Update serial-console-grub-proactive-configuration.md

przlplx · web-flow · commit cb1e30d918b8 · 2025-08-22T12:22:06.000-07:00
Edit review per CI 7097
diff --git a/support/azure/virtual-machines/linux/serial-console-grub-proactive-configuration.md b/support/azure/virtual-machines/linux/serial-console-grub-proactive-configuration.md
@@ -24,67 +24,67 @@ You can improve the recovery times of your IaaS Linux virtual machine (VM) in mo
 You might have to perform a VM recovery for any of the following reasons:
 
 - Corrupted file system, kernel, or MBR (Master Boot Record)
+- Corrupted SSHD configurations files
 - Failed kernel upgrades
 - Incorrect GRUB kernel parameters
 - Incorrect fstab configuration
-- Firewall configuration
 - Lost password
-- Mangled sshd configurations files
+- Firewall configuration
 - Networking configuration
 
-Many other scenarios as detailed [here](./serial-console-linux.md#common-scenarios-for-accessing-the-serial-console).
+Many other scenarios are also possible, as detailed in the "Common scenarios for accessing the Serial Console" section of [Azure Serial Console for Linux](./serial-console-linux.md#common-scenarios-for-accessing-the-serial-console). Refer to this article for more help if you're a new user of the Serial Console.
 
 Verify that you can access GRUB and the Serial Console on your VMs that are deployed in Azure.
 
-If you're a new user of the Serial Console, refer to [this article](./serial-console-linux.md).
-
 > [!TIP]
 > Back up your files before you make changes.
 
 The following video demonstrates how you can quickly recover your Linux VM after you have access to GRUB.
 
 [Recover Linux VM Video](https://youtu.be/KevOc3d_SG4)
 
-There are several methods to improve recovery of Linux VMs. In a Cloud environment, this process has been challenging. We're continually updating our tooling and program features to improving the recovery time for services.
+## Recovery methods
+
+There are several methods to improve recovery of Linux VMs. In a Cloud environment, this process has been challenging. We're continually updating our tooling and program features to improve recovery time for services.
 
 By using the Azure Serial Console, you can interact with your Linux VM as if you were at a system's console. You can manipulate many configuration files and processes, including how the kernel starts up.
 
-The more experienced Linux or Unix sysstem admins will appreciate the **single user** and  **emergency** modes that are accessible through the Azure Serial Console. These features make Disk Swap and VM deletion operations redundant for many recovery scenarios.
+More experienced Linux or Unix system administrators can appreciate the Single User and Emergency modes that are accessible through the Azure Serial Console. These features make Disk Swap and VM deletion operations redundant for many recovery scenarios.
 
 The method of recovery depends on the problem that you experience. For example, a lost or misplaced password can be reset through Azure portal options by using **Reset Password**. The **Reset Password** feature is known as an *extension*. The feature communicates with the Linux Guest agent.
 
-Other extensions, such as Custom Script, are available. However, these options require that the Linux **waagent** is running and in a healthy state.
+Other extensions, such as Custom Script, are available. However, these options require that the Azure Linux VM Agent (waagent) is running and in a healthy state.
 
 :::image type="content" source="media/serial-console-grub-proactive-configuration/agent-status.png" alt-text="Screenshot of the Agent status in the Properties page in Azure portal.":::
 
 If you have access to the Azure Serial Console and GRUB, you can manage a password change or fix an incorrect configuration in minutes instead of hours. In the scenario in which your primary kernel becomes corrupted, you could even force the VM to start from an alternative kernel, if you have multiple kernels on the disk.
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/more-kernel.png" alt-text="Screenshot of the selected OS startup screen in GRUB showing multiple kernels that can be chosen.":::
+:::image type="content" source="media/serial-console-grub-proactive-configuration/more-kernel.png" alt-text="Screenshot of the selected OS startup screen in GRUB showing multiple kernels that you can choose.":::
 
-## Suggested order of recovery methods
+### Suggested order of recovery methods
 
 - Azure Serial Console
 
 - [Disk Swap](/azure/virtual-machines/windows/os-disk-swap)
 
 - Legacy Method
 
-## Disk swap video
+### Disk swap video
 
 If you don't have access to GRUB, watch [this video](https://youtu.be/m5t0GZ5oGAc) to see how you can easily automate the disk swap procedure to recover your VM.
 
-## Challenges
+## Configuration methods and challenges
 
 By default, not all Linux Azure VMs are configured for GRUB access or to be interrupted by the SysRq commands. Some older distros, such as LES 11, aren't configured to display a sign-in prompt in the Azure Serial Console. The following sections review various Linux distributions and discuss configurations that make GRUB available.
 
-## How to configure Linux VM to accept SysRq keys
+### How to configure Linux VM to accept SysRq keys
 
 By default, the SysRq key is enabled on some newer Linux distros. On other distros, it might be configured for accepting values only for certain SysRq functions.
 On older distros, it might be disabled completely.
 
