dynaFile

For each message, the file name is generated based on the given template.

This parameter applies to omfile: File Output Module.

Name:: dynaFile
Scope:: action
Type:: string
Default:: action=none
Required?:: no
Introduced:: at least 8.x, possibly earlier

Description

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 properly escapes every message-derived path component. In string templates, use the secpath-replace property replacer option. In list templates, use securePath="replace" on the corresponding property() statements. Apply this to all fields that can come from the message or sender, such as HOSTNAME, programname, APP-NAME, or parsed variables. Keep fixed directory separators in constant text.

By default, omfile also performs lexical containment checks for dynafile paths. The rendered path must remain below the fixed leading directory prefix that was configured in the dynafile template. This blocks remote path traversal through components such as .. or unexpected leading slashes in message-derived fields, but it is not a filesystem sandbox. It does not protect against symlinks, bind mounts, time-of-check/time-of-use races, or malicious local filesystem state. For untrusted inputs, secpath-replace or securePath="replace" remains the strongest recommended pattern.

Backward-compatibility change

Opaque legacy templates (subtree and plugin/string-generator templates) do not provide a fixed prefix that omfile can inspect. They remain supported, but their fallback guard rejects output paths that are absolute or lexically escape through ... This deliberately changes the historical behavior of affected legacy configurations. To preserve such a configuration temporarily, set dynafile.dangerousPermitPathEscape to on on the affected action (or module). That opt-in disables the guard for that action; use it only with trusted path data.

template(name="DynFile" type="string"
         string="/var/log/hosts/%HOSTNAME:::secpath-replace%/%programname:::secpath-replace%.log")

template(name="DynFileList" type="list") {
  constant(value="/var/log/hosts/")
  property(name="hostname" securePath="replace")
  constant(value="/")
  property(name="programname" securePath="replace")
  constant(value=".log")
}

When global(compatibility.defaults.secure="strict") is active, dynafile templates default fields without explicit secure path handling to secpath-replace. The warn setting keeps the historical default and emits a warning for dynafile templates that need an explicit securepath or secpath-* option. The backward-compatible setting keeps the historical default silently.

If the same template is used both for dynaFile and for non-dynafile output, rsyslog emits a warning. In strict mode the secure dynafile default still applies to that shared template. Use separate templates when non-dynafile output must preserve literal slashes.

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.

Action usage

action(type="omfile" dynaFile="...")

dynaFile

Description

Backward-compatibility change

Action usage

See also