omfile: File Output Module

Template

Set the default template to be used if an action is not configured to use a specific template.

DirCreateMode

Sets the default dirCreateMode to be used for an action if no explicit one is specified.

FileCreateMode

Sets the default fileCreateMode to be used for an action if no explicit one is specified.

fileOwner

Sets the default fileOwner to be used for an action if no explicit one is specified.

fileOwnerNum

Sets the default fileOwnerNum to be used for an action if no explicit one is specified.

fileGroup

Sets the default fileGroup to be used for an action if no explicit one is specified.

fileGroupNum

Sets the default fileGroupNum to be used for an action if no explicit one is specified.

dirOwner

Sets the default dirOwner to be used for an action if no explicit one is specified.

dirOwnerNum

Sets the default dirOwnerNum to be used for an action if no explicit one is specified.

dirGroup

Sets the default dirGroup to be used for an action if no explicit one is specified.

dirGroupNum

Sets the default dirGroupNum to be used for an action if no explicit one is specified.

dynafile.donotsuspend

This permits SUSPENDing dynafile actions. Traditionally, SUSPEND mode was never entered for dynafiles as it would have blocked overall processing flow. Default is not to suspend (and thus block).

compression.driver

For compressed operation (“zlib mode”), this permits to set the compression driver to be used. Originally, only zlib was supported and still is the default. Since 8.2208.0 zstd is also supported. It provides much better compression ratios and performance, especially with multiple zstd worker threads enabled.

Possible values are: - zlib - zstd

compression.zstd.workers

In zstd mode, this enables to configure zstd-internal compression worker threads. This setting has nothing to do with rsyslog workers. The zstd library provides an enhanced worker thread pool which permits multithreaed compression of serial data streams. Rsyslog fully supports this mode for optimal performance.

Please note that for this parameter to have an effect, the zstd library must be compiled with multithreading support. As of this writing (2022), this is not the case for many frequently used distros and distro versions. In this case, you may want to custom install the zstd library with threading enabled. Note that this does not require a rsyslog rebuild.

File

This creates a static file output, always writing into the same file. If the file already exists, new data is appended to it. Existing data is not truncated. If the file does not already exist, it is created. Files are kept open as long as rsyslogd is active. This conflicts with external log file rotation. In order to close a file after rotation, send rsyslogd a HUP signal after the file has been rotated away. Either file or dynaFile can be used, but not both. If both are given, dynaFile will be used.

dynaFile

For each message, the file name is generated based on the given template. Then, this file is opened. As with the file property, data is appended if the file already exists. If the file does not exist, a new file is created. The template given in “templateName” is just a regular rsyslog template, so you have full control over how to format the file name.

To avoid path traversal attacks, you must make sure that the template used properly escapes file paths. This is done by using the securepath parameter in the template’s property statements, or the secpath-drop or secpath-replace property options with the property replacer.

Either file or dynaFile can be used, but not both. If both are given, dynaFile will be used.

A cache of recent files is kept. Note that this cache can consume quite some memory (especially if large buffer sizes are used). Files are kept open as long as they stay inside the cache. Files are removed from the cache when a HUP signal is sent, the closeTimeout occurs, or the cache runs out of space, in which case the least recently used entry is evicted.

Template

Sets the template to be used for this action.

closeTimeout

Specifies after how many minutes of inactivity a file is automatically closed. Note that this functionality is implemented based on the janitor process. See its doc to understand why and how janitor-based times are approximate.

dynaFileCacheSize

This parameter specifies the maximum size of the cache for dynamically-generated file names (dynafile= parameter). This setting specifies how many open file handles should be cached. If, for example, the file name is generated with the hostname in it and you have 100 different hosts, a cache size of 100 would ensure that files are opened once and then stay open. This can be a great way to increase performance. If the cache size is lower than the number of different files, the least recently used one is discarded (and the file closed).

Note that this is a per-action value, so if you have multiple dynafile actions, each of them have their individual caches (which means the numbers sum up). Ideally, the cache size exactly matches the need. You can use impstats to tune this value. Note that a too-low cache size can be a very considerable performance bottleneck.

zipLevel

If greater than 0, turns on gzip compression of the output file. The higher the number, the better the compression, but also the more CPU is required for zipping.

veryRobustZip

If zipLevel is greater than 0, then this setting controls if extra headers are written to make the resulting file extra hardened against malfunction. If set to off, data appended to previously unclean closed files may not be accessible without extra tools (like gztool with: gztool -p). Note that this risk is usually expected to be bearable, and thus “off” is the default mode. The extra headers considerably degrade compression, files with this option set to “on” may be four to five times as large as files processed in “off” mode.

