adb is running normally.

 Performing com.xxx.xxx activity launch

 Automatic Target Mode: using device 'XXXX'

 Uploading XXX.apk onto device 'XXXX'

 Installing XXX.apk...

 Application already exists. Attempting to re-install instead...

 Re-installation failed due to different application signatures.

 You must perform a full uninstall of the application. WARNING: This will remove the application data!

 Please execute 'adb uninstall com.xxx.xxx' in a shell.

 Launch canceled!

这样的问题主要是签名冲突造成的，比如你使用了ADB的debug权限签名，但后来使用标准sign签名后再安装同一个文件会出现这样的错误提示，解决的方法除了只有先从手机上卸载原有版本再进行安装，而adb install -r参数也无法解决这个问题。