# Customize ES Systems[](https://wiki.batocera.org/emulationstation:customize_systems#customize_es_systems)

EmulationStation displays systems based on a file called  `es_systems.cfg`. In other distributions, this is typically the only file. However, in Batocera  the  `/userdata/system/configs/emulationstation/es_systems_<custom_name>.cfg`  can be used as an overlay to the original  `/usr/share/emulationstation/es_systems.cfg`  file.

> If preferred, the entire file can be overridden by instead using 
> `/userdata/system/configs/emulationstation/es_systems.cfg`. Be careful
> if doing this, as the entire notion of maintaining this file as
> Batocera upgrades its internals (namely Python) thus rely on you. This
> is really only suitable if you never intend on updating Batocera
> again.

> Whenever Batocera is upgraded, its version of Python used may also
> change. This means if you are using an  `es_systems.cfg`  which
> manually defines the  `<command>`  (for example: 
> `<command>/usr/lib/python2.7/site-packages/configgen/emulatorlauncher.py</command>`
> which is calling an older Python version), it will need to be updated
> accordingly.
> 
> In general, it is recommended to avoid using a custom  `<command>` 
> and to just use the default one.

## Modify an existing system with a new system-specific "es_systems_<custom_name>.cfg" file[](https://wiki.batocera.org/emulationstation:customize_systems#modify_an_existing_system_with_a_new_system-specific_es_systems_custom_name_cfg_file)

You can create a file named  `es_systems_<custom_name>.cfg`  where  `<custom_name>`  is a name you wish to use for it. This file needs to follow the same conventions as the original  `es_systems.cfg`, but does not need to include the entirety of the file. For example:

[es_systems_3do.cfg](https://wiki.batocera.org/_export/code/emulationstation:customize_systems?codeblock=0 "Download Snippet")

    <?xml version="1.0"?>
    <systemList>
      <!-- This line is a comment, not necessary for the system. These will explain things, and can be safely removed. -->
      <system>
            <!-- The full name of the system, the one that will appear in menus and such. -->
            <fullname>3DO Interactive Multiplayer</fullname>
            <!-- The short name, the one used for the path to the system's ROMs and other internal uses. -->
            <name>3do</name>
            <!-- Metadata. The company/companies that made the system, also known as "Brand". Metadata tags like this aren't truly necessary, but can make organization easier. -->
            <manufacturer>Panasonic - Sanyo - Goldstar</manufacturer>
            <!-- Metadata. Release date. -->
            <release>1993</release>
            <!-- The type of hardware. Batocera doesn't particularly use this for anything, but it might be useful to specify here for future changes. -->
            <hardware>console</hardware>
            <!-- Extremely important, the path to look for this system's ROMs in. This should always start with /userdata/roms/. -->
            <path>/userdata/roms/3do</path>
            <!-- The file extensions of ROMs that should be scanned into ES's gamelist.xml when the user rescans their gamelist. Delimited by whitespaces. You must include the period mark (.) and proper capitalization. -->
            <extension>.iso .chd .cue</extension>
            <!-- Ordinarily this is the command line used to directly run the program, but Batocera relies on config generators to do so. This simply calls that generator, along with some other information. -->
            <command>python /usr/lib/python3.9/site-packages/configgen/emulatorlauncher.py %CONTROLLERSCONFIG% -system %SYSTEM% -rom %ROM%</command>
            <!-- The platform to use when scraping for metadata for this system's games. The full list of available platforms are in https://github.com/batocera-linux/batocera-emulationstation/blob/master/es-app/src/PlatformId.cpp -->
            <platform>3do</platform>
            <!-- The theme to load from the current theme-set, if supported. Usually, this is identical to the shortname. Check your theme's readme for more info. -->
            <theme>3do</theme>
            <emulators>
            <!-- These are the emulators used for the system. This is handled entirely by Batocera, and is not necessary for a custom es systems, but is shown here for reference. -->
                <emulator name="libretro">
                    <cores>
                        <core default="true">opera</core>
                    </cores>
                </emulator>
            </emulators>
      </system>
    </systemList>

would only affect the 3DO system on your Batocera, with the rest of the systems still referring to  `/usr/share/emulationstation/es_systems.cfg`  for their system CFG. When both files contain the same  `<name>`,  `es_systems_<custom_name>.cfg`  will take priority.