In order to avoid this degradation in compression both flushOnTXEnd and asyncWriting parameters must be set to “off” and also ioBufferSize must be raised from default “4k” value to at least “32k”. This way a reasonable compression factor is maintained, similar to a non-blocked gzip file:

veryRobustZip="on" ioBufferSize="64k" flushOnTXEnd="off" asyncWriting="off"

Do not forget to add your desired zipLevel to this configuration line.

flushInterval

Defines, in seconds, the interval after which unwritten data is flushed.

asyncWriting

If turned on, the files will be written in asynchronous mode via a separate thread. In that case, double buffers will be used so that one buffer can be filled while the other buffer is being written. Note that in order to enable FlushInterval, AsyncWriting must be set to “on”. Otherwise, the flush interval will be ignored.

flushOnTXEnd

Omfile has the capability to write output using a buffered writer. Disk writes are only done when the buffer is full. So if an error happens during that write, data is potentially lost. Bear in mind that the buffer may become full only after several hours or a rsyslog shutdown (however a buffer flush can still be forced by sending rsyslogd a HUP signal). In cases where this is unacceptable, set FlushOnTXEnd to “on”. Then, data is written at the end of each transaction (for pre-v5 this means after each log message) and the usual error recovery thus can handle write errors without data loss. Note that this option severely reduces the effect of zip compression and should be switched to “off” for that use case. Also note that the default -on- is primarily an aid to preserve the traditional syslogd behaviour.

If you are using dynamic file names (dynafiles), flushes can actually happen more frequently. In this case, a flush can also happen when the file name changes within a transaction.

ioBufferSize

Size of the buffer used to writing output data. The larger the buffer, the potentially better performance is. The default of 4k is quite conservative, it is useful to go up to 64k, and 128k if you used gzip compression (then, even higher sizes may make sense)

dirOwner

Set the file owner for directories newly created. Please note that this setting does not affect the owner of directories already existing. 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.

dirOwnerNum

Set the file owner for directories newly created. Please note that this setting does not affect the owner of directories already existing. The parameter is a numerical ID, 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.

dirGroup

Set the group for directories newly created. Please note that this setting does not affect the group of directories already existing. The parameter is a group name, for which the groupid is obtained by rsyslogd on during startup processing. Interim changes to the user mapping are not detected.

dirGroupNum

Set the group for directories newly created. Please note that this setting does not affect the group of directories already existing. 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.

fileOwner

Set the file owner for files newly created. Please note that this setting does not affect the owner of files already existing. 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

Set the file owner for files newly created. Please note that this setting does not affect the owner of files already existing. 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

Set the group for files newly created. Please note that this setting does not affect the group of files already existing. 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

Set the group for files newly created. Please note that this setting does not affect the group of files already existing. 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

The FileCreateMode directive allows to specify the creation mode with which rsyslogd creates new files. If not specified, the value 0644 is used (which retains backward-compatibility with earlier releases). 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.

dirCreateMode

This is the same as FileCreateMode, but for directories automatically generated.

failOnChOwnFailure

This option modifies behaviour of file creation. If different owners or groups are specified for new files or directories and rsyslogd fails to set these new owners or groups, it will log an error and NOT write to the file in question if that option is set to “on”. If it is set to “off”, the error will be ignored and processing continues. Keep in mind, that the files in this case may be (in)accessible by people who should not have permission. The default is “on”.

createDirs

Create directories on an as-needed basis

sync

Enables file syncing capability of omfile.

When enabled, rsyslog does a sync to the data file as well as the directory it resides after processing each batch. There currently is no way to sync only after each n-th batch.

Enabling sync causes a severe performance hit. Actually, it slows omfile so much down, that the probability of loosing messages increases. In short, you should enable syncing only if you know exactly what you do, and fully understand how the rest of the engine works, and have tuned the rest of the engine to lossless operations.

sig.Provider

Selects a signature provider for log signing. By selecting a provider, the signature feature is turned on.

Currently there is one signature provider available: “ksi_ls12”.

Previous signature providers “gt” and “ksi” are deprecated.

cry.Provider

Selects a crypto provider for log encryption. By selecting a provider, the encryption feature is turned on.

Currently, there are two providers called “gcry” and “ossl”.

rotation.sizeLimit

This permits to set a size limit on the output file. When the limit is reached, rotation of the file is tried. The rotation script needs to be configured via rotation.sizeLimitCommand.

Please note that the size limit is not exact. Some excess bytes are permitted to prevent messages from being split across two files. Also, a full batch of messages is not terminated in between. As such, in practice, the size of the output file can grow some KiB larger than configured.

Also avoid to configer a too-low limit, especially for busy files. Calling the rotation script is relatively performance intense. As such, it could negatively affect overall rsyslog performance.

rotation.sizeLimitCommand

This permits to configure the script to be called whe a size limit on the output file is reached. The actual size limit needs to be configured via rotation.sizeLimit.