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‎scenarios/FixFstabIssuesRepairVM/fix-fstab-issues-repair-vm.md

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---
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title: Troubleshoot Linux VM boot issues due to fstab errors | Microsoft Learn
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description: Explains why Linux VM cannot start and how to solve the problem.
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services: virtual-machines
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documentationcenter: ''
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author: divargas-msft
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ms.author: divargas
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manager: dcscontentpm
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tags: ''
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ms.custom: sap:My VM is not booting, linux-related-content, devx-track-azurecli, mode-api, innovation-engine
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ms.service: azure-virtual-machines
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ms.collection: linux
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ms.topic: troubleshooting
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ms.workload: infrastructure-services
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ms.tgt_pltfrm: vm-linux
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ms.devlang: azurecli
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ms.date: 02/25/2025
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---
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# Troubleshoot Linux VM boot issues due to fstab errors
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**Applies to:** :heavy_check_mark: Linux VMs
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<!-- Commenting out these entries as this information should be selected by the user along with the corresponding subscription and region
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The First step in this tutorial is to define environment variables, and install the corresponding package, if necessary.
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```azurecli-interactive
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export MY_RESOURCE_GROUP_NAME="myVMResourceGroup89f292"
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export MY_VM_NAME="myVM89f292"
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```
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-->
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The Linux filesystem table, fstab is a configuration table which is designed to configure rules where specific file systems are detected and mounted in an orderly manner during the system boot process.
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This article discusses multiple conditions where a wrong fstab configuration can lead to boot issue and provides troubleshooting guidance.
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Few common reasons that can lead to Virtual Machine Boot issues due to fstab misconfiguration are listed below:
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* Traditional filesystem name is used instead of the Universally Unique Identifier (UUID) of the filesystem.
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* An incorrect UUID is used.
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* An entry exists for an unattached device without `nofail` option within fstab configuration.
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* Incorrect entry within fstab configuration.
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## Identify fstab issues
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Check the current boot state of the VM in the serial log within the [Boot diagnostics] (/azure/virtual-machines/boot-diagnostics#boot-diagnostics-view) blade in the Azure portal. The VM will be in an Emergency Mode. You see log entries that resemble the following example leading to the Emergency Mode state:
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```output
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[K[[1;31m TIME [0m] Timed out waiting for device dev-incorrect.device.
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[[1;33mDEPEND[0m] Dependency failed for /data.
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[[1;33mDEPEND[0m] Dependency failed for Local File Systems.
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...
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Welcome to emergency mode! After logging in, type "journalctl -xb" to viewsystem logs, "systemctl reboot" to reboot, "systemctl default" to try again to boot into default mode.
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Give root password for maintenance
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(or type Control-D to continue)
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```
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>[!Note]
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> "/data" is an example of mount point used. Dependency failure for filesystem mount point will differ based on the names used.
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## Resolution
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There are 2 ways to resolve the issue:
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* Repair the VM online
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* [Use the Serial Console](#use-the-serial-console)
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* Repair the vm offline
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* [Use Azure Linux Auto Repair (ALAR)](#use-azure-linux-auto-repair-alar)
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* [Use Manual Method](#use-manual-method)
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#### Use Azure Linux Auto Repair (ALAR)
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Azure Linux Auto Repair (ALAR) scripts is a part of VM repair extension described in [Repair a Linux VM by using the Azure Virtual Machine repair commands](./repair-linux-vm-using-azure-virtual-machine-repair-commands.md). ALAR covers automation of multiple repair scenarios including `/etc/fstab` issues.
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The ALAR scripts use the repair extension `run` command and its `--run-id` option. The script-id for the automated recovery is: **linux-alar2**. Implement the following steps to automate fstab errors via offline ALAR approach:
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```azurecli-interactive
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output=$(az extension add -n vm-repair; az extension update -n vm-repair; az vm repair repair-button --button-command 'fstab' --verbose --resource-group $MY_RESOURCE_GROUP_NAME --name $MY_VM_NAME)
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value=$(echo "$output" | jq -r '.message')
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extracted=$(echo $value)
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echo "$extracted"
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```
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> [!NOTE]
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> The fstab repair script will take a backup of the original file and strip off any lines in the /etc/fstab file which are not needed to boot a system. After successful start of the OS, edit the fstab again and correct any errors which didn't allow a reboot of the system before.
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[!INCLUDE [Azure Help Support](../../../includes/azure-help-support.md)]

‎scenarios/KernelBootIssuesRepairVM/kernel-related-boot-issues-repairvm.md

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---
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title: Recover Azure Linux VM from kernel panic due to missing initramfs
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description: Provides solutions to an issue in which a Linux virtual machine (VM) can't boot after applying kernel changes.
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author: divargas-msft
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ms.author: divargas
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ms.date: 02/25/2025
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ms.reviewer: jofrance
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ms.service: azure-virtual-machines
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ms.custom: sap:Cannot start or stop my VM, devx-track-azurecli, mode-api, innovation-engine, linux-related-content
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ms.workload: infrastructure-services
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ms.tgt_pltfrm: vm-linux
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ms.collection: linux
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ms.topic: troubleshooting
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---
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# Azure Linux virtual machine fails to boot after applying kernel changes
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**Applies to:** :heavy_check_mark: Linux VMs
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<!-- Commenting out these entries as this information should be selected by the user along with the corresponding subscription and region
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The First step in this tutorial is to define environment variables, and install the corresponding package, if necessary.
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```azurecli-interactive
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export MY_RESOURCE_GROUP_NAME="myVMResourceGroup89f292"
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export MY_VM_NAME="myVM89f292"
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```
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-->
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## Prerequisites
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Make sure the [serial console](serial-console-linux.md) is enabled and functional in the Linux VM.
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## <a id="missing-initramfs"></a>Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
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This error occurs because of a recent system update (kernel). It's most commonly seen in RHEL-based distributions.
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You can [identify this issue from the Azure serial console](#identify-kernel-boot-issue). You'll see any of the following error messages:
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1. "Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)"
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```output
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[ 301.026129] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
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[ 301.027122] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G ------------ T 3.10.0-1160.36.2.el7.x86_64 #1
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[ 301.027122] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090008 12/07/2018
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[ 301.027122] Call Trace:
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[ 301.027122] [<ffffffff82383559>] dump_stack+0x19/0x1b
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[ 301.027122] [<ffffffff8237d261>] panic+0xe8/0x21f
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[ 301.027122] [<ffffffff8298b794>] mount_block_root+0x291/0x2a0
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[ 301.027122] [<ffffffff8298b7f6>] mount_root+0x53/0x56
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[ 301.027122] [<ffffffff8298b935>] prepare_namespace+0x13c/0x174
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[ 301.027122] [<ffffffff8298b412>] kernel_init_freeable+0x222/0x249
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[ 301.027122] [<ffffffff8298ab28>] ? initcall_blcklist+0xb0/0xb0
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[ 301.027122] [<ffffffff82372350>] ? rest_init+0x80/0x80
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[ 301.027122] [<ffffffff8237235e>] kernel_init+0xe/0x100
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[ 301.027122] [<ffffffff82395df7>] ret_from_fork_nospec_begin+0x21/0x21
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[ 301.027122] [<ffffffff82372350>] ? rest_init+0x80/0x80
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[ 301.027122] Kernel Offset: 0xc00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
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```
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2. "error: file '/initramfs-*.img' not found"
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> error: file '/initramfs-3.10.0-1160.36.2.el7.x86_64.img' not found.
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This kind of error indicates that the initramfs file isn't generated, the GRUB configuration file has the initrd entry missing after a patching process, or a GRUB manual misconfiguration.
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### <a id="missing-initramfs-alar"></a>Regenerate missing initramfs by using Azure Repair VM ALAR scripts
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1. Create a repair VM by running the following Bash command line with [Azure Cloud Shell](/azure/cloud-shell/overview). For more information, see [Use Azure Linux Auto Repair (ALAR) to fix a Linux VM - initrd option](repair-linux-vm-using-ALAR.md#initrd). This command will regenerate the initrd/initramfs image, regenerate the GRUB configuration file if it has the initrd entry missing, and swap the OS disk
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```azurecli-interactive
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output=$(az extension add -n vm-repair; az extension update -n vm-repair; az vm repair repair-button --button-command 'initrd' --verbose --resource-group $MY_RESOURCE_GROUP_NAME --name $MY_VM_NAME)
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value=$(echo "$output" | jq -r '.message')
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extracted=$(echo $value)
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echo "$extracted"
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```
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2. Once the repair VM command has been executed, restart the original VM and validate that it's able to boot up.
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## Next steps
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If the specific boot error isn't a kernel related boot issue, see [Troubleshoot Azure Linux Virtual Machines boot errors](./boot-error-troubleshoot-linux.md) for further troubleshooting options.
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[!INCLUDE [Azure Help Support](../../../includes/azure-help-support.md)]

‎scenarios/metadata.json

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"configurations": {
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"title": "Troubleshoot Linux VM boot issues due to fstab errors",
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"sourceUrl": "https://raw.githubusercontent.com/MicrosoftDocs/executable-docs/main/scenarios/FixFstabIssuesRepairVM/fix-fstab-issues-repair-vm.md",
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"documentationUrl": "https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/linux/linux-virtual-machine-cannot-start-fstab-errors#use-azure-linux-auto-repair-alar",
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"configurableParams": [
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{
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"commandKey": "MY_VM_NAME",
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"status": "active",
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"title": "Troubleshoot Linux VM boot issues due to fstab errors",
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"description": "Explains why Linux VM cannot start and how to solve the problem.",
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