In case you'd like to have complete control over ES systems CFG, you can still use the two previous methods to completely override it (ie. using overlays or copying the entirety of  `es_systems.cfg`  to  `/userdata/system/configs/emulationstation/es_systems.cfg`  without appending a custom system name to its filename).

Batocera is smart enough to  _only_  apply the changes you make. Such as, if the only thing you need to change for a system is its ROM path, you can use the following in your  `/userdata/system/configs/emulationstation/es_systems_pico8.cfg`:

[es_systems_pico8.cfg](https://wiki.batocera.org/_export/code/emulationstation:customize_systems?codeblock=1 "Download Snippet")

    <?xml version="1.0" encoding="UTF-8"?>
    <systemList>
      <system>
            <name>pico8</name>        
            <path>/userdata/roms/pico8real</path>
      </system>
    </systemList>

Here, it'll use the folder  `/userdata/roms/pico8real/`  to look for Pico-8 games instead of the regular one, and use the rest of the configuration from the  `/usr/share/emulationstation/es_systems.cfg`  file.

## Create a new system[](https://wiki.batocera.org/emulationstation:customize_systems#create_a_new_system)

The method above can also be applied to make a brand new system in place of editing an already existing one. For instance, you might want to create a new “megadrivehacks” system intended for Megadrive/Genesis ROMhacks.

Create a  `/userdata/system/configs/emulationstation/es_systems_megadrivehacks.cfg`  file that contains the following:

[es_systems_megadrivehacks.cfg](https://wiki.batocera.org/_export/code/emulationstation:customize_systems?codeblock=2 "Download Snippet")

    <?xml version="1.0"?>
    <systemList>
      <system>
            <!-- The custom name of this system. -->
            <fullname>Megadrive hacks</fullname>
            <!-- Keep the name the same for the system you are basing it off it, saving you work later. -->
            <name>megadrive</name>
            <manufacturer>Sega</manufacturer>
            <release>1988</release>
            <hardware>console</hardware>
            <!-- Specify your new path. -->
            <path>/userdata/roms/megadrivehacks</path>
            <extension>.bin .gen .md .sg .smd .zip .7z</extension>
            <command>python /usr/lib/python3.9/site-packages/configgen/emulatorlauncher.py %CONTROLLERSCONFIG% -system %SYSTEM% -rom %ROM%</command>
            <!-- Since this is used only for scraping, it's safe to leave it as default. You'll probably have to be providing your own metadata for ROMhacks anyway. -->
            <platform>megadrive</platform>
            <!-- Change the theme to use the custom assets instead. -->
            <theme>megadrivehacks</theme>
            <!-- Leave the emulators the same. -->
            <emulators>
                <emulator name="libretro">
                    <cores>
                        <core>blastem</core>
                        <core default="true">genesisplusgx</core>
                        <core>genesisplusgx-wide</core>
                        <core>picodrive</core>
                    </cores>
                </emulator>
            </emulators>
      </system>
    </systemList>

The  `<name>`  and  `<platform>`  paths in this example are kept the same such that they can still use the defaults as specified by Batocera. If you really want to use a unique  `<name>`, you'll have to manually specify your default emulator in  `batocera.conf`. For instance if you were defining a new system with  `<name>cps1</name>`  then the following would be added to  `batocera.conf`:

    cps1.emulator=libretro
    cps1.core=fbneo

These default emulators can also be defined in the  `/usr/share/batocera/configgen/configgen-defaults.yml`  and/or  `/usr/share/batocera/configgen/configgen-defaults-arch.yml`  system defaults file.

> You must use a unique  `<name>`  field when adding a new system if you
> wish to keep the old one in addition. However, if using duplicate
> shortnames is a necessity and you still want the new and old system to
> exist simultaneously, you can also put both systems in a single CFG
> file.

> Despite  `<core default=“true”>`  being specified in the 
> `es_systems_megadrivehacks.cfg`  file, Batocera doesn't actually use
> this as the default when launching an emulator. It instead looks for
> its own list of defaults for its configgen.

In case you're making a brand new system with brand new emulators/parameters, refer to  [the developer documentation](https://wiki.batocera.org/coding_rules#how_to_add_an_emulator "coding_rules")  instead.