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This chapter is from the book

Building a Kernel

This section shows an example of taking an existing kernel running on an Integrity (Itanium) server and making some changes to it. Figure 5-1 shows some commonly performed kernel-related steps. I perform many of these steps in the following example.

Figure 5-1 Commonly Performed Kernel Configuration Steps

Normally, you should change the kernel configuration before making any changes to it. To save the configuration, use -s and place a comment with -C as shown in the following command:

# kconfig -C "Initial configuration of vPars/Oracle/Peoplesoft system" -s 
              Initial_vPars_Oracle_Peoplesoft
       * The current configuration has been saved to
         'Initial_vPars_Oracle_Peoplesoft'.
#

This command results in the following entry being made in /var/adm/kc.log:



======================================================================

Change to configuration 'Initial_vPars_Oracle_Peoplesoft'
at 09:38:45 EDT on 21 September 2004 by root:
Configuration saved from currently running configuration.

Initial configuration of vPars/Oracle/Peoplesoft system


This is the last entry in /var/adm/kc.log immediately after the kconfig command was issued. The -s option results in this kernel having been saved in the directory /stand/Initial_vPars_Oracle_Peoplesoft, as shown in the following long listing of /stand:

Initial configuration of vPars/Oracle/Peoplesoft system

# ll /stand
total 96976
drwxr-xr-x   5 root       sys   8192 Sep 21 09:38 Initial_vPars_Oracle_Peoplesoft
drwxr-xr-x   5 root       sys   8192 Sep 21 09:11 backup
dr-xr-xr-x   3 bin        bin     96 May  5 15:46 boot.sys
-rw-r--r--   1 root       sys     21 May  5 15:44 bootconf
lrwxr-xr-x   1 root       root    14 Sep 21 09:17 bootfs -> current/bootfs
drwxr-xr-x   5 root       root  8192 May 25 12:03 crashconfig
drwxr-xr-x   5 root       sys   8192 Sep 21 09:11 current
drwxr-xr-x   5 root       sys   8192 Sep 19 15:38 initial_11iv2
drwxr-xr-x   5 root       sys   8192 Sep 12 20:28 installed
-rw-r--r--   1 root       sys  16024 Sep 21 09:17 ioconfig
-r--r--r--   1 root       sys     82 May  5 16:11 kernrel
drwxr-xr-x   2 root       sys     96 Sep 21 09:21 krs
drwxr-xr-x   5 root       sys   8192 May  5 16:12 last_install
drwxr-xr-x   2 root       root    96 May  5 15:43 lost+found
lrwxr-xr-x   1 root       root     7 Sep 21 09:17 nextboot -> current
-rw-------   1 root       root    12 Sep 21 09:17 rootconf
lrwxr-xr-x   1 root       root    15 Sep 21 09:17 system -> nextboot/system
-r--r--r--   1 root       sys   1996 May  5 16:01 system.import
-rw-r--r--   1 root       sys   2537 May  5 16:51 system.prev
-rwxr-xr-x   5 root       other 4656 Jun 15 15:49 vmunix
#


This directory contains all files associated with the currently running kernel, as shown in the following long listing which are in the directory Initial_vPars_Oracle_Peoplesoft:


# ll
total 96784
-rw-r--r--   1 root       sys              0 Sep 21 09:38 .config
-rw-r--r--   1 root       sys            147 Sep 21 09:38 README
drwxr-xr-x   3 root       sys             96 Sep 21 09:38 bootfs
drwxr-xr-x   2 root       sys             96 Sep 21 09:38 krs
drwxr-xr-x   2 root       sys             96 Sep 21 09:38 mod
-rw-r--r--   1 root       sys           2877 Sep 21 09:38 system
-rwxr-xr-x   5 root       other     49534656 Jun 15 15:49 vmunix
#

This directory contains the currently running kernel vmunix, the current system file, and other files associated with the currently running kernel. You may also want to give each configuration a title using the -t option to kconfig.

At this point I am protected in that if I had to revert to the saved kernel configuration after making changes I can do so. Now that the current configuration has been saved I will view an existing tunable parameter and module that I plan to change with the following commands:

# kctune -d nproc
Tunable  Value  Expression  Changes
    Description
nproc     4200  Default     Immed
    Maximum number of processes on the system



# kcmodule -d idds
Module  State   Cause
    Description
idds    unused
    Intrusion Detection Data Source
#

I also issue kcusage on a system before making a change to see the level of usage. If the system is not in use, however, and you're preparing it for use, the usage will be low so the output is not meaningful.

