Always slim

A stock iOS simulator runs about 200 processes and holds 3–6 GB. Most of that is Apple services a React Native app never touches: Siri, Photos analysis, App Store, iCloud sync. Android images ship the same kind of background weight. simfleet's rule is simple: every device is slim unless someone explicitly asks for stock.

What slimming does

SimSlim disables background launchd services inside the simulator and reboots it so the change takes effect. A measured example on an iPad simulator: 146 of 170 managed services disabled, about 75 processes, about 630 MB resident.

simfleet sim boot applies the project's profile (simslimProfile in the config, if set) and returns only after simslim verify confirms it. A failed verification is retried once.

avdslim boots the emulator with -lowram, host GPU, and no audio or cameras, then disables around 45–50 background packages and records its state on the device.

simfleet boots with 2 GB guest RAM by default. Android 15 images swap heavily at avdslim's 1.5 GB default, which makes the device feel laggy. Change it with SIM_FLEET_ANDROID_RAM_MB or a --ram= entry in android.avdslimArgs.

Auto-slim

While simfleet serve runs, it checks every 15 seconds for devices that are booted but not slim — for example, ones started from Xcode, Android Studio, xcrun simctl boot, or another tool.

Platform	Behaviour
Android	Slimmed in place, no reboot. Typically takes about 5 seconds.
iOS, booted less than 4 minutes ago	Slimmed (this reboots it).
iOS, running longer	Reported as `needs-reboot` and shown as Unslimmed in the dashboard, with a Slim button. It is not rebooted automatically, because something may be mid-test on it.

status.autoSlim lists what the loop is doing:

{
  "enabled": true,
  "iosFreshBootSeconds": 240,
  "devices": [
    { "deviceId": "763B…", "platform": "ios", "status": "needs-reboot",
      "reason": "running unslimmed; slimming reboots it, so it is not interrupted automatically" }
  ]
}

Failed attempts back off for 10 minutes per device.

Stock devices

Sometimes you need the full platform, for example to reproduce a bug with Apple Pay or Google services. Ask for it explicitly:

simfleet sim boot <udid> --stock
simfleet emu boot <avd> --stock
simfleet sim restore <udid>        # restore a running simulator to stock
simfleet emu restore <avd>

Each of these records an opt-out that auto-slim respects. simfleet sim slim or emu slim clears it again.

Warning

Turn auto-slim off only if another tool must own device lifecycle: SIM_FLEET_AUTO_SLIM=0, or "autoSlim": false in .sim-fleet/project.json.