Unix 2.5 Kernel Data Structures and System Administration

KERNEL DATA STRUCTURES AND SYSTEM ADMINISTRATION 

Kernel Data Structures

Most kernel data structures occupy fixed-size tables rather than dynamically allocated space. The advantage of this approach is that the kernel code is simple, but it limits the number of entries for a data structure to the number that was originally configured when generating the system.

If, during operation of the system, the kernel should run out of entries for a data structure, it cannot allocate space for new entries dynamically but must report an error to the requesting user.

If, on the other hand, the kernel is configured so that it it is unlikely to run out of table space, the extra table space may be wasted because it cannot be used for other purposes. 

Algorithms typically use simple loops to find free table entries, a method that is easier to understand and sometimes more efficient than more complicated allocation schemes.


System Administration

Administrative processes are loosely classified as those processes that do various functions for the general welfare of the user community. 

Such functions include disk formatting, creation of new file systems, repair of damaged file systems, kernel debugging, and others. 

Conceptually, there is no difference between administrative processes and user processes. They use the same set of system calls available to the general community. They are distinguished from general user processes only in the rights and privileges they are allowed. 

Internally, the kernel distinguishes a special user called the superuser, endowing it with special privileges. A user may become a superuser by going through a login-password sequence or by executing special programs.

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