Isilon: How to get a node into single-user mode

Introduction

This article describes how to get a node into single user mode. Single-user mode starts the node with a limited environment. You are placed in a shell with the root file system mounted as read-only. This mode is useful for maintenance or when the node cannot be booted into multi-user mode. 

Procedure

Choose the appropriate instructions based on whether the node is running in multi-user mode:

• If the node is in multi-user mode
• If the node is not in multi-user mode

If the node is in multi-user mode.

If the node is in multi-user mode (normal operating mode), or if you can bring the node up in multi-user mode,  Nextboot Command can be used to specify boot options and a kernel for the next boot. These settings are not preserved, and the boot sequence reverts to its prior configuration after the first reboot is complete.

1. Connect to the node using the management port 
2. Log in as root.
3. Run the following command from the command line to verify the directory of the running kernel:
    

   sysctl kern.bootfile

   
   
   
   Output similar to the following is displayed:
    

   kern.bootfile: /boot/kernel.amd64/kernel

   
   
   
   This indicates that the kernel boot directory is kernel.amd64.
    
4. Run the following command to enable booting into single-user mode, where <kernel_boot_dir> is the directory obtained from the output in step 3. In the example in step 1, <kernel_boot_dir> is kernel.amd64:
    

   nextboot -o "-s" -k <kernel_boot_dir>

   
   
    

   NOTE
   If you must remove an existing nextboot configuration, run the following command before rebooting the node:
    

   nextboot -D

5. Reboot the node:
    

   reboot

   
   
   
   The node then partially boots, and then displays the following message:
    

   Enter full pathname of shell or RETURN for /bin/sh:

   
   
    
6. Press ENTER.
   You are now at a single-user-mode command prompt. The root partition is mounted as read-only.
7. Mount the root partition as read/write
8. To return the node to multi-user mode, issue the Reboot Command

If the node is not in multi-user mode.

If it is not possible or desirable to start the node in multi-user mode, follow these steps: (for instance, if the node is unresponsive when attempting to boot in multi-user mode, or the node is powered off),

1. Connect to the node using the management port 
2. If the node stops responding, power off the node, wait 15 s, and power it back on.
3. If the node is powered off, press the power switch on the back panel to restart the node.
4. When you see the following line during the boot sequence, press the Spacebar.
    

   Hit [Enter] to boot immediately, or any other key for command prompt.

   
   
    

   NOTE
   Make sure that you press the Spacebar and not ENTER. Pressing the Spacebar multiple times ensures it is recognized on the system.

5. At the OK Prompt, run the following command:
    

   boot -s

   
   
   
   The system displays a message similar to the following:
    

   /boot/kernel/acpi.ko text=0x35a08 data=0x1630+0x6f4 syms=[0x4+0x4e30+0x4+0x6719]
   Mounting root from ufs:/dev/imdd0a
   Enter full pathname of shell or RETURN for /bin/sh:

6. Press Enter.
   
   You are now at a single-user-mode command prompt. The root partition is mounted as read-only.
    
7. Mount the root partition as read/write,