This driver starts an external application or script and sends the log messages to its standard input (stdin
).
The program()
destination has the following options:
disk-buffer()
Description: This option enables putting outgoing messages into the disk buffer of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:
capacity-bytes()
Type: | number (bytes) |
---|---|
Default: | 1MiB |
Description: This is a required option. The maximum size of the disk-buffer in bytes. The minimum value is 1048576
bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old log-disk-fifo-size()
option.
In AxoSyslog version 4.2 and earlier, this option was called disk-buf-size()
.
compaction()
Type: | yes/no |
---|---|
Default: | no |
Description: If set to yes
, AxoSyslog prunes the unused space in the LogMessage representation, making the disk queue size smaller at the cost of some CPU time. Setting the compaction()
argument to yes
is recommended when numerous name-value pairs are unset during processing, or when the same names are set multiple times.
unset()
rewrite operation is not enough, as due to performance reasons that help when AxoSyslog is CPU bound, the internal representation of a LogMessage
will not release the memory associated with these name-value pairs. In some cases, however, the size of this overhead becomes significant (the raw message size can grow up to four times its original size), which unnecessarily increases the disk queue file size. For these cases, the compaction will drop unset
values, making the LogMessage
representation smaller at the cost of some CPU time required to perform compaction.
dir()
Type: | string |
---|---|
Default: | N/A |
Description: Defines the folder where the disk-buffer files are stored.
When creating a new dir()
option for a disk buffer, or modifying an existing one, make sure you delete the persist file.
AxoSyslog creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir()
option, then following a restart, AxoSyslog will look for or create disk-buffer files in their old location. To ensure that AxoSyslog uses the new dir()
setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.
dir()
path provided by the user does not exist, AxoSyslog creates the path with the same permission as the running instance.
flow-control-window-bytes()
Type: | number (bytes) |
---|---|
Default: | 163840000 |
Description: Use this option if the option reliable()
is set to yes
. This option contains the size of the messages in bytes that is used in the memory part of the disk buffer. It replaces the old log-fifo-size()
option. It does not inherit the value of the global log-fifo-size()
option, even if it is provided. Note that this option will be ignored if the option reliable()
is set to no
.
In AxoSyslog version 4.2 and earlier, this option was called mem-buf-size()
.
flow-control-window-size()
Type: | number(messages) |
---|---|
Default: | 10000 |
Description: Use this option if the option reliable()
is set to no
. This option contains the number of messages stored in overflow queue. It replaces the old log-fifo-size()
option. It inherits the value of the global log-fifo-size()
option if provided. If it is not provided, the default value is 10000
messages. Note that this option will be ignored if the option reliable()
is set to yes
.
In AxoSyslog version 4.2 and earlier, this option was called mem-buf-length()
.
front-cache-size()
Type: | number(messages) |
---|---|
Default: | 1000 |
Description: The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer already exists, the change will take effect when the disk-buffer becomes empty.
Options reliable()
and capacity-bytes()
are required options.
In AxoSyslog version 4.2 and earlier, this option was called qout-size()
.
prealloc()
Type: | yes/no |
---|---|
Default: | no |
Description:
By default, AxoSyslog doesn’t reserve the disk space for the disk-buffer file, since in a properly configured and sized environment the disk-buffer is practically empty, so a large preallocated disk-buffer file is just a waste of disk space. But a preallocated buffer can prevent other data from using the intended buffer space (and elicit a warning from the OS if disk space is low), preventing message loss if the buffer is actually needed. To avoid this problem, when using AxoSyslog 4.0 or later, you can preallocate the space for your disk-buffer files by setting prealloc(yes)
.
In addition to making sure that the required disk space is available when needed, preallocated disk-buffer files provide radically better (3-4x) performance as well: in case of an outage the amount of messages stored in the disk-buffer is continuously growing, and using large continuous files is faster, than constantly waiting on a file to change its size.
If you are running AxoSyslog on a dedicated host (always recommended for any high-volume settings), use prealloc(yes)
.
