Common ADB Problems and How to Fix Them

The three problems below cover most ADB failures on Windows, Mac, and Linux.

Quick diagnostics

Run these first before doing anything else:

# Check ADB version
adb version

# List connected devices
adb devices

# Check ADB server status
adb get-state

If adb devices returns an empty list or shows the device as unauthorized or offline, work through the problems below.

Problem 1: Device shows as “unauthorized”

$ adb devices
List of devices attached
ABC123456789    unauthorized

The computer’s RSA key was not authorized on the device. Common on first connection, or after USB debugging was toggled or developer options were reset.

Accept the RSA prompt

1. Disconnect and reconnect the USB cable.
2. Look for “Allow USB debugging?” on the device screen.
3. Check “Always allow from this computer” and tap “Allow”.

If the prompt never appears, continue.

Revoke and re-authorize

On the device: Settings, Developer Options, “Revoke USB debugging authorizations”. On the computer:

adb kill-server
adb start-server
adb devices

Check the device screen for the RSA prompt again.

Clear RSA keys manually

On Windows:

del %USERPROFILE%\.android\adbkey
del %USERPROFILE%\.android\adbkey.pub
adb kill-server
adb start-server

On Mac/Linux:

rm ~/.android/adbkey
rm ~/.android/adbkey.pub
adb kill-server
adb start-server

Reconnect the device and authorize the new prompt.

Problem 2: Device not detected

$ adb devices
List of devices attached
# (empty list)

Enable USB debugging

1. Settings, About phone, tap “Build number” 7 times for Developer Options.
2. Settings, Developer Options, enable “USB debugging” (and “USB debugging (Security settings)” if present).

Check the USB connection mode

Pull down the notification shade while connected, tap the USB notification, and select “File Transfer” (MTP) or PTP. “Charging only” mode will not work with ADB. Some devices behave better on PTP.

Try a different cable or port

• Use the cable that came with the phone, or one you know carries data.
• Connect directly to the computer – no USB hubs.
• Try different ports (USB 3.0 vs 2.0).

Warning: cheap charging-only cables lack data lines entirely and are a common cause of invisible devices.

Problem 3: Wireless ADB won’t connect

$ adb connect 192.168.1.100:5555
failed to connect to 192.168.1.100:5555

Android 11+: pair first, then connect

1. Settings, Developer Options, Wireless debugging – toggle ON.
2. Note the IP address and pairing port, e.g. 192.168.1.100:37847.
3. adb pair <IP>:<PAIR_PORT> with the code shown on the phone.
4. adb connect <IP>:<PORT> using the connection port from the Wireless debugging screen.

Android 10 and below: enable via USB first

# Connect device via USB first
adb tcpip 5555

# Find device IP
adb shell ip addr show wlan0

# Connect wirelessly
adb connect 192.168.1.100:5555

# Verify connection
adb devices

Summary

Problem	Quick fix
Unauthorized	Revoke authorizations, restart ADB, accept prompt
Not detected	Enable USB debugging, check cable/mode
Wireless won’t connect	Same network, pair first (11+), use USB to enable tcpip (older)
Version conflict	Remove duplicate ADB installations
Daemon not running	Kill ADB, check port 5037

When in doubt, restart everything: ADB server, the device, and if needed the computer.

Part of the series: The Complete ADB Guide — also in this series: What is ADB? · Install ADB · Essential Commands · Wireless ADB