-The SysRq feature is useful for rebooting a crashed or non-responding VM directly from the Azure Serial Console. It's also helpful to gain access to the GRUB menu. Aalternatively restarting a VM from another portal window or SSH session might drop your current console connection and end GRUB time-outs that used to display the GRUB menu.
+The SysRq feature is useful for restarting a non-responding VM directly from the Azure Serial Console. It's also helpful to gain access to the GRUB menu. Aalternatively, restarting a VM from another portal window or SSH session might drop your current console connection and end GRUB timeouts that previously displayed the GRUB menu.
 
-The VM must be configured to accept a value of **1** for the kernel parameter. This setting enables all functions of SysRq or 128, which enables restart and power off processes.
+The VM must be configured to accept a value of **1** for the kernel parameter. This setting enables all functions of SysRq or 128 for restart and power off processes.
 
 [Enable SysRq video](https://youtu.be/0doqFRrHz_Mc)
 
@@ -116,7 +116,7 @@ The system should log a reset message that resembles the message in the followin
 
 :::image type="content" source="media/serial-console-grub-proactive-configuration/retting-log.png" alt-text="Screenshot of the reset message log in the command-line interface.":::
 
-## Ubuntu GRUB configuration
+### Ubuntu GRUB configuration
 
 By default, you should be able to access GRUB by holding the **Esc** key during the VM restart. If the GRUB menu doesn't appear, you can force the GRUB menu to appear and stay on screen in the Azure Serial Console by using one of the following options.
 
@@ -144,7 +144,7 @@ Then, add the following line:
 GRUB_TIMEOUT_STYLE=countdown
 ```
 
-## Ubuntu 12\.04
+#### Ubuntu 12\.04
 
 Ubuntu 12.04 allows access to the serial console but doesn't offer the ability to interact. A **login:** prompt isn't displayed.
 
@@ -172,7 +172,7 @@ For Ubuntu 12.04 to obtain a **login:** prompt, follow these steps:
 
 For the required settings that you need to configure the serial console for Ubuntu versions, see the [SerialConsoleHowto](https://help.ubuntu.com/community/SerialConsoleHowto) Ubuntu documentation.
 
-## Ubuntu Recovery mode
+#### Ubuntu Recovery mode
 
 Additional recovery and clean-up options are available for Ubuntu through GRUB. However, these settings are accessible only if you configure kernel parameters accordingly.
 If you don't configure the kernel boot parameter, the Recovery menu is automatically sent to the Azure Diagnostics component and not to the Azure Serial Console. To get access to the Ubuntu Recovery menu, follow these steps:
@@ -205,9 +205,9 @@ If all goes well, the Recovery menu now displays additional options that can hel
 
 :::image type="content" source="media/serial-console-grub-proactive-configuration/additional-recovery-options-ubuntu.png" alt-text="Screenshot that shows the Serial console at the Recovery menu that offers additional recovery options.":::
 
-## Red Hat GRUB configuration
+### Red Hat GRUB configuration
 
-### Red Hat 7\.4\+ GRUB configuration
+#### Red Hat 7\.4\+ GRUB configuration
 
 The default /etc/default/grub configuration on these versions is adequately configured
 
@@ -222,15 +222,15 @@ GRUB_CMDLINE_LINUX="console=tty1 console=ttyS0 earlyprintk=ttyS0"
 GRUB_DISABLE_RECOVERY="true"
 ```
 
-Enable the SysRq key
+Enable the SysRq key:
 
 ```console
 sysctl -w kernel.sysrq=1;echo kernel.sysrq = 1 >> /etc/sysctl.conf;sysctl -a | grep -i sysrq
 ```
 
-### Red Hat 7\.2 and 7\.3 GRUB configuration
+#### Red Hat 7\.2 and 7\.3 GRUB configuration
 
-The file to modify is /etc/default/grub – a default config looks like this example:
+The file to modify is /etc/default/grub. The default configuration resembles the following example:
 
 ```console
 GRUB_TIMEOUT=1
@@ -242,31 +242,29 @@ GRUB_CMDLINE_LINUX="console=tty1 console=ttyS0 earlyprintk=ttyS0"
 GRUB_DISABLE_RECOVERY="true"
 ```
 
-Change the following lines in /etc/default/grub
+1. Locate the following (nonconsecutive) lines in /etc/default/grub:
 
 ```console
 GRUB_TIMEOUT=1 
 
-to
-
-GRUB_TIMEOUT=5
+GRUB_TERMINAL_OUTPUT="console"
 ```
 
-```console
-GRUB_TERMINAL_OUTPUT="console"
+Change these to the following:
 
