Exploring the Android system: dumpsys command to obtain detailed information about system services

dumpsys is an executable file in the Android system. Its main function is to dump some information of the current Android system, such as Activity, package, etc. It is a very effective tool for analyzing Android device problems, viewing running status, usage, etc. It can obtain various system information and status, such as the PSS value of the process, and analyze the RAM usage of the process.

The syntax of dumpsys provides a flexible way to obtain and analyze information about various services in the Android system. The basic syntax structure is as follows:

 adb shell dumpsys [-t timeout] [--help | -l | --skipservices | service[arguments] | -c | -h]

• [-t timeout]: Optional parameter used to specify the timeout period (in seconds) for command execution. The default is 10 seconds.
• [--help | -l | --skipservices | service[arguments] | -c | -h]: Command-line options used to customize the output and behavior of dumpsys.

--help: Print instructions for using dumpsys.

-l: List all system services supported by dumpsys.

--skipservices: Specifies a list of services that do not need to be printed.

service[arguments]: Specifies the specific service to be queried and its optional parameters. By specifying the service name, you can get detailed information about a specific service.

-c: Output information in a machine-friendly format (usually key-value pairs), which may be useful for automated script parsing but may not be very friendly for human reading.

-h: Used after the specified service to print what parameters the service supports or how to use the service.

 % adb shell dumpsys -l Currently running services: DisplayFeatureControl DockObserver MiuiBackup MiuiCarService MiuiInit MiuiWifiService ProcessManager SchedBoostService SlaveWifiService SurfaceFlinger accessibility account activity activity_task adb

If dumpsys is run without any parameters, it will output detailed information about all system services. The output is very long. When solving specific problems, we usually only focus on the output of some specific system services. We only need to use the service name as a parameter of the dumpsys command to output only the information of a specific service. For example, if we want to output disk usage statistics, we can use the system service name diskstats as a parameter.

 % adb shell dumpsys diskstats Latency: 1ms [512B Data Write] Recent Disk Write Speed (kB/s) = 45546 Data-Free: 53243072K / 113006560K total = 47% free Cache-Free: 53243072K / 113006560K total = 47% free System-Free: 0K / 5192648K total = 0% free File-based Encryption: true App Size: 16656406016 App Data Size: 33915740160 App Cache Size: 2662189568 Photos Size: 77041664 Videos Size: 17559552 Audio Size: 38887424 Downloads Size: 0 System Size: 128000000000 Other Size: 9238536192

How it works

dumpsys is based on the service management and inter-process communication mechanism of the Android system. It obtains information about all registered services in the system by calling the ServiceManager service at the bottom of the Android system. ServiceManager is a core service in the Android system, responsible for managing all services in the system and providing a unified registration, discovery and communication mechanism.

When dumpsys is called, it interacts with the ServiceManager through the Binder inter-process communication (IPC) framework. Binder is a framework for inter-process communication provided by Android, allowing efficient communication and data exchange between different processes. Through Binder, dumpsys can request the ServiceManager to provide a list of all registered services in the current system, as well as detailed information about each service.

ServiceManager will respond to dumpsys's request and return the status information of all services in the system, including the service name, status, runtime statistics, etc. After receiving this information, dumpsys will parse and organize it and display it in a readable way.

 int main(int argc, char* const argv[]) { ... // 1. 首先获取servicemanager sp<IServiceManager> sm = defaultServiceManager(); ... // 2. 进行命令行参数解析bool showListOnly = false; if ((argc == 2) && (strcmp(argv[1], "-l") == 0)) { // 2.1 当参数仅为"-l" 时，设置只罗列出所有的服务名showListOnly = true; } if ((argc == 1) || showListOnly) { // 2.2 当不带任何参数时，则附加"-a" 参数，表示输出所有系统服务信息services = sm->listServices(); services.sort(sort_func); args.add(String16("-a")); } else { // 2.3 当带了一个参数时，表示仅输出指定的系统服务信息services.add(String16(argv[1])); for (int i=2; i<argc; i++) { args.add(String16(argv[i])); } } // 3. 罗列出services这个数组中的服务名称，到这一步为止，都还只是在dumpsys本身的逻辑中转悠const size_t N = services.size(); if (N > 1) { aout << "Currently running services:" << endl; for (size_t i=0; i<N; i++) { sp<IBinder> service = sm->checkService(services[i]); if (service != NULL) { aout << " " << services[i] << endl; } } } if (showListOnly) { return 0; } // 4. 输出services这个数组中所包含系统服务的详细信息for (size_t i=0; i<N; i++) { sp<IBinder> service = sm->checkService(services[i]); if (service != NULL) { ... // 4.1 调用service的dump方法，来输出service的具体信息int err = service->dump(STDOUT_FILENO, args); ... } ... } return 0; }

1. Get the servicemanager, all system services will be registered with the servicemanager
2. Parse command line parameters and set subsequent execution instruction sequences according to different parameters
3. Simply list the system service names that need to be output
4. Call the dump() method of a specific system service to output detailed information about the system service

Taking the above adb shell dumpsys diskstats command as an example, the dump() method is finally called to complete the output:

 protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) { // 1. 权限检查mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DUMP, TAG); // 2. 生成一个大小为512B的临时文件byte[] junk = new byte[512]; for (int i = 0; i < junk.length; i++) junk[i] = (byte) i; // Write nonzero bytes File tmp = new File(Environment.getDataDirectory(), "system/perftest.tmp"); // 3. 将512B的临时文件写入磁盘，目的是为了快速的测试写磁盘的延迟long before = SystemClock.uptimeMillis(); ... fos = new FileOutputStream(tmp); fos.write(junk); ... long after = SystemClock.uptimeMillis(); ... pw.print("Latency: "); pw.print(after - before); pw.println("ms [512B Data Write]"); ... // 4. 输出Data, Cache和System这几个分区的磁盘使用信息reportFreeSpace(Environment.getDataDirectory(), "Data", pw); reportFreeSpace(Environment.getDownloadCacheDirectory(), "Cache", pw); reportFreeSpace(new File("/system"), "System", pw); .... }