This section describes the options of the file() destination in syslog-ng OSE.

The file() destination has the following options:

CAUTION: When creating several thousands separate log files, syslog-ng Open Source Edition (syslog-ng OSE) might not be able to open the required number of files. This might happen for example, when using the ${HOST} macro in the filename while receiving messages from a large number of hosts. To overcome this problem, adjust the –fd-limit command-line parameter of syslog-ng OSE or the global ulimit parameter of your host. For setting the –fd-limit command-line parameter ofsyslog-ng OSE see the The syslog-ng OSE manual page. For setting the ulimit parameter of the host, see the documentation of your operating system.

create-dirs()

Accepted values: yes or no
Default: no

Description: Enable creating non-existing directories when creating files or socket files.

NOTE: If syslog-ng cannot create the pipe, it aborts and produces an error. This could be caused by the lack of a write permission, or missing directory. The latter of the two can be fixed by using the create-dirs(yes) option.

dir-group()

Accepted values: groupid
Default: Use the global settings

Description: The group of the directories created by syslog-ng. To preserve the original properties of an existing directory, use the option without specifying an attribute: dir-group().

dir-owner()

Accepted values: userid
Default: Use the global settings

Description: The owner of the directories created by syslog-ng. To preserve the original properties of an existing directory, use the option without specifying an attribute: dir-owner().

Starting with version 3.16, the default value of this option is -1, so syslog-ng OSE does not change the ownership, unless explicitly configured to do so.

dir-perm()

Accepted values: permission value
Default: Use the global settings

Description: The permission mask of directories created by syslog-ng. Log directories are only created if a file after macro expansion refers to a non-existing directory, and directory creation is enabled (see also the create-dirs() option). For octal numbers prefix the number with 0, for example, use 0755 for rwxr-xr-x.

To preserve the original properties of an existing directory, use the option without specifying an attribute: dir-perm(). Note that when creating a new directory without specifying attributes for dir-perm(), the default permission of the directories is masked with the umask of the parent process (typically 0022).

Starting with version 3.16, the default value of this option is -1, so syslog-ng OSE does not change the ownership, unless explicitly configured to do so.

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 suboptions:

capacity-bytes()

Type: number (bytes)
Default: 1 MiB

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 syslog-ng OSE version 4.2 and earlier, this option was called disk-buf-size().

compaction()

Type: yes/no
Default: no

Description: If set to yes, syslog-ng OSE 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.

NOTE: Simply unsetting these name-value pairs by using the unset() rewrite operation is not enough, as due to performance reasons that help when syslog-ng OSE 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.

CAUTION: When creating a new dir() option for a disk buffer, or modifying an existing one, make sure you delete the persist file.

syslog-ng OSE 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, syslog-ng OSE will look for or create disk-buffer files in their old location. To ensure that syslog-ng OSE 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.

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 syslog-ng OSE 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 syslog-ng OSE 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 syslog-ng OSE version 4.2 and earlier, this option was called qout-size().

prealloc()

Type: yes/no
Default: no

Description: By default, syslog-ng OSE 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 syslog-ng OSE 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 syslog-ng OSE on a dedicated host (always recommended for any high-volume settings), use prealloc(yes).

Available in syslog-ng OSE 4.0 and later.

reliable()

Type: yes/no
Default: no

Description: If set to yes, syslog-ng OSE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng OSE 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.

CAUTION: Hazard of data loss! If you change the value of 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, syslog-ng OSE 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)).

syslog-ng OSE 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.

CAUTION: It is not recommended to change 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, threaded
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 (RFC-5424), 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 the syslog driver, and that the syslog driver automatically adds the frame header to the messages.

  • threaded: The threaded flag enables multithreading for the destination. For details on multithreading, see Multithreading and scaling in syslog-ng OSE.

    NOTE: The file destination uses multiple threads only if the destination filename contains macros.

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 syslog-ng OSE 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 syslog-ng OSE application flushes the messages if it has sent flush-lines() number of messages, or the queue became empty. If you stop or reload syslog-ng OSE or in case of network sources, the connection with the client is closed, syslog-ng OSE automatically sends the unsent messages to the destination.

For optimal performance when sending messages to an syslog-ng OSE 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 syslog-ng OSE 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.

NOTE: The syslog-ng OSE application can add the fractions to non-ISO8601 timestamps as well.

NOTE: As syslog-ng OSE is precise up to the microsecond, when the frac-digits() option is set to a value higher than 6, syslog-ng OSE will truncate the fraction seconds in the timestamps after 6 digits.

fsync()

Type: yes or no
Default: no

Description: Forces an fsync() call on the destination fd after each write.

NOTE: Enabling this option may seriously degrade performance.