-to
+```console
+GRUB_TIMEOUT=5
 
 GRUB_TERMINAL="serial console"
 ```
 
-Also add this line:
+Also, add this line:
 
 ```console
 GRUB_SERIAL_COMMAND="serial –speed=115200 –unit=0 –word=8 –parity=no –stop=1″
 ```
 
-/etc/default/grub should now look similar to this example:
+The example /etc/default/grub file should now appear as follows:
 
 ```console
 GRUB_TIMEOUT=5
@@ -278,24 +276,24 @@ GRUB_CMDLINE_LINUX="console=tty1 console=ttyS0 earlyprintk=ttyS0"
 GRUB_DISABLE_RECOVERY="true"
 ```
 
-Complete and update grub configuration using
+1. Complete and update the GRUB configuration by running the following command:
 
 `grub2-mkconfig -o /boot/grub2/grub.cfg`
 
-Set the SysRq kernel parameter:
+1. Set the SysRq kernel parameter:
 
 `sysctl -w kernel.sysrq = 1;echo kernel.sysrq = 1 >> /etc/sysctl.conf;sysctl -a | grep -i sysrq`
 
 Alternatively, you can configure GRUB and SysRq by using a single line, either in the shell or through the Run Command. Back up your files before you run this command:
 
 `cp /etc/default/grub /etc/default/grub.bak; sed -i 's/GRUB_TIMEOUT=1/GRUB_TIMEOUT=5/g' /etc/default/grub; sed -i 's/GRUB_TERMINAL_OUTPUT="console"/GRUB_TERMINAL="serial console"/g' /etc/default/grub; echo "GRUB_SERIAL_COMMAND=\"serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1\"" >> /etc/default/grub;grub2-mkconfig -o /boot/grub2/grub.cfg;sysctl -w kernel.sysrq=1;echo kernel.sysrq = 1 /etc/sysctl.conf;sysctl -a | grep -i sysrq`
 
-### Red Hat 6\.x GRUB configuration
+#### Red Hat 6\.*x* GRUB configuration
 
-The file to modify is /boot/grub/grub.conf. The `timeout` value will determine how long GRUB is shown for.
+The file to modify is /boot/grub/grub.conf. The `timeout` value will determine how long GRUB is dispplayed.
 
 ```console
-#boot=/dev/vda
+#boot=/dev/vda1
 default=0
 timeout=15
 splashimage=(hd0,0)/grub/splash.xpm.gz
@@ -305,53 +303,55 @@ terminal serial
 terminal --timeout=5 serial console
 ```
 
-The last line  *terminal –-timeout=5 serial console* will further increase **GRUB** timeout by adding a prompt of 5 seconds displaying **Press any key to continue.**
+The last line, *terminal –-timeout=5 serial console*, further increases the **GRUB** timeout value by adding a prompt of five seconds duration that displays the message, **Press any key to continue.**
+
+:::image type="content" source="media/serial-console-grub-proactive-configuration/press-any-key-to-continue.png" alt-text="Screenshot that shows console output.":::
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/press-any-key-to-continue.png" alt-text="Screenshot shows a console with output.":::
+The GRUB menu should appear on-screen for the configured value of **timeout=15** without having to press Esc. Select the console in the browser to make the menu active, and then select the required kernel.
 
-GRUB menu should appear on-screen for the configured timeout=15 without the need to press Esc. Make sure to click in the Console in the Browser to make active the menu and select the required kernel.
+:::image type="content" source="media/serial-console-grub-proactive-configuration/select-kernel.png" alt-text="Screenshot that shows a console that contains two Linux options.":::
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/select-kernel.png" alt-text="Screenshot shows a console with two Linux options.":::
+### SuSE GRUB configuration
 
-## SuSE
+#### SLES 12 SP1
 
-### SLES 12 sp1
+Use either of the following methods:
 
-Either use YaST bootloader as per the official [docs](./serial-console-grub-single-user-mode.md#grub-access-in-suse-sles)
+- Use the YaST bootloader per the steps in [Use Serial Console to access GRUB and single-user mode](./serial-console-grub-single-user-mode.md#general-single-user-mode-access).
 
-Or add/change to /etc/default/grub the following parameters:
+- Modify the /etc/default/grub file by specifying the following parameters:
 
 ```console
 GRUB_TERMINAL=serial
 GRUB_TIMEOUT=5
 GRUB_SERIAL_COMMAND="serial --unit=0 --speed=9600 --parity=no"
+```
 
-```console
-Verify that ttys0 is used in the GRUB_CMDLINE_LINUX or GRUB_CMDLINE_LINUX_DEFAULT
+Verify that `ttys0` is used in the GRUB_CMDLINE_LINUX or GRUB_CMDLINE_LINUX_DEFAULT command, as follows:
 
 ```console
 GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0,9600n"
 ```
 
-Recreate the grub.cfg
+Re-create the Grub.cfg file, as follows:
 
