问题
The emulator is running. But when I write adb shell in my shell I get:
error:device offline
What is the reason for this? How do I get rid of it?
回答1:
If "adb devices" lists your device but as "offline" chances are your path leads to an old version of adb (eg 1.0.29) which has problems with latest Android 4 devices. Make sure "adb version" returns 1.0.31 or greater. Starting with Android 4.2.2, you must confirm on your device that it is being attached to a trusted computer. It will work with adb version 1.0.31 and above.
回答2:
It happened to me once. I just rebooted the device, and this solved the problem for me.
回答3:
When I got that same error, I just unplugged and plugged in it and the error disappeared.
回答4:
I restarted my computer, and at the same time I rebooted the phone. The adb devices returns fine.
回答5:
If you are connecting through USB, unplug and plug it in again.
If you are connecting over WiFi, disable and re-enable WiFi on the phone.
回答6:
If you are on Linux or Mac, and assuming the offline device is 'emulator-5554', you can run the following:
netstat -tulpn|grep 5554
Which yields the following output:
tcp 0 0 127.0.0.1:5554 0.0.0.0:* LISTEN 4848/emulator64-x86
tcp 0 0 127.0.0.1:5555 0.0.0.0:* LISTEN 4848/emulator64-x86
This tells me that the process id 4848 is still listening on port 5554. You can now kill that process with:
sudo kill -9 4848
and the ghost offline-device is no more!
回答7:
Try to run:
adb kill-server
adb start-server
Still device offline, please restart device.
回答8:
Make sure you're superuser.. Instead of 'adb start-server' do 'sudo adb start-server', enter your password (it will not echo), press enter. Then, 'sudo adb devices' and it will show as online.
回答9:
I came with this condition twice.The first time I used the command "adb kill-server" in my PC, and restarted the android device. It worked. However the second time the method didn't work any more.This time I disconnected and reconnected the network. It worked.
回答10:
Method 1 :
run this commands in your linux terminal
sudo adb kill-server
sudo adb devices
run this commands in your CMD
adb kill-server
adb devices
"adb devices" result must show any device with id. If instead of id you are getting off-line means you need to give permission in your tab. Once you enable USB Debugging in android and connect the device for the first time you will get an alert dialog for giving permission. If you are not getting any pop-up then click on Revoke USB Permission in Developer option the try once.
Method 2:
Change the device connected mode from Media to Camera, sometimes this helped me.
Method 3 :
Update the adb as well as device drivers.
回答11:
This happened to me running Ubuntu 19.04 and Android 9. I fixed this by turning off developer options then turning it back on. And make sure USB Debugging is allowed in there as well.
回答12:
Install this tool (link) and try the following code, do not forget to have the device connected and be attentive to any message.
cd .... platform-tools/
adb kill-server
adb start-server
来源：https://stackoverflow.com/questions/10680417/error-device-offline