Available in AxoSyslog 4.0 and later.
reliable()
Type: | yes/no |
---|---|
Default: | no |
Description: If set to yes
, AxoSyslog cannot lose logs in case of reload/restart, unreachable destination or AxoSyslog crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no
, the normal disk-buffer will be used. This provides a faster, but less reliable disk-buffer option.
reliable()
option when there are messages in the disk-buffer, the messages stored in the disk-buffer will be lost.
truncate-size-ratio()
Type: | number((between 0 and 1)) |
---|---|
Default: | 1 (do not truncate) |
Description: Limits the truncation of the disk-buffer file. Truncating the disk-buffer file can slow down the disk IO operations, but it saves disk space. By default, AxoSyslog version 4.0 and later doesn’t truncate disk-buffer files by default (truncate-size-ratio(1)
). Earlier versions freed the disk-space when at least 10% of the disk-buffer file could be freed (truncate-size-ratio(0.1)
).
AxoSyslog only truncates the file if the possible disk gain is more than truncate-size-ratio()
times capacity-bytes()
.
- Smaller values free disk space quicker.
- Larger ratios result in better performance.
If you want to avoid performance fluctuations:
- use
truncate-size-ratio(1)
(never truncate), or - use
prealloc(yes)
to reserve the entire size of the disk-buffer on disk.
truncate-size-ratio()
. Only change its value if you understand the performance implications of doing so.
Example: Examples for using disk-buffer()
In the following case reliable disk-buffer() is used.
destination d_demo {
network(
"127.0.0.1"
port(3333)
disk-buffer(
flow-control-window-bytes(10000)
capacity-bytes(2000000)
reliable(yes)
dir("/tmp/disk-buffer")
)
);
};
In the following case normal disk-buffer() is used.
destination d_demo {
network(
"127.0.0.1"
port(3333)
disk-buffer(
flow-control-window-size(10000)
capacity-bytes(2000000)
reliable(no)
dir("/tmp/disk-buffer")
)
);
};
flags()
Type: | no-multi-line, syslog-protocol |
Default: | empty set |
Description: Flags influence the behavior of the destination driver.
- no-multi-line: The
no-multi-line
flag disables line-breaking in the messages: the entire message is converted to a single line. - syslog-protocol: The
syslog-protocol
flag instructs the driver to format the messages according to the new IETF syslog protocol standard (RFC5424), but without the frame header. If this flag is enabled, macros used for the message have effect only for the text of the message, the message header is formatted to the new standard. Note that this flag is not needed for thesyslog
driver, and that thesyslog
driver automatically adds the frame header to the messages.
flush-lines()
Type: | number |
Default: | Use global setting (exception: for http() destination, the default is 1). |
Description: Specifies how many lines are flushed to a destination at a time. The AxoSyslog application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency.
The AxoSyslog application flushes the messages if it has sent flush-lines()
number of messages, or the queue became empty. If you stop or reload AxoSyslog or in case of network sources, the connection with the client is closed, AxoSyslog automatically sends the unsent messages to the destination.
For optimal performance when sending messages to an AxoSyslog server, make sure that the value of flush-lines()
is smaller than the window size set in the log-iw-size()
option in the source of your server.
frac-digits()
Type: | number |
Default: | 0 |
Description: The AxoSyslog application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits()
parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received.
frac-digits()
option is set to a value higher than 6, AxoSyslog will truncate the fraction seconds in the timestamps after 6 digits.
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.
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")
)
);
};
log-fifo-size()
Type: | number |
Default: | Use global setting. |
Description: The number of messages that the output queue can store.
inherit-environment()
Type: | `yes |
Default: | yes |
Description: By default, when program()
starts an external application or script, it inherits the entire environment of the parent process (that is, AxoSyslog). Use inherit-environment(no)
to prevent this.
keep-alive()
Type: | yes or no |
Default: | no |
Description: Specifies whether the external program should be closed when AxoSyslog is reloaded.
mark-freq()
Accepted values: | number [seconds] |
Default: | 1200 |
Description: An alias for the obsolete mark()
option, retained for compatibility with version 1.6.x.
The number of seconds between two MARK
messages. MARK
messages are generated when there was no message traffic to inform the receiver that the connection is still alive. If set to zero (0
), no MARK
messages are sent. The mark-freq()
can be set for global option and/or every MARK
capable destination driver if mark-mode()
is periodical or dst-idle or host-idle. If mark-freq()
is not defined in the destination, then the mark-freq()
will be inherited from the global options. If the destination uses internal mark-mode()
, then the global mark-freq()
will be valid (does not matter what mark-freq()
set in the destination side).
mark-mode()
Accepted values: | internal | dst-idle | host-idle | periodical | none | global |
Default: |
|
Description: The mark-mode()
option can be set for the following destination drivers: file(), program(), unix-dgram(), unix-stream(), network(), pipe(), syslog() and in global option.
