sys_attrs(5)sys_attrs(5)NAMEsys_attrs - introduction to kernel subsystem attributes used for con‐
figuration and tuning
DESCRIPTION
The operating system kernel is built from many mandatory and optional
subsystems. If you are logged into the root account, the following com‐
mand 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 infor‐
mation 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 Commu‐
nication (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 sys‐
tem 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 pre‐
cedes the names of these attributes.
NOTES
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 manu‐
ally.
