sys_attrs - introduction to kernel subsystem attributes
used for configuration and tuning
The operating system kernel is built from many mandatory
and optional subsystems. If you are logged into the root
account, the following command lists the subsystems
included in the kernel for your system: # /sbin/sysconfig
-s
The majority of the kernel subsystems have sets of
attributes whose values control different aspects of subsystem
configuration. These attributes reside in the
/etc/sysconfigtab database. You can examine the names,
the current settings, and (if applicable) the minimum, and
maximum settings of attributes for a particular subsystem
by using the /sbin/sysconfig command. The -q option followed
by the subsystem name displays attribute names and
current settings. The -Q option followed by the subsystem
name displays minimum and maximum settings and the kinds
of operations permitted on the attribute (Configurable (at
boot time), Reconfigurable (at run time), Query only). In
the Common Desktop Environment (CDE), you can run the dxkerneltuner
application to get the same information.
You can use the dxkerneltuner application or the
/sbin/sysconfig -r command to dynamically change
attributes for a kernel subsystem. For settings that persist
across system boots, attribute values are applied
through a stanza-formatted file that is specified as an
argument to the sysconfigdb command.
See dxkerneltuner(8), sysconfig(8), and sysconfigdb(8) for
more information about your options for configuring kernel
subsystems.
The following subsystems must be included when the kernel
is built: Configuration Manager (cm) Generic Kernel
(generic) Interprocess Communication (ipc) Process (proc)
Virtual File System (vfs) Virtual Memory (vm)
A kernel also includes a processor-specific subsystem
whose name is an internal code for a particular processor.
Processor-specific subsystems typically have no
attributes, are not modified directly by users, and are
not documented.
Other kernel subsystems are technically optional, although
a kernel almost always includes quite a few optional subsystems
in order for a system to be useful. For information
on the attributes for a particular subsystem, refer
to the reference page for that subsystem. The names of
these reference pages adhere to the format sys_attrs_subsystem-name.
For example, to see the reference page that
lists and describes attributes for the generic subsystem,
you can type man sys_attrs_generic at the system command
line.
For guidelines on changing kernel subsystem attributes to
improve system performance, see the System Configuration
and Tuning manual. Any discussion about changing
attributes for reasons other than tuning is located in the
appropriate administration or program debugging manual.
You can adjust some subsystem attribute values at run
time. If so, the attribute descriptions mention that fact.
To make it easy for you to locate these attributes when
scanning lists, an asterisk (*) also precedes the names of
these attributes.
When changing kernel attributes, keep in mind the following
points: Many attributes should not be touched.
A relatively small number of the attributes listed
by the sysconfig utility or dxkerneltuner application
should actually be changed and, if they are
changed, only as part of the system configuration
and tuning tasks done by an experienced system or
network administrator. The setting of most subsystem
attributes should be done indirectly through
system and network setup applications or be automatically
adjusted by the kernel. This fact is very
important to remember because attribute settings
can have complex interrelationships with one
another, requiring (in some cases) careful manipulation
of an entire set of attributes rather than
only one. Furthermore, default settings of some
attributes should never be touched, except by support
personnel or by an administrator acting on
instructions from support personnel or patch kit
documentation. A few attributes that are reconfigurable
at run time should not be modified manually.
Most of the attributes that are modifiable at run
time have been implemented this way for ease of
system tuning. Others are modifiable at run time
only because of a software requirement and should
not be changed manually. In general, do not change
the default value of any system attribute manually
unless the system documentation or your support
representative provides directions for changing it.
Attributes are volatile.
System attributes are volatile, such that their
effect, values, and existence can change from one
release to another. This volatility is related to
changes in kernel algorithms that make the system
more self-adjusting, changes in the internal
buffers and queues used by kernel software, the
need to support new platforms and device architectures,
and so forth. For this reason, attribute
settings that worked well on one version of the
operating system or on a different hardware platform
should not be simply carried forward after a
system upgrade. Doing so might not deliver the
results you expect and might even degrade system
performance. It is recommended that system upgrades
be tested with default attribute settings in place
and then tuned, as necessary, according to the most
current system documentation. The best procedure to
use when tuning is to tune one subsystem at a time.
Check the performance effects of your attribute
changes in each subsystem before changing
attributes in another subsystem. Some attribute
names contained hyphens in previous releases and
now contain underscores. However, when processing
an attribute name, the system accepts underscores
and hyphens as equivalent characters. The
/usr/sys/conf/param.c file is obsolete.
Some attributes used to have corresponding parameters
in the /usr/sys/conf/param.c file, which system
administrators were accustomed to editing
directly in Tru64 UNIX Version 4.0D and prior
releases. The operating system software changed
over the course of subsequent releases to reduce
its reliance on the /usr/sys/conf/param.c file.
Starting with Tru64 UNIX Version 5.1A, the
/usr/sys/conf/param.c file is not created after
subsets are installed. A /usr/sys/conf/param.c file
may still be used to apply configuration parameters
to third-party driver modules that require it; however,
the /etc/sysconfigtab database is now the
recommended repository for configuration and tuning
values that are applied to the operating system at
boot time.
Commands: dxkerneltuner(8), sysconfig(8), sysconfigdb(8)
Others: sys_attrs_cm(5), sys_attrs_generic(5),
sys_attrs_ipc(5), sys_attrs_proc(5), sys_attrs_vfs(5),
sys_attrs_vm(5)
This list includes only the reference pages for technically
required subsystems. The number of subsystems that
can be configured in a kernel is very large, so all system
attribute reference pages are not listed here.
System Configuration and Tuning
System Administration
Network Administration: Connections
Network Administration: Services
Kernel Debugging
sys_attrs(5)
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