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Working with Logs

Log files are especially helpful to developers, but not always very easy to access.

nimbus-cli uses adb logcat on Android, and on iOS it uses the Unix commands find and tail.

These logs are useful when examining the internal state of the app, or attaching to bug reports.


For iOS the logs that are displayed and captured are the app's logs. For Android, the logs are for the whole device. For Android devices also used for personal usage, you should probably not upload such logs anywhere.


Capturing a device log

nimbus-cli --app firefox_ios --channel developer \
capture-logs logs.txt


You can set up a different terminal window to watch the logs as they are generated.

nimbus-cli --app firefox_ios --channel developer tail-logs

If you know of any keywords you may be interested in, you can filter piping the output to the grep command.

For example, the following outputs any log entry containing the word send-tab.

nimbus-cli --app firefox_ios --channel developer tail-logs | grep -i send-tab

On iOS, because the reset-app command deletes the app contaner, the tail-logs command is only available after the first run after a reset, and stops after a reset.


This command is an analog for the experiments menu in the secret settings of Fenix and Firefox for iOS.

It relaunches the app, then asks the SDK to dump the state of the Nimbus SDK to the logs. For example:

For example, this is a section of logs captured on an Android device shortly after log-state, and an enrollment into the viewpoint-rolling-week-2-expansion-android experiment:

06-05 12:12:47.177 12737 12737 D nimbus::nimbus_client: nimbus_18d_NimbusClient_dump_state_to_log
06-05 12:12:47.177 12737 12737 I nimbus::nimbus_client: Slug | Features | Branch
06-05 12:12:47.177 12737 12737 I nimbus::nimbus_client: viewpoint-rolling-week-2-expansion-android | messaging | treatment
06-05 12:12:47.177 12737 12841 D nimbus::nimbus_client: nimbus_18d_NimbusClient_set_fetch_enabled

It is useful to use in conjunction with other logging commands:

nimbus-cli --app fenix --channel developer log-state
nimbus-cli --app fenix --channel developer tail-log | grep -i nimbus


nimbus-cli --app fenix --channel developer log-state
nimbus-cli --app fenix --channel developer capture-logs logs.txt

By default, log-state is called at the same time as the enroll command.


For iOS, it can be a bit tricky to see the state of logs at the beginning of a just-installed but not yet opened app.

You can do the same as enroll then tail-logs with by adding -- --console-pty {} to the end of the enroll command.

$ nimbus-cli --app firefox_ios --channel developer \
enroll \
ios-search-bar-placement-v2-treatment-a-rollout --branch treatment-a \
-- --console-pty {}

2023-06-15 17:06:29.611 💙 INFO [sync] Profile - [RUST][nimbus::nimbus_client] [Nimbus] Days since update: 0 2023-06-15 17:06:29.644 💙 INFO [sync] Profile - [RUST][nimbus::nimbus_client] Slug | Features | Branch 2023-06-15 17:06:29.645 💙 INFO [sync] Profile - [RUST][nimbus::nimbus_client] ios-search-bar-placement-v2-treatment-a-rollout | search | treatment-a 2023-06-15 17:06:29.645 💙 INFO [experiments] Experiments - Nimbus is ready!