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You can install LineageOS 15.1, based on Android 8.1 Oreo, on a compatible HTC One (M8), but in 2026 this is a legacy custom-ROM installation—not a current official update. The old official M8 installation guide remains available, but it does not provide a current 15.1 download. You will need a trustworthy archived ROM, a recovery and any optional Google Apps package that match your exact phone and ROM. Unlocking the bootloader and formatting data erase the phone, so back up first.
Before you begin: If you want the newest available Android build for the M8 rather than Oreo specifically, check the community-maintained M8 device page, which lists LineageOS 18.1 (Android 11). Its builds do not support Google Play Edition variants or devices using Google Play Edition firmware.
What to know before installing LineageOS 15.1
LineageOS 15.1 is an obsolete Android 8.1 release, not a maintained branch with current security updates. LineageOS says it generally does not retain builds after a device or version is deprecated, and archived packages may be unsigned, modified, incomplete, or unsupported. Read its policy on unsupported and archived builds before trusting an old package. Do not assume that a download described as “official” on a mirror is an authentic official release.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThis procedure replaces the phone’s operating system. It is not an incremental HTC software update: unlocking the bootloader wipes user data, and the clean-install process formats data again. Follow the instructions for the exact ROM package you obtain if they differ from the general legacy sequence below.
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- Display: 5.0-inches
- Camera: HTC UltraPixel
- Processor Speed: 2.3 GHz
- OS: Android 4.4.2 (KitKat)
- Unlocked cell phones are compatible with GSM carriers like AT&T and T-Mobile as well as with GSM SIM cards (e.g. H20, Straight Talk, and select prepaid carriers). Unlocked cell phones will not work with CDMA Carriers like Sprint, Verizon, Boost or Virgin.
Check that your phone is the right M8
The standard HTC One (M8) supported by the legacy guide uses the device codename m8. Similar names do not establish compatibility. Do not flash an M8 package onto an HTC One M8s, M8 Eye, E8, or another HTC model.
- On Android, check Settings > About for the model and hardware information.
- With the phone connected and USB debugging enabled, check from a computer with Platform-Tools:
adb shell getprop ro.product.deviceandadb shell getprop ro.product.model. The standard device codename should bem8. - Identify whether your phone is a carrier, regional, dual-SIM, or Google Play Edition model. Firmware and partition differences matter; the current community M8 page specifically excludes Google Play Edition variants and Google Play Edition firmware from its builds.
The current community device documentation describes the M8 as an ARM device with 2 GB of RAM and a Snapdragon 801 platform. That is why a compatible Google Apps package, if used, must be ARM rather than ARM64. See the M8 device information and the legacy M8 guide.
Gather the files and tools
On the computer
- Install Android SDK Platform-Tools, which include
adbandfastboot, from Google’s Platform-Tools page. - On Windows, install a suitable USB driver for the M8. Use a reliable data-capable USB cable.
- Download a recovery image explicitly intended for your M8 variant. TWRP’s HTC One M8 page identifies the device as
m8and gives a fastboot flashing method. Do not assume the newest recovery has been tested with every archived Oreo build; follow the ROM maintainer’s recovery recommendation where provided.
ROM and optional Google Apps
- Obtain the exact LineageOS 15.1 package for
m8from its original maintainer’s archived release page or a reputable device-development forum. No current official 15.1 M8 download is established here, so do not rely on a guessed filename or an arbitrary mirror. - Verify the package’s signature or checksum against information from the original publisher when available. Avoid link shorteners and packages with no verifiable provenance. If you cannot establish that the ROM is for your model and unaltered, do not flash it.
- Google Apps (GApps) are optional and are not included with LineageOS. If you need Google Play Services, choose a package matching Android 8.1, ARM architecture, and the ROM’s partition requirements. The legacy guide specifies ARM for the M8. The LineageOS GApps information explains that older-version packages may need to be sourced separately.
Back up and prepare the phone
Copy photos, videos, documents, and files from internal storage to another device. Back up contacts, messages, call history, authenticator or two-factor authentication data, and app-specific data such as WhatsApp using methods that you have verified. A phone backup may not restore perfectly across stock Android and LineageOS.
Keep the ROM and GApps ZIPs on a microSD card or on the computer for ADB sideload; formatting data deletes internal storage. Charge the phone and make sure you can access the files and any account credentials you will need after setup.
- On the phone, enable Developer options by tapping Build number repeatedly in the About settings.
- In Developer options, enable USB debugging and, if present, OEM unlocking.
- Connect the phone and run
adb devices. Accept the authorization prompt on the phone. Continue only when the device appears as authorized.
Unlock the bootloader
Unlocking erases the phone. HTCDev availability and supported-model behavior can change, and carrier variants may require a different community-supported method; check the current status before starting. The legacy M8 guide refers to the HTC bootloader portal.
- With USB debugging authorized, run
adb -d reboot bootloader. Alternatively, power off the phone, hold Volume Down + Power, and select FASTBOOT. - Confirm fastboot sees the phone by running
fastboot devices. Do not proceed if the command returns no device. - For the historical HTCDev route, obtain the identifier token with
fastboot oem get_identifier_token, then follow HTCDev’s current instructions for your model. Use only an unlock method known to apply to your exact variant. - Complete the on-device unlock confirmation. The phone resets and user data is erased. Set it up only far enough to re-enable Developer options and USB debugging before continuing.
