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Android Development
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Runtime Images: User Data and SD Card

At runtime, the emulator reads and writes data on two disk images: a user-data image and (optionally) an SD card image. This emulates the user-data partition and removable storage media on actual device.

The emulator provides a default user-data disk image. At startup, the emulator creates the default image as a copy of the system user-data image (user-data.img), described above. The emulator stores the new image with the files of the active AVD.

The emulator provides startup options to let you override the actual names and storage locations of the runtime images to load, as described in the table below. When you use one of these options, the emulator looks for the specified file(s) in the current working directory, in the AVD directory, or in a custom location (if you specified a path with the filename).

Name Description Comments
userdata-qemu.img An image to which the emulator writes runtime user-data for a unique user. Override using -data <filepath>, where <filepath> is the path the image, relative to the current working directory. If you supply a filename only, the emulator looks for the file in the current working directory. If the file at <filepath> does not exist, the emulator creates an image from the default userdata.img, stores it under the name you specified, and persists user data to it at shutdown.
sdcard.img An image representing an SD card inserted into the emulated device. Override using -sdcard <filepath>, where <filepath> is the path the image, relative to the current working directory. If you supply a filename only, the emulator looks for the file in the current working directory.

User-Data Image

Each emulator instance uses a writeable user-data image to store user- and session-specific data. For example, it uses the image to store a unique user's installed application data, settings, databases, and files.

At startup, the emulator attempts to load a user-data image stored during a previous session. It looks for the file in the current working directory, in the AVD directory as described above, and at the custom location/name that you specified at startup.

  • If it finds a user-data image, it mounts the image and makes it available to the system for reading/writing of user data.
  • If it does not find one, it creates an image by copying the system user-data image (userdata.img), described above. At device power-off, the system persists the user data to the image, so that it will be available in the next session. Note that the emulator stores the new disk image at the location/name that you specify in -data startup option.

Note: Because of the AVD configurations used in the emulator, each emulator instance now gets its own dedicated storage. There is no need to use the -d option to specify an instance-specific storage area.

SD Card

Optionally, you can create a writeable disk image that the emulator can use to simulate removeable storage in an actual device. For information about how to create an emulated SD card and load it in the emulator, see SD Card Emulation

You can also use the android tool to automatically create an SD Card image for you, when creating an AVD. For more information, see Command-line options for AVDs.
Android Development
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