System Configuration File

The system configuration file contains two primary elements:

• Instructions used by the utility / etc/ config to build

• Dependencies used to compile and link a new kernel

You can build a new kernel automatically by using the utility / etc/ doconfig, or manually by using /etc/config and a series of other steps. For more information about the procedure used to build a new kernel, see the Guide to Configuration File Management.

4.1.1 Global Definitions

You can locate global definitions in the first part of the configuration file.

Global definitions convey information to the kernel building process in the following ways:

• Flags to include some optional code segments

• Indicators of physical features of the machine or its environment

• Values of parameters that can be set optionally at compile time

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Examples of parameters used as flags are machine and cpu. The machine parameter defines the hardware architecture of the workstation, the parameters vax or mips, for example. The cpu parameter describes the processor class or processor name.

Parameters that describe the physical features of the machine or its

The value of processors defines the number of CPUs making up the system.

scs_sysid

The value of scs sysid identifies each host uniquely on the CI star cluster to the SCS subsystem.

timezone

Setting the timezone allows the system clock to display the correct time (standard time and daylight savings time) for your location.

The remaining global definitions in the configuration file are used to compute sizes of various internal kernel tables or to set minimum and maximum sizes of several memory allocation parameters. These parameters are maxusers, maxuprc, maxuva, bufcache, swapfrag, maxtsiz, maxdsiz, maxssiz, physmem, smrnin, smmax, smseg, smbrk, and smsmat. The parameters maxdsiz and maxssiz in ULTRIX Version 4.0 replace the parameters dmmin and dmmax in earlier versions.

The maxusers parameter is used in several computations, but most importantly it is used to compute the size of the system process table. The maxuprc parameter controls the maximum number of processes one user can run simultaneously. An internal algorithm using the values of maxusers and maxuprc determines the size of the system process table. The size of the system process table controls the maximum number of processes that can be run at anyone time.

The parameters maxuva, maxtsiz, maxdsiz, maxssiz, smmin, smmax, smseg, smbrk, and smsmat are all concerned with different aspects of the manner in which memory is allocated. The maxuva and maxt s i z parameters set system-wide virtual address space for users and the size of the largest text segment, respectively. The maxdsiz parameter defines the largest data segment, in megabytes, allowed by the system; the default value is 32 MB.

The maxssiz parameter defines the largest stack segment, in megabytes, allowed by the system; the default is 32 MB. The parameters beginning with the sm prefix control various aspects of shared memory.

The physmem parameter sets the amount of the system's physical memory.

The system uses this when the kernel is built to determine the size of system page table. Set the physmem parameter value equal to the actual amount of physical memory. Setting physmem larger or smaller than the size of physical memory decreases the amount of memory available to applications.

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The parameter bufcache is used to change the size of the buffer cache when the kernel is built. The default value of 10 percent is used if bufcache does not appear in the configuration file. The parameter swapfrag satisfies requests for additional swap space using the value supplied; the default is 64. Thus, a process requesting additional swap space will be allocated 64 512-byte blocks.

The last set of parameters appearing in the global definitions are options flags. By specifying these flags, different optional sections of code are linked with the kernel when built. These options include the parameters INET

and DECNET for internet communications protocol and the DECnet layered product, respectively. If the kernel being built does not implement some of these options, you can delete their options flags in the configuration file. The text size of the resulting kernel is smaller.

4.1.2 System Image Definitions

The system image definition section of the configuration file consists of lines beginning with the keyword config. A separate kernel is generated for each config line. Normally, only one config line exists in the configuration file.

The following keywords control the generation of the system image:

• root specifies the disk partition on which the root file system is found

• swap identifies the disk partition or partitions which are used for the swapping and paging area

• dumps specifies the disk partition on which crash dumps are stored 4.1.3 Device Definitions

The device definitions section of the configuration file contains a line describing each hardware component connected to the system or hardware that can be connected to the system in the future. That is, the device specified in the configuration file does not have to be present. The keywords that define the device types are adapter, master, controller, device, disk, and tape. The format for fields in each of the device definitions is dependent on the device type.

4.1.4 Pseudodevice Definitions

The pseudodevice definitions section of the configuration file is the link between the device definitions section, which specifies the hardware controllers, and the equipment connected to those controllers. The pseudo-device keyword is followed by a name that specifies the identifier for the device driver. The device driver code is compiled (if necessary) and linked with the kernel to give access to that device. The doconfig utility also uses this section to create the device-special files needed by the kernel to interface with the hardware attached to the system.

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