Flash TWRP and boot directly into recovery
Place the recovery image in the same folder as fastboot and rename it twrp.img. TWRP’s M8 page uses this command:
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- 5.0-inch Full HD 1080p with 440ppi display
- Dual camera with UltraPixel
fastboot flash recovery twrp.imgAfter flashing, use the bootloader’s volume keys to select RECOVERY and confirm with Power. Boot directly into recovery rather than Android: some stock installations can replace a custom recovery on the next normal boot. Check that TWRP starts before wiping anything.
Format data, then install the ROM
In TWRP, use Wipe > Format Data and confirm. Return to the wipe menu, open Advanced Wipe, select Cache and System, then swipe to wipe. Formatting data removes encryption and deletes internal storage, so a ROM ZIP stored only there will be lost. The legacy M8 guide describes this clean-install sequence.
- In TWRP, select Advanced > ADB Sideload, then swipe to start sideload mode.
- On the computer, substitute the actual path and filename of the verified package:
adb -d sideload /path/to/your-verified-m8-lineage-15.1.zip. Do not copy that example filename as if it were a real release. - Wait for TWRP to report the installation result and inspect its log if needed. ADB may stop at about 47% or print
adb: failed to read command: Successeven when the sideload succeeded; judge by recovery’s result, not the percentage alone.
Install GApps before the first boot (optional)
If you want Google Play Services, remain in recovery after installing the ROM. Start Advanced > ADB Sideload again and send the matching Android 8.1 ARM package, using its real filename and path:
adb -d sideload /path/to/your-android-8.1-arm-gapps.zipInstall GApps immediately after the ROM and before booting into LineageOS. LineageOS warns that installing them after the first boot can cause crashes and generally requires a factory reset before reinstalling. If you do not need Google services, skip GApps and proceed with the ROM alone. See the LineageOS FAQ for the timing guidance.
Reboot and complete setup
After recovery reports successful installation of the ROM and, if selected, GApps, reboot the phone. The legacy M8 guide says first boot can take approximately 15 minutes; allow time for initial setup rather than interrupting the process immediately. If the boot animation continues substantially longer, return to recovery and use the troubleshooting steps below.
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Troubleshoot installation problems
adb devices or fastboot devices shows no phone
- Confirm the phone is in the intended mode: Android with USB debugging for ADB, or FASTBOOT for fastboot.
- Try another data-capable cable and USB port. The M8 guide warns that some fastboot connections hang; a USB 2.0 port or hub may help.
- On Windows, repair or install the device driver. On Linux, check USB permissions or the applicable udev rules.
- For ADB, unlock the phone and accept the debugging authorization prompt. Do not flash until fastboot detects the device.
Sideload appears to stop near 47%
That percentage alone does not prove failure. Check TWRP’s on-device result and installation log; the legacy M8 guide documents cases where the sideload succeeds despite the computer’s apparent error.
Recovery reports Error 7 or package verification failure
Stop rather than bypassing the check. Confirm the ROM is for m8 and the right variant, and check the recovery generation, firmware requirements, and migration instructions specified by that ROM’s maintainer. A wrong device package, incompatible firmware or bootloader, outdated recovery, or migration from an unofficial build without the required wipe can cause installation errors. The LineageOS FAQ lists these as common causes.
The phone bootloops after GApps or stays at the HTC logo
Return to recovery and inspect its log. Check that the ROM is for the correct model and that GApps, if used, is Android 8.1 ARM and was installed in the same recovery session before first boot. If the cause is unclear, back up anything still accessible, format data as required by the maintainer, then try the ROM without GApps to isolate the package. A phone stuck at the HTC logo may also have a failed recovery flash, incompatible firmware, incomplete installation, or failing storage. Verify the model and variant, restore the correct recovery through fastboot if possible, and consult the ROM maintainer’s recovery or RUU instructions. A repair may require carrier-specific firmware; not every soft brick has the same fix.
TWRP disappears after flashing
Boot directly into recovery immediately after flashing rather than booting Android first. TWRP notes that some devices can replace custom recovery during a normal boot.
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Missing Google apps are expected if you skipped GApps: LineageOS does not bundle proprietary Google applications. Push notifications generally require GApps or a correctly configured MicroG installation, according to the LineageOS FAQ.
Installing 15.1 over an existing LineageOS build
Do not treat every existing installation as an in-place update. A newer build on the same branch may sometimes install without a full data wipe, but a change of Android version must follow the target branch’s device-specific upgrade instructions. Moving from an unofficial build to an official one may require the guide’s full-wipe procedure. If you do not know the build’s origin or migration path, back up and treat it as a clean-install case rather than relying on the updater.
Do not relock the bootloader after installing. LineageOS warns that relocking can leave some devices unusable; see its FAQ.
Is Android 8.1 the right target in 2026?
Choose 15.1 only if you specifically need Oreo or have a reason to use this legacy release. An old Android version can lack current security fixes, and an unlocked bootloader or outdated system may cause banking, streaming, enterprise, or other apps to reject the phone. App compatibility, aging battery health, and worn internal storage can also limit usefulness. For a newer M8 option, the community device page lists LineageOS 18.1 based on Android 11, but its variant and firmware restrictions still apply; evaluate that build separately rather than treating it as a drop-in substitute.
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