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adb devices: list phones and fix unauthorized or missing ones ​

In short: adb devices lists the Android phones and emulators that adb can see, with each one's serial number and state. device means ready, unauthorized means the phone is waiting for you to tap Allow on its USB debugging prompt, and offline means it is not answering. adb devices -l adds the model, and adb kill-server fixes many missing phones.

adb devices is the first command to run when anything else fails, because it tells you whether adb can reach the phone at all.

Syntax and output ​

bash
adb devices      # serial number and state
adb devices -l   # adds the USB port, product, model and transport ID
text
List of devices attached
R58M12345            device usb:1-2 product:a54xeea model:SM_A546B device:a54x transport_id:3
192.168.1.20:41037   device product:panther model:Pixel_7 device:panther transport_id:4
emulator-5554        unauthorized

A phone connected over Wi-Fi shows its IP address and port as its serial number; emulators show emulator- and a port.

StateWhat it means
deviceConnected and ready for commands
unauthorizedConnected, but the phone has not allowed this computer: tap Allow on the phone
offlineadb can see it but it is not answering
no permissionsLinux only: your user may not open the USB device
recovery or sideloadThe phone is in recovery mode, not in Android

Fix an unauthorized phone ​

  1. Unlock the phone and look for Allow USB debugging?; tick Always allow from this computer and tap Allow.
  2. No prompt? In Developer options, tap Revoke USB debugging authorisations, unplug the phone and plug it in again.
  3. Run adb kill-server, then adb devices, and watch the phone for the prompt.

The computer's key lives in the .android folder in your home folder; a new key means every phone asks again.

Fix a phone that is not listed ​

  • The cable. Many cables only charge. Try one you know carries data, and a port on the computer rather than a hub.
  • Developer options. Check that USB debugging is still on; some phones turn it off after an update.
  • The USB mode. If the phone asks what the connection is for, choose File transfer.
  • Drivers on Windows. Some phones need their maker's USB driver before adb can see them.
  • Linux permissions. A no permissions state means your user needs a udev rule for the phone.
  • Wi-Fi. A phone on Wi-Fi only appears after adb connect; see ADB over Wi-Fi.
  • The server. Restart it:
bash
adb kill-server && adb start-server && adb devices
powershell
adb kill-server; adb start-server; adb devices

Fix an offline phone ​

Unplug the phone and plug it in again, then restart the ADB server. If it keeps happening, update Platform-Tools: an old adb can show newer phones as offline. Restarting the phone helps when nothing else does.

On many phones at once ​

With several phones, adb devices is your inventory. Count the ready ones and list the rest:

bash
adb devices | awk 'NR>1 && NF {print $2}' | sort | uniq -c
powershell
adb devices | Select-Object -Skip 1 | Where-Object { $_ } | ForEach-Object { ($_ -split '\s+')[1] } | Group-Object | Select-Object Count, Name

Large labs put the phones on powered USB hubs, because a computer's own ports seldom supply enough power for many phones at once. BenchFleet shows every connected phone on one screen, with each phone's connection, battery, temperature and storage on its tile and problems shown in red.

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Common errors and fixes ​

ErrorWhat it meansFix
no devices/emulators foundadb sees no phoneWork through the list above, starting with the cable
device unauthorizedThe phone has not allowed this computerTap Allow on the phone; revoke and retry if there is no prompt
device offlineThe phone stopped answeringReconnect it and restart the ADB server
adb server version doesn't match this clientTwo different copies of adb are installed, for example one from another toolUse one copy of Platform-Tools, and close tools that bring their own adb
cannot bind to 127.0.0.1:5037Another program is already using the ADB server's portClose the other tool's adb, or restart the computer

Questions ​

Why does adb say my device is unauthorized?

The phone has not allowed this computer yet. Unlock it and tap Allow on the Allow USB debugging prompt, ticking Always allow from this computer. If no prompt appears, revoke USB debugging authorisations in Developer options, plug the phone in again and run adb kill-server.

Why does adb devices show nothing?

Most often the cable only charges, USB debugging is off, or Windows lacks the phone's USB driver. Try a cable you know carries data, check Developer options, choose File transfer when the phone asks what the USB connection is for, and restart the ADB server.

What does offline mean in adb devices?

adb can see the phone but it is not answering, often after sleep, a reconnect or with an old version of adb. Unplug and reconnect it, restart the ADB server, and update Platform-Tools if the problem keeps coming back.

How do I restart the ADB server?

Run adb kill-server; the next adb command, such as adb devices, starts a new server. adb start-server starts it straight away. Every phone disconnects for a moment.

How many phones can adb see at once?

In practice your USB ports, powered hubs, power supply and network set the limit rather than adb. Every phone appears in adb devices with its own serial number, and you choose one with -s.

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