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Changing Parameters and Reconfiguring the System

After determining the parameter or parameters to adjust, you must change the parameters and you may need to reconfigure the system for the changes to take effect. The systune(1M) utility will tell you when you make parameter changes if you must reboot to activate those changes. There are several steps to reconfiguration procedure:

Backing Up the System

Before you reconfigure the system by changing kernel parameters, it's a good idea to have a current and complete backup of the system. See the IRIX Admin: Backup, Security, and Accounting guide.

Caution: Always back up the entire system before tuning.

Changing a Parameter

After determining the parameter you need to change (for example, you need to increase nproc because you have a large number of users) you must first back up the system and the kernel. Give the command:

cp /unix /unix.save
This command creates a safe copy of your kernel. Through the rest of this example, this is called your old saved kernel. If you make this copy, you can always go back to your old saved kernel if you are not satisfied with the results of your tuning.

Once your backups are complete, you can execute the systune(1M) command. Note that you can present new values to systune in either hexadecimal or decimal notation. Both values are printed by systune.

An invocation of systune(1M) to increase nproc looks something like this:

systune -i

Updates will be made to running system and /unix.install

systune-> nproc

        nproc = 400 (0x190)

systune-> nproc = 500

        nproc = 400 (0x190)

        Do you really want to change nproc to 500 (0x1f4)? (y/n) y

In order for the change in parameter nproc to become effective /unix.install must be moved to /unix and the system rebooted

systune-> quit
Then reboot your system. Also, be sure to document the parameter change you made in your system log book.

Caution: When you issue the reboot command, the system overwrites the current kernel (/unix) with the kernel you have just created (/unix.install). This is why you should always copy the current kernel to a safe place before rebooting.

Creating and Booting a New Kernel With autoconfig

The systune command creates a new kernel automatically. However, if you changed parameters without using systune, or if you have added new system hardware (such as a new CPU board on a multiprocessor system), you will need to use autoconfig to generate a new kernel.

The autoconfig command uses some environment variables. These variables are described in detail in the autoconfig(1M) reference page. If you have any of the following variables set, you may need to unset them before running autoconfig:

To build a new kernel after reconfiguring the system, follow these steps:

  1. Become the Superuser by giving the command:

    su

  2. Make a copy of your current kernel with the command:

    cp /unix /unix.save

  3. Give the command:

    /etc/autoconfig -f

    This command creates a new kernel and places it in the file /unix.install.

  4. Reboot your system with the command:

    reboot

Caution: When you issue the reboot command, the system overwrites the current kernel (/unix) with the kernel you have just created (/unix.install). This is why you should always copy the current kernel to a safe place before rebooting. An autoconfiguration script, found in /etc/rc2.d/S95autoconfig, runs during system start-up. This script asks you if you would like to build a new kernel under the following conditions:

If any of these conditions is true, the system prompts you during startup to reconfigure the operating system:

Automatically reconfigure the operating system? y

If you answer y to the prompt, the script runs lboot and generates /unix.install with the new image.You can disable the autoconfiguration script by renaming /etc/rc2.d/S95autoconfig to something else that does not begin with the letter S, for example, /etc/rc2.d/wasS95autoconfig.

Recovering from an Unbootable Kernel

The following procedure explains how to recover from an unbootable /unix, and describes how to get a viable version of the software running after an unsuccessful reconfiguration attempt. If you use the systune(1M) utility, you should never have to use this information, since systune will not allow you to set your parameters to unworkable values.

  1. If the system fails to reboot, try to reboot it a few more times. If it still fails, you need to interrupt the boot process and direct the boot PROM to boot from your old saved kernel (unix.save).

  2. Press the reset button.You will see the System Maintenance Menu:

    System Maintenance Menu

    1) Start System.

    2) Install System Software.

    3) Run Diagnostics.

    4) Recover System.

    5) Enter Command Monitor.

  3. Select option 5 to enter the Command Monitor. You see:

    Command Monitor. Type "exit" to return to the menu.

    >>

  4. Now at the >> prompt, tell the PROM to boot your old saved kernel. The command is:

    boot unix.save

    The system will then boot the old saved kernel.

  5. Once the system is running, use the following command to move your old saved kernel to the default /unix name. This method also keeps a copy of your old saved kernel in unix.save:

    cp /unix.save /unix

Then you can normally boot the system while you investigate the problem with the new kernel. Try to figure out what went wrong. What was changed that stopped the kernel from booting? Review the changes that you made.

The following appendices are provided:

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