-
internal
: When internal mark mode is selected, internal source should be placed in the log path as this mode does not generate mark by itself at the destination. This mode only yields the mark messages from internal source. This is the mode as AxoSyslog 3.3 worked.MARK
will be generated by internal source if there was NO traffic on local sources:file()
,pipe()
,unix-stream()
,unix-dgram()
,program()
-
dst-idle
: SendsMARK
signal if there was NO traffic on destination drivers.MARK
signal from internal source will be dropped.MARK
signal can be sent by the following destination drivers:network()
,syslog()
,program()
,file()
,pipe()
,unix-stream()
,unix-dgram()
. -
host-idle
: SendsMARK
signal if there was NO local message on destination drivers. for example,MARK
is generated even if messages were received from tcp.MARK
signal from internal source will be dropped.MARK
signal can be sent by the following destination drivers:network()
,syslog()
,program()
,file()
,pipe()
,unix-stream()
,unix-dgram()
. -
periodical
: SendsMARK
signal perodically, regardless of traffic on destination driver.MARK
signal from internal source will be dropped.MARK
signal can be sent by the following destination drivers:network()
,syslog()
,program()
,file()
,pipe()
,unix-stream()
,unix-dgram()
. -
none
: Destination driver drops allMARK
messages. If an explicit mark-mode() is not given to the drivers wherenone
is the default value, thennone
will be used. -
global
: Destination driver uses the globalmark-mode()
setting. Note that setting the globalmark-mode()
to global causes a syntax error in AxoSyslog.
dst-idle
, host-idle
and periodical
, the MARK
message will not be written in the destination, if it is not open yet.
Available in AxoSyslog 3.4 and later.
Note that in earlier versions of AxoSyslog, the default for the mark-mode of the program
destination was none
. Now it defaults to the global setting, so the program
destination will emit a MARK message every mark-freq
interval. To avoid such messages, set the mark-mode()
option of the destination to none
.
suppress()
Type: | seconds |
Default: | 0 (disabled) |
Description: If several identical log messages would be sent to the destination without any other messages between the identical messages (for example, an application repeated an error message ten times), AxoSyslog can suppress the repeated messages and send the message only once, followed by the Last message repeated n times.
message. The parameter of this option specifies the number of seconds AxoSyslog waits for identical messages.
template()
Type: | string |
Default: | A format conforming to the default logfile format. |
Description: Specifies a template defining the logformat to be used in the destination. Macros are described in Macros of AxoSyslog. Please note that for network destinations it might not be appropriate to change the template as it changes the on-wire format of the syslog protocol which might not be tolerated by stock syslog receivers (like syslogd
or syslog-ng
itself). For network destinations make sure the receiver can cope with the custom format defined.
Make sure to end your template with a newline character (\n
).
template-escape()
Type: | yes or no |
Default: | no |
Description: Turns on escaping for the '
, "
, and backspace characters in templated output files. This is useful for generating SQL statements and quoting string contents so that parts of the log message are not interpreted as commands to the SQL server.
Note: Starting with AxoSyslog version 4.5,
template-escape(yes)
escapes the top-level template function in case of nested template functions.
throttle()
Type: | number |
Default: | 0 |
Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using disk-buffer as well to avoid the risk of losing messages. Specifying 0
or a lower value sets the output limit to unlimited.
time-reopen()
Accepted values: | number [seconds] |
Default: | 60 |
Description: The time to wait in seconds before a dead connection is reestablished.
time-zone()
Type: | name of the timezone, or the timezone offset |
Default: | unspecified |
Description: Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, HOUR
. For the complete list of such macros, see Date-related macros.
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.
ts-format()
Type: | rfc3164, bsd, rfc3339, iso |
Default: | rfc3164 |
Description: Override the global timestamp format (set in the global ts-format()
parameter) for the specific destination. For details, see ts-format().
network()
, or syslog()
) ignore this option. For protocol-like destinations, use a template locally in the destination, or use the proto-template option.