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 syslog-ng OSE 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 syslog-ng OSE to execute external applications.

Using the hook-commands() when syslog-ng OSE starts or stops

To execute an external program when syslog-ng OSE starts or stops, use the following options:

startup()

Type: string
Default: N/A

Description: Defines the external program that is executed as syslog-ng OSE starts.

shutdown()

Type: string
Default: N/A

Description: Defines the external program that is executed as syslog-ng OSE stops.

Using the hook-commands() when syslog-ng OSE reloads

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

setup()

Type: string
Default: N/A

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

teardown()

Type: string
Default: N/A

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

Example: Using the 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 syslog-ng OSE 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 syslog-ng OSE 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")
        )
      );
};

group()

Type: string
Default: Use the global settings

Description: Set the group of the created file to the one specified. To preserve the original properties of an existing file, use the option without specifying an attribute: group().

local-time-zone()

Type: name of the timezone, or the timezone offset
Default: The local timezone.

Description: Sets the timezone used when expanding filename and tablename templates.

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.

log-fifo-size()

Type: number
Default: Use global setting.

Description: The number of messages that the output queue can store.

mark-freq()

Accepted values: number [seconds]
Default: 1200

Description: An alias for the obsolete mark() option, retained for compatibility with syslog-ng OSE 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: internal for pipe, program drivers, none for file, unix-dgram, unix-stream drivers, global for syslog, tcp, udp destinations, host-idle for global option  

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.

NOTE: In case of dst-idle, host-idle and periodical, the MARK message will not be written in the destination, if it is not open yet.

Available in syslog-ng OSE 3.4 and later.

overwrite-if-older()

Type: number (seconds)
Default: 0

Description: If set to a value higher than 0, syslog-ng OSE checks when the file was last modified before starting to write into the file. If the file is older than the specified amount of time (in seconds), then syslog-ng OSE removes the existing file and opens a new file with the same name. In combination with for example, the ${WEEKDAY} macro, this can be used for simple log rotation, in case not all history has to be kept. (Note that in this weekly log rotation example if its Monday 00:01, then the file from last Monday is not seven days old, because it was probably last modified shortly before 23:59 last Monday, so it is actually not even six days old. So in this case, set the overwrite-if-older() parameter to a-bit-less-than-six-days, for example, to 518000 seconds.

owner()

Type: string
Default: Use the global settings

Description: Set the owner of the created file to the one specified. To preserve the original properties of an existing file, use the option without specifying an attribute: owner().

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 syslog-ng OSE 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(), syslog-ng OSE will not read anymore from this pipe and displays the following error message:

Padding was set, and couldn’t read enough bytes

CAUTION: Hazard of data loss! If the size of the incoming message is larger than the previously set pad-size() value, syslog-ng OSE will truncate the message to the specified size. Therefore, all message content above that size will be lost.

perm()

Type: number (octal notation)
Default: 0600

Description: Sets the permission mask. For octal numbers prefix the number with 0, for example: use 0755 for rwxr-xr-x.

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), syslog-ng OSE 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 syslog-ng OSE waits for identical messages.

Type: Filename
Default: N/A

Description: The configured file name will be used as a symbolic link to the last created file by file destination.

An example when time-based macro is used:

file("/var/log/cron.${YEAR}${MONTH}" symlink-as("/var/log/cron"));

In this case the /var/log/cron should point to the current month.

NOTE: The symlink uses the same permissions as the file destination.

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 syslog-ng OSE. 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 OSE itself). For network destinations make sure the receiver can cope with the custom format defined.

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: In syslog-ng OSE 4.5 and later versions template-escape(yes) escapes the top-level template function in case of nested template functions.

time-reap()

Accepted values: number (seconds)
Default: 60 or 0, see description for details

Description: The time to wait in seconds before an idle destination file or pipe is closed. Note that only destination files having macros in their filenames are closed automatically.

Starting with version 3.23, the way how time-reap() works is the following.

  1. If the time-reap() option of the destination is set, that value is used, for example:

     destination d_fifo {
     pipe(
         "/tmp/test.fifo",
         time-reap(30)  # sets time-reap() for this destination only
     );
 };

  2. If the time-reap() option of the destination is not set, and the destination does not use a template or macro in its filename or path, time-reap() is automatically set to 0. For example:

     destination d_fifo {
     pipe(
         "/tmp/test.fifo",
     );
 };

  3. Otherwise, the value of the global time-reap() option is used, which defaults to 60 seconds.

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:  

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.

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().

NOTE: This option applies only to file and file-like destinations. Destinations that use specific protocols (for example, network(), or syslog()) ignore this option. For protocol-like destinations, use a template locally in the destination, or use the proto-template() option.

Updated: