highlighted logging events to a an ANSI terminal window.

AspNetTraceAppender

Writes logging events to the ASP trace context. These can then be rendered at the end of the ASP page or on the ASP trace page.

BufferingForwardingAppender

Buffers events and then forwards them to attached appenders.

ColoredConsoleAppender

Writes color highlighted logging events to the application’s Windows Console.

ConsoleAppender

Writes logging events to the application’s Console. The events may go to either the standard our stream or the standard error stream.

DebugAppender

Writes logging events to the .net debugger (System.Diagnostics.Debug).

EventLogAppender

Writes logging events to the Windows Event Log.

FileAppender

Writes logging events to a file in the file system.

LocalSyslogAppender

Writes logging events to the local syslog service (UNIX only).

ManagedColoredConsoleAppender

Writes color highlighted logging events to the application’s Windows Console. This appender is a managed version of the ColoredConsoleAppender and does not require the use of the Windows Console API. It is a replacement for the ColoredConsoleAppender and is the recommended appender for logging to the Console.

MemoryAppender

Stores logging events in an in memory buffer.

OutputDebugStringAppender

Writes logging events to the debugger (using OutputDebugString). If the application has no debugger, the system debugger displays the string. If the application has no debugger and the system debugger is not active, the message is ignored.

RemoteSyslogAppender

Writes logging events to a remote syslog service using UDP networking.

RollingFileAppender

Writes logging events to a file in the file system. The RollingFileAppender can be configured to log to multiple files based upon date or file size constraints.

SmtpAppender

Sends logging events to an email address.

SmtpPickupDirAppender

Sends logging events to an email address but writes the emails to a configurable directory rather than sending them directly via SMTP.

TelnetAppender

Clients connect via Telnet to receive logging events.

TraceAppender

Writes logging events to the .NET trace system (System.Diagnostics.Trace).

UdpAppender

Sends logging events as connectionless UDP datagrams to a remote host or a multicast group using a UdpClient.

ForwardingAppender

Can be used to wrap another appender, for example to attach additional filters.

Appender Additivity

A logger can have multiple appenders.

Each enabled logging request is passed to all appenders attached to that logger, and also to appenders higher in the logger hierarchy. This behavior is called appender additivity and is enabled by default.

For example, if a console appender is attached to the root logger, all enabled logs will at least print to the console. If a file appender is added to logger X, logs from X and its children will go to both the file and the console.

Additivity can be disabled by setting a logger’s additivity flag to false. This prevents logging events from being passed to ancestor appenders beyond that point.

If the Animals logger has additivity = false, then the Animals.Carnivora logger will only send its log messages to its own appenders and to Animals’ appenders— but not to any appenders higher up in the hierarchy, such as those on the root logger.

Logger Name	Added Appenders	Additivity Flag	Output Targets	Comment
root	ConsoleAppender	not applicable	ConsoleAppender	Default appender at the root.
Animals	FileAppender, RollingFileAppender	true	ConsoleAppender, FileAppender, RollingFileAppender	Appenders of "Animals" and root.
Animals.Carnivora	none	true	ConsoleAppender, FileAppender, RollingFileAppender	Inherited from "Animals" and root.
Animals.Carnivora.Felidae	SmtpAppender	true	ConsoleAppender, FileAppender, RollingFileAppender, SmtpAppender	Appenders in "Animals.Carnivora.Felidae", "Animals", and root.
Security	UdpAppender	false	UdpAppender	No appender accumulation because additivity is set to false.
Security.Access	none	true	UdpAppender	Only appenders of "Security" are used due to disabled additivity in "Security".

Logger Name

Added Appenders

Additivity Flag

Output Targets

Comment

root

ConsoleAppender

not applicable

ConsoleAppender

Default appender at the root.

Animals

FileAppender, RollingFileAppender

true

ConsoleAppender, FileAppender, RollingFileAppender

Appenders of "Animals" and root.

Animals.Carnivora

none

true

ConsoleAppender, FileAppender, RollingFileAppender

Inherited from "Animals" and root.

Animals.Carnivora.Felidae

SmtpAppender

true

ConsoleAppender, FileAppender, RollingFileAppender, SmtpAppender

Appenders in "Animals.Carnivora.Felidae", "Animals", and root.

Security

UdpAppender

false

UdpAppender

No appender accumulation because additivity is set to false.

Security.Access

none

true

UdpAppender

Only appenders of "Security" are used due to disabled additivity in "Security".