The emulator needs several key image files to run appropriately.
Their exact location depends on whether you're using the emulator
from the Android SDK, or not (more details below).
The minimal required image files are the following:
kernel-qemu the emulator-specific Linux kernel image
ramdisk.img the ramdisk image used to boot the system
system.img the *initial* system image
userdata.img the *initial* data partition image
It will also use the following writable image files:
userdata-qemu.img the persistent data partition image
system-qemu.img an *optional* persistent system image
cache.img an *optional* cache partition image
sdcard.img an *optional* SD Card partition image
snapshots.img an *optional* state snapshots image
If you use a virtual device, its content directory should store
all writable images, and read-only ones will be found from the
corresponding platform/add-on directories. See -help-sdk-images
for more details.
If you are building from the Android build system, you should
have ANDROID_PRODUCT_OUT defined in your environment, and the
emulator shall be able to pick-up the right image files automatically.
See -help-build-images for more details.
If you're neither using the SDK or the Android build system, you
can still run the emulator by explicitely providing the paths to
*all* required disk images through a combination of the following
options: -sysdir, -datadir, -kernel, -ramdisk, -system, -data, -cache
-sdcard and -snapstorage.
The actual logic being that the emulator should be able to find all
images from the options you give it.
For more detail, see the corresponding -help-<option> entry.
Other related options are:
-init-data Specify an alternative *initial* user data image
-wipe-data Copy the content of the *initial* user data image
(userdata.img) into the writable one (userdata-qemu.img)
-no-cache do not use a cache partition, even if one is available.
-no-snapstorage do not use a state snapshot image, even if one is available.