 `grub2-mkconfig -o /boot/grub2/grub.cfg`
 
-### SLES 11 SP4
+#### SLES 11 SP4
 
-The Serial Console appears and displays boot messages but doesn't display a **login:** prompt
+The Serial Console appears and displays startup messages but doesn't display a **login:** prompt. To resolve this problem, follow these steps:
 
-Open an ssh session into the VM and update the file **/etc/inittab** by un-commenting this line:
+1. Open an SSH session on the VM, and update the **/etc/inittab** file by uncommenting the following line:
 
 ```console
 #S0:12345:respawn:/sbin/agetty -L 9600 ttyS0 vt102
 ```
 
-Next run the command
+1. Run the following command:
 
 `telinit q`
 
-To enable GRUB, the following changes should be made to /boot/grub/menu.lst
+1. To enable GRUB, specify the following parameters in the /boot/grub/menu.lst file:
 
 ```console
 timeout 5
@@ -363,38 +363,39 @@ kernel /boot/vmlinuz-3.0.101-108.74-default root=/dev/disk/by-uuid/ab6b62bb--
 1a8c-45eb-96b1-1fbc535b9265 disk=/dev/sda  USE_BY_UUID_DEVICE_NAMES=1 earlyprinttk=ttyS0 console=ttyS0 showopts vga=0x314
 ```
 
- This configuration will enable the message **Press any key to continue** to appear on the console for 5 seconds
+This configuration triggers a prompt of five seconds duration on the console that displays the message, **Press any key to continue.**
+
+It then displays the GRUB menu for an additional five seconds. Press the down arrow to interrupt the counter, and then select a kernel that you want to start. You can make either of the following changes:
 
-It will then display the GRUB menu for an additional 5 seconds - by pressing the down arrow you will interrupt the counter and  select a kernel you want to boot either append the keyword **single** for single user mode that requires root password to be set.
+- Append the command **init=/bin/bash** to load the kernel and also make sure that the init program is replaced by a bash shell. In this manner, you gain access to a shell without having to enter a password. You can then update the password for Linux accounts or make other configuration changes.
 
-Appending the command **init=/bin/bash** will load the kernel but ensures that the init program is replaced by a bash shell.
+- Append the keyword **single** to force Single User mode. This mode requires that you set a root password.
 
-You will gain access to a shell without having to enter a password. You can then proceed to update password for Linux accounts or make other configuration changes.
+#### Force the kernel to a bash prompt
 
-## Force the kernel to a bash prompt
+Having access to GRUB allows you to interrupt the initialization process. This interaction is useful for many recovery procedures. If you don't have a root password (as required by Single User mode), you can start the kernel by replacing the init program with a bash prompt. 
 
-Having access to GRUB allows you to interrupt the initialization process this interaction is useful for many recovery procedures.
-If you don't have root password and single user requires you to have a root password, you can boot the kernel replacing the init program with a bash prompt – this interrupt can be achieved by appending init=/bin/bash to the kernel boot line
+1. To trigger the interruption, append `init=/bin/bash` to the kernel boot line.
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-kernel-boot.png" alt-text="Screenshot shows a console with the updated boot line.":::
+:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-kernel-boot.png" alt-text="Screenshot that shows a console that contains the updated boot line.":::
 
-Remount your / (root) file system RW using the command
+1. Remount your / (root) file system RW by running the following command:
 
 `mount -o remount,rw /`
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-remount.png" alt-text="Screenshot shows a console with a re-mount action.":::
+:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-remount.png" alt-text="Screenshot that shows a console that contains a remount action.":::
 
-Now you can perform a root password change or other Linux configuration change.
+1. Perform a root password change or other Linux configuration change.
 
-:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-change-password.png" alt-text="Screenshot shows a console where you can change root password and other configuration.":::
+:::image type="content" source="media/serial-console-grub-proactive-configuration/bash-change-password.png" alt-text="Screenshot that shows a console in which you can change the root password or make other configurations.":::
 
-Restart the VM by running the following command:
+1. Restart the VM by running the following command:
 
 `/sbin/reboot -f`
 
-## Single User mode
+#### Force Single User mode
 
-Alternatively, you might have to access the VM in Single User or Emergency mode. Select the kernel that you want to start or interrupt by using the arrow keys. Enter the desired mode by appending the keyword **single** or **1** to the kernel boot line. On RHEL systems, you can also append **rd.break**.
+You might have to access the VM in Single User or Emergency mode. Select the kernel that you want to start or interrupt by using the arrow keys. Enter the desired mode by appending the keyword **single** or **1** to the kernel boot line. On RHEL systems, you can also append **rd.break**.
 
 For more information about how to access Single User mode, see [Use Serial Console to access GRUB and single-user mode](./serial-console-grub-single-user-mode.md#general-single-user-mode-access)
 
