solr/solr-ref-guide/src/defining-core-properties.adoc

= Defining core.properties
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Core discovery means that creating a core is as simple as a `core.properties` file located on disk.

The `core.properties` file is a simple Java Properties file where each line is just a key=value pair, e.g., `name=core1`. Notice that no quotes are required.

A minimal `core.properties` file looks like the example below. However, it can also be empty, see information on placement of `core.properties` below.

[source,bash]
----
name=my_core_name
----

== Placement of core.properties

Solr cores are configured by placing a file named `core.properties` in a sub-directory under `solr.home`. There are no a-priori limits to the depth of the tree, nor are there limits to the number of cores that can be defined. Cores may be anywhere in the tree with the exception that cores may _not_ be defined under an existing core. That is, the following is not allowed:

[source,text]
----
./cores/core1/core.properties
./cores/core1/coremore/core5/core.properties
----

In this example, the enumeration will stop at "core1".

The following is legal:

[source,text]
----
./cores/somecores/core1/core.properties
./cores/somecores/core2/core.properties
./cores/othercores/core3/core.properties
./cores/extracores/deepertree/core4/core.properties
----

It is possible to segment Solr into multiple cores, each with its own configuration and indices. Cores may be dedicated to a single application or to very different ones, but all are administered through a common administration interface. You can create new Solr cores on the fly, shutdown cores, even replace one running core with another, all without ever stopping or restarting Solr.

Your `core.properties` file can be empty if necessary. Suppose `core.properties` is located in `./cores/core1` (relative to `solr_home`) but is empty. In this case, the core name is assumed to be "core1". The instanceDir will be the folder containing `core.properties` (i.e., `./cores/core1`). The dataDir will be `../cores/core1/data`, etc.

[NOTE]
====
You can run Solr without configuring any cores.
====

== Defining core.properties Files

The minimal `core.properties` file is an empty file, in which case all of the properties are defaulted appropriately.

Java properties files allow the hash (`#`) or bang (`!`) characters to specify comment-to-end-of-line.

The following properties are available:

`name`:: The name of the SolrCore. You'll use this name to reference the SolrCore when running commands with the CoreAdminHandler.

`config`:: The configuration file name for a given core. The default is `solrconfig.xml`.

`schema`:: The schema file name for a given core. The default is `schema.xml` but please note that if you are using a "managed schema" (the default behavior) then any value for this property which does not match the effective `managedSchemaResourceName` will be read once, backed up, and converted for managed schema use. See <<schema-factory-definition-in-solrconfig.adoc#,Schema Factory Definition in SolrConfig>> for more details.

`dataDir`:: The core's data directory (where indexes are stored) as either an absolute pathname, or a path relative to the value of `instanceDir`. This is `data` by default.

`configSet`:: The name of a defined configset, if desired, to use to configure the core (see the section  <<config-sets.adoc#,Configsets>> for more details).

`properties`:: The name of the properties file for this core. The value can be an absolute pathname or a path relative to the value of `instanceDir`.

`transient`:: If *true*, the core can be unloaded if Solr reaches the `transientCacheSize`. The default if not specified is *false*. Cores are unloaded in order of least recently used first. _Setting this to *true* is not recommended in SolrCloud mode._

`loadOnStartup`:: If *true*, the default if it is not specified, the core will loaded when Solr starts. _Setting this to *false* is not recommended in SolrCloud mode._

`coreNodeName`:: Used only in SolrCloud, this is a unique identifier for the node hosting this replica. By default a `coreNodeName` is generated automatically, but setting this attribute explicitly allows you to manually assign a new core to replace an existing replica. For example, this can be useful when replacing a machine that has had a hardware failure by restoring from backups on a new machine with a new hostname or port.

`ulogDir`:: The absolute or relative directory for the update log for this core (SolrCloud).

`shard`:: The shard to assign this core to (SolrCloud).

`collection`:: The name of the collection this core is part of (SolrCloud).

`roles`:: Future parameter for SolrCloud or a way for users to mark nodes for their own use.

Additional user-defined properties may be specified for use as variables. For more information on how to define local properties, see the section <<configuring-solrconfig-xml.adoc#substituting-properties-in-solr-config-files,Substituting Properties in Solr Config Files>>.