Android Debug Bridge (adb) is a versatile command line tool that lets you communicate with an emulator instance or connected Android-powered device. It is a client-server program that includes three components:

• A client, which runs on your development machine. You can invoke a client from a shell by issuing an adb command. Other Android tools such as the ADT plugin and DDMS also create adb clients.

• A server, which runs as a background process on your development machine. The server manages communication between the client and the adb daemon running on an emulator or device.

• A daemon, which runs as a background process on each emulator or device instance.

You can find the adb tool in <sdk>/platform-tools/.

The server then sets up connections to all running emulator/device instances. It locates emulator/device instances by scanning odd-numbered ports in the range 5555 to 5585, the range used by emulators/devices. Where the server finds an adb daemon, it sets up a connection to that port. Note that each emulator/device instance acquires a pair of sequential ports — an even-numbered port for console connections and an odd-numbered port for adb connections.

• Similar to many commands,when you don't know what can the usb do,you can import:

 $adb help

• Then you will see some introductions

device commands:
  adb push <local> <remote>    - copy file/dir to device
  adb pull <remote> [<local>]  - copy file/dir from device
  adb sync [ <directory> ]     - copy host->device only if changed
                                 (-l means list but don't copy)
                                 (see 'adb help all')
  adb shell                    - run remote shell interactively
  adb shell <command>          - run remote shell command
  adb emu <command>            - run emulator console command
  adb logcat [ <filter-spec> ] - View device log
  adb forward <local> <remote> - forward socket connections
                                 forward specs are one of:
                                   tcp:<port>
                                   localabstract:<unix domain socket name>
                                   localreserved:<unix domain socket name>
                                   localfilesystem:<unix domain socket name>
                                   dev:<character device name>
                                   jdwp:<process pid> (remote only)

• You can specify the target instance for a command using its adb-assigned serial number. You can use the devices command to obtain the serial numbers of running emulator/device instances. For example:

 $adb -s emulator-5556 install helloWorld.apk

Note:if you issue a command without specifying a target emulator/device instance while multiple devices are available, adb generates an error.

You can use adb to copy an application from your development computer and install it on an emulator/device instance. To do so, use the install command. With the command, you must specify the path to the .apk file that you want to install:

 $adb install <path_to_apk>

And then uninstall it:

 $adb uninstall <path_to_apk>

• if you are using the Eclipse IDE and have the ADT plugin installed, you do not need to use adb (or aapt) directly to install your application on the emulator/device. Instead, the ADT plugin handles the packaging and installation of the application for you.

You can use the adb commands pull and push to copy files to and from an emulator/device instance. Unlike the install command, which only copies an APK file to a specific location, the pull and push commands let you copy arbitrary directories and files to any location in an emulator/device instance.

• You can use this to copy file or directory from the emulator or device:

 $adb pull <remote> <local>

• You can use this to copy file or directory to the emulator or device:

 $adb push <remote> <local>

Note:In the commands, <local> and <remote> refer to the paths to the target files/directory on your development machine (local) and on the emulator/device instance (remote). For example:

 $adb push /work/tools/adb.txt /system

• You can use the shell command to issue commands, with or without entering the adb remote shell on the emulator/device.To issue a single command without entering a remote shell, use the shell command like this:

 $adb [-d|-e|-s <serialNumber>] shell <shell_command>

• Or enter a remote shell on an emulator/device like this:

 $adb [-d|-e|-s <serialNumber>] shell

• When you are ready to exit the remote shell, press CTRL+D or type exit.

The Android logging system provides a mechanism for collecting and viewing system debug output. Logs from various applications and portions of the system are collected in a series of circular buffers, which then can be viewed and filtered by the logcat command.

• You can use the logcat command to view and follow the contents of the system's log buffers. The general usage is:

[adb] logcat [option] ... [filter-spec] ...

• You can use the logcat command from your development computer or from a remote adb shell in an emulator/device instance. To view log output in your development computer, you use

 $adb logcat

• and from a remote adb shell you use

 $logcat

Some people will get such note when they use $adb device

List of devices attached
???????????? no permissions

• It is say that you don't have the permission to run ADB by USB.So you can set the USB permission.
• (1)find your USB ID:

$ lsusb
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 18d1:0003 Google Inc.
Bus 002 Device 002: ID 0461:4d81 Primax Electronics, Ltd
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 010: ID 0bb4:0c87 High Tech Computer Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Note: And then find your USB ID.Here I can find my USB ID is Bus 001 Device 003: ID 18d1:0003 Google Inc.

• (2)Add the rule

 $sudo vim /etc/udev/rules.d/70-android.rules

• (3)Add the message

 SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="0003",MODE="0666"

Note:The 18d1 and 0003 is my ID,you must add your ID.

• (4)Restart the service

 $sudo chmod a+rx /etc/udev/rules.d/70-android.rules
 $sudo service udev restart

• (5)Swap the USB cable and enter the directory where have the adb.

 $sudo ./adb kill-server
 $./adb devices
 $./adb root