In this example, I change nproc from 4200 to 8020 and change idds to best. Immediately before making these changes I add a comment to /var/adm/kc.log so that a record exists of why these changes were made:


# kctune -C "first of many tunable changes for vPars/Oracle/Peoplesoft config"    
  nproc=8020

WARNING: The automatic 'backup' configuration currently contains the
         configuration that was in use before the last reboot of this
         system.
     ==> Do you wish to update it to contain the current configuration
         before making the requested change? y
       * The automatic 'backup' configuration has been updated.
       * The requested changes have been applied to the currently
         running system.
Tunable            Value  Expression  Changes
nproc    (before)   4200  Default     Immed
         (now)      8020  8020
#




# kcmodule -C "first of many module changes for vPars/Oracle/Peoplesoft 
               config" idds=best

NOTE:    The configuration being loaded contains the following change(s)
         that cannot be applied immediately and which will be held for
         the next boot:
      -- The configuration is supposed to include a module 'idds' which
         is not available without a kernel rebuild.
       * The automatic 'backup' configuration has been updated.
       * Building a new kernel for configuration 'nextboot'...
       * Adding version information to new kernel...
       * The requested changes have been saved, and will take effect at
         next boot.
Module               State   Cause
idds    (now)        unused
        (next boot)  static  explicit
#

This tunable is dynamic, so the change was made immediately as you can see at the bottom of the listing with now. The kcmodule command changed idds; however, this will be applied at next boot, as shown in the following kconfig command:

# kconfig -D
Module               State   Cause
idds    (now)        unused
        (next boot)  static  explicit
NOTE:    There are no tunable changes being held until next boot.
#

In both the kctune and kcmodule commands, I preceded the change with a comment (-C) that appears on the /var/adm/kc.log file.

For the module change to take place, a reboot is required. After the reboot takes place, I again issue the kcmodule command to show that the idds change has been incorporated into the new current kernel:

# kcmodule -d idds
Module  State   Cause
    Description
idds    static  explicit
    Intrusion Detection Data Source
#

You would probably make more changes to the kernel than the two used in this example. After the changes are made, you would save the update configuration with the kconfig command:

# kconfig -C "Rev1 of vPars/Oracle/Peoplesoft kernel configuration" 
 -s rev1_vPars_oracle_peoplesoft

       * The current configuration has been saved to
         'rev1_vPars_oracle_peoplesoft'.

# ll /stand
total 96992
drwxr-xr-x   5 root   sys     8192 Sep 21 09:38 Initial_vPars_Oracle_Peoplesoft
drwxr-xr-x   5 root   sys     8192 Sep 21 10:34 backup
dr-xr-xr-x   3 bin    bin       96 May  5 15:46 boot.sys
-rw-r--r--   1 root   sys       21 May  5 15:44 bootconf
lrwxr-xr-x   1 root   root      14 Sep 21 10:51 bootfs -> current/bootfs
drwxr-xr-x   5 root   root    8192 May 25 12:03 crashconfig
drwxr-xr-x   5 root   sys     8192 Sep 21 10:34 current
drwxr-xr-x   5 root   sys     8192 Sep 19 15:38 initial_11iv2
drwxr-xr-x   5 root   sys     8192 Sep 12 20:28 installed
-rw-r--r--   1 root   sys    16024 Sep 21 10:52 ioconfig
-r--r--r--   1 root   sys       82 May  5 16:11 kernrel
drwxr-xr-x   2 root   sys       96 Sep 21 10:56 krs
drwxr-xr-x   5 root   sys     8192 May  5 16:12 last_install
drwxr-xr-x   2 root   root      96 May  5 15:43 lost+found
lrwxr-xr-x   1 root   root       7 Sep 21 10:51 nextboot -> current
drwxr-xr-x   5 root   sys     8192 Sep 21 11:06 rev1_vPars_oracle_peoplesoft
-rw-------   1 root   root      12 Sep 21 10:51 rootconf
lrwxr-xr-x   1 root   root      15 Sep 21 10:51 system -> nextboot/system
-r--r--r--   1 root   sys     1996 May  5 16:01 system.import
-rw-r--r--   1 root   sys     2537 May  5 16:51 system.prev
-rwxr-xr-x   3 root   sys 49536344 Sep 21 10:34 vmunix
#

The long listing of /stand shows the kconfig command did indeed save the current kernel configuration under the name specified, beginning with rev1. In addition, a new comment in /var/adm/kc.log identifies that this step was taken. Now both the original configuration that was saved earlier and the current configuration exist in /stand.

I don't think you can save your kernel configuration too often. I sometimes make hundreds of kernel configuration parameter changes when I prepare a new system to run a specific application, so I'm careful to save my kernel before making these many changes. The only problem with saving many kernel configurations is the space consumed in /stand. If you run out of space in /stand it can be difficult to increase it, so you must keep an eye on the available space in /stand.

You may find yourself in a situation where you have to boot a saved kernel configuration, which is covered in the next section.

Reverting to a Saved Kernel Configuration

Although the two configuration changes made in the previous section were trivial if, for any reason, you need to revert to a saved kernel configuration you can do so. The easiest way to do this is to run kconfig -n oldconfig. An alternative is to load the saved configuration at the time of boot. In the following example, I could revert back to Initial_vPars_Oracle_Peoplesoft or initial_11iv2 which were saved in /stand. To revert to this kernel configuration issue the following command at the HP-UX prompt on an Itanium system running EFI:

Please select a boot option

    HP-UX Primary Boot: 0/0/0/2/0.6.0
    Acpi(000222F0,0)/Pci(1|0)/Mac(00306E4B9AD9)
    Acpi(000222F0,100)/Pci(1|0)/Mac(00306E4BAA28)
    EFI Shell [Built-in]
    Boot option maintenance menu


    Use ^ and v to change option(s). Use Enter to select an option
Loading.: HP-UX Primary Boot: 0/0/0/2/0.6.0
Starting: HP-UX Primary Boot: 0/0/0/2/0.6.0

(c) Copyright 1990-2003, Hewlett Packard Company.
All rights reserved

HP-UX Boot Loader for IPF  --  Revision 1.73

Press Any Key to interrupt Autoboot
\EFI\HPUX\AUTO ==> boot vmunix
Seconds left till autoboot -   9
   Type 'help' for help

HPUX> boot initial_11iv2

From EFI, I select the HP-UX Primary Boot and then interrupt the boot. At this point, I enter initial_11iv2 as the configuration to load.

On a PA-RISC system, this old configuration would have been entered at the ISL prompt with ISL> hpux config_name vmunix.

System File

Although the kernel commands covered support modifying your configuration and building a new kernel, you can still use /stand/system or the system file for any kernel configuration. There is a system file in the directory for all the kernel configurations that you've built on your system. These can be exported from one system and imported to another system in order to replicate a kernel configuration that you like onto another system. You can, for example, export a configuration with kconfig -e name on one system, import a configuration on another system with kconfig -i name, and thereby replicate a configuration on another system.

Device bindings are also managed in the system files. Device bindings are configuration settings that have to do with specific hardware devices such as primary swap (swap lines in the system file), dump devices (dump in the system file). and device driver (device in the system file) specifications.

Another common use of system files is to make multiple changes in the system file and have all the changes take effect on the next reboot.

The following is an abbreviated system file showing some of the lines in the currently running system file:

# example system file 

* Module entries
*
module prm best [3F56E2F0]
module ipf loaded 0.1.0
module mpt best [40075F90]
module vols best [3F41B706]
	.
	.
	.
* Swap entries
*
*
* Dump entries
*
dump lvol
*
* Driver binding entries
*
*
* Tunables entries
*
tunable nproc 4200
tunable shmmax 68719476736
tunable semume 512
tunable semmnu 4092
tunable semmns 8192
tunable maxfiles 8192
tunable maxfiles_lim 8192
	.
	.
	.

This listing shows module, swap (none present), dump, and tunable entries.

You could update numerous entries in the system file. Issue kconfig -i system_file_name and reboot this system to incorporate the changes incorporated into the running kernel, as shown in the following listing:

# kconfig -i /stand/Initial_vPars_Oracle_Peoplesoft/system
WARNING: The automatic 'backup' configuration currently contains the
         configuration that was in use before the last reboot of this
         system.
     ==> Do you wish to update it to contain the current configuration
         before making the requested change? y
       * The automatic 'backup' configuration has been updated.
NOTE:    The configuration being loaded contains changes that cannot be
         applied immediately:
NOTE:    The changes will be held for next boot.
       * /stand/Initial_vPars_Oracle_Peoplesoft/system has been
         imported.  The changes will take effect at next boot.
[rx8620b{root}:/]>

The kconfig command updates the currently running kernel. The changes can not be applied immediately, so a reboot is required. The file /stand/current/system reflects the changes that you made to the configuration. You can also give a name to the updated configuration so that a new configuration is produced, as shown in the next example.

You can also make changes to /stand/current/system and save the configuration to a specific name, as shown the following example:

# kconfig -i test2 /stand/current/system
WARNING: The system file was created from the configuration 'nextboot'.
         The import operation is targeted at 'test2'.
     ==> Do you wish to continue? y
       * /stand/current/system has been imported to 'test2'.
#

Prior to running this kconfig command, I update /stand/current/system with numerous changes. The changes were made immediately and no reboot was required for these dynamic changes to take effect. This kconfig command imports the system file and saves it to configuration called test2. This results in a test2 directory in /stand, as shown in the following listing:

# ll /stand/test2
total 96784
-rw-r--r--   1 root       sys              0 Sep 25 11:24 .config
-rw-r--r--   1 root       sys            147 Sep 25 11:24 README
drwxr-xr-x   3 root       sys             96 Sep 25 11:24 bootfs
drwxr-xr-x   2 root       sys             96 Sep 25 11:24 krs
drwxr-xr-x   2 root       sys             96 Sep 25 11:24 mod
-rw-r--r--   1 root       sys           2902 Sep 25 11:24 system
-rwxr-xr-x   5 root       other      49534656 Jun 15 15:49 vmunix
#

This results in a saved configuration reflecting the changes that have been made. This configuration has been saved and can be loaded anytime.

The mk_kernel -s system_file_name command can also build the new kernel. mk_kernel is fully supported and is great for those of us who have used this command in past releases of HP-UX.

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