Fstab (file system table) is a configuration file that is used to define how
disk partition, file system, and file share mounts in your Linux VM persist
across system reboots.
This document outlines multiple conditions where an incorrect fstab
configuration may result in a boot problem and offers troubleshooting
advice to fix the issue.
For other causes of boot failures, and to detect the cause automatically, see
[Troubleshoot Linux Compute Engine instance boot issues](https://docs.cloud.google.com/compute/docs/troubleshooting/troubleshooting-linux-boot-issues).
A few of the common issues with fstab misconfiguration are listed below:
- Syntax error in `fstab` configuration file
- An incorrect UUID
- An entry exists for an unattached/unavailable device
- Deprecated mount options like `nobarrier` for the xfs file system type in [SUSE](https://www.suse.com/c/xfs-nobarrier-option-is-now-more-than-deprecated) or [RHEL](https://access.redhat.com/solutions/5315771) images.
## Before you begin
- If you want to log serial port output in Cloud Logging, familiarize yourself with [Cloud Logging](https://docs.cloud.google.com/logging).
- If you haven't already, set up [authentication](https://docs.cloud.google.com/compute/docs/authentication). Authentication verifies your identity for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:
Select the tab for how you plan to use the samples on this page:
### Console
When you use the Google Cloud console to access Google Cloud services and
APIs, you don't need to set up authentication.
### gcloud
1.
[Install](https://docs.cloud.google.com/sdk/docs/install) the Google Cloud CLI.
After installation,
[initialize](https://docs.cloud.google.com/sdk/docs/initializing) the Google Cloud CLI by running the following command:
```bash
gcloud init
```
If you're using an external identity provider (IdP), you must first
[sign in to the gcloud CLI with your federated identity](https://docs.cloud.google.com/iam/docs/workforce-log-in-gcloud).
> [!NOTE]
> **Note:** If you installed the gcloud CLI previously, make sure you have the latest version by running `gcloud components update`.
2. [Set a default region and zone](https://docs.cloud.google.com/compute/docs/gcloud-compute#set_default_zone_and_region_in_your_local_client).
### REST
To use the REST API samples on this page in a local development environment, you use the
credentials you provide to the gcloud CLI.
1. [Install](https://docs.cloud.google.com/sdk/docs/install) the Google Cloud CLI.
2. If you're using an external identity provider (IdP), you must first [sign in to the gcloud CLI with your federated identity](https://docs.cloud.google.com/iam/docs/workforce-log-in-gcloud).
For more information, see
[Authenticate for using REST](https://docs.cloud.google.com/docs/authentication/rest)
in the Google Cloud authentication documentation.
## Identify fstab issues
For boot issues, Google highly recommends that you check the boot logs
in the Serial Console of the Linux VM. The VM goes into emergency mode
with an error message hinting that the issue is with fstab.
```
[K[[1;31m TIME [0m] Timed out waiting for device dev-incorrect.device.
[[1;33mDEPEND[0m] Dependency failed for /distribution.
[[1;33mDEPEND[0m] Dependency failed for Local File Systems.
...
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.
Give root password for maintenance
(or type Control-D to continue)
```
As per the error message, there is dependency failure for the `/distribution`
file system. The dependency failure for a file system mount point will differ
based on the file system names used.
## Resolution
Use the following options to solve the `fstab` error in Linux VMs hosted
in Google Cloud. You can resolve the issue faster using the serial console
than using the manual method.
> [!NOTE]
> **Note:** To fix the issue from emergency mode, you must have the root password. By default, a root password is not set on Google provided Linux images. If you didn't set a root password, use [Option 2](https://docs.cloud.google.com/compute/docs/troubleshooting/fstab-errors#option2) instead.
To use the following methods to resolve the fstab issue, you must
[enable serial port access for your VM](https://docs.cloud.google.com/compute/docs/troubleshooting/troubleshooting-using-serial-console#enable_instance_access).
### Option 1: Use the serial console to log into the VM in emergency mode
1. Log into the serial console of the VM from Google Cloud console.
2. In the current emergency mode, enter the root password to access your VM.
3. Use your favorite text editor to open the `fstab` file. Make the
necessary changes and save the changes to the `fstab` file. In the
following example, the `vi` editor is used.
```
vi /etc/fstab
```
In the previous example, the device for `/distribution` is detached from
the VM. Comment the line that references the file system or remove the
fstab entry for `/distribution` mount point.
Use `man fstab` for more
details about the fstab configuration and syntax.
4. Save the file and exit the editor. If you are using the `vi` editor, use
`ESC` + `:wq!` to save and exit the editor.
5. Resume the boot process by entering **reboot** at the prompt.
6. After successfully fixing the issue, the VM boot process should complete
and the login prompt appears in the serial console.
7. Verify you can log in to the VM again using SSH.
### Option 2 - Using Single User mode in Serial Console
This option can be used if the root password is not set.
Prerequisite: The `GRUB_TIMEOUT` parameter in the grub configuration file
must be set to a non-zero value. Usually this file is at
`/etc/default/grub`, but on some earlier distributions, it might be located
in a non-standard directory.
1. Go to the VM instances page in the Google Cloud console.
[Go to VM instances](https://console.cloud.google.com/compute/instances)
2. Log into the serial console of the Virtual Machine from the
Google Cloud console.
3. Click **RESET** for virtual machine from the Google Cloud console.
4. In the serial console window, interrupt the boot process by clicking the
arrow key to pause in the grub screen or menu.
5. In the list of kernels in the grub boot loader screen, choose the kernel
and press `e` on the keyboard.
6. Add the `rd.break` parameter at the end of the kernel line and press
`ctrl`+`x`. This helps in booting the VM into single user mode.
> [!NOTE]
> **Note:** The `rd.break` parameter works for RHEL, CENTOS, Oracle Linux, SUSE Operating Systems. This parameter isn't a persistent entry so no changes are required after boot. For Ubuntu 18.04, 20.04 and 22.04 LTS, you can add `systemd.unit=rescue.target` to boot into rescue mode which is similar to single user mode.
7. Mount the root file system in read write mode.
8. Analyze, make necessary change and save `fstab` file. Use `man fstab` for more
details about configuration and syntax. Use your favorite text editor to
open the `fstab` file. In the below example, the vi editor is used.
```
vi /etc/fstab
```
In this example, the device for `/distribution` is detached from the VM,
so comment the line or remove the fstab entry for the `/distribution`
mount point.
9. Save the file and exit from the editor. If you are using the vi editor, then use
`ESC` + `:wq!` to save and exit from fstab.
10. Resume the boot process by entering `reboot` at the prompt.
11. After successfully fixing the issue, the VM boot process should complete and
you should see the login prompt in the serial console.
12. Verify you can log in to the VM using SSH.
### Option 3 - Rescue the VM
This option can be used if the root password is not set or if you can't use
single user mode.
For more information, see
[Rescue an inaccessible VM](https://docs.cloud.google.com/compute/docs/troubleshooting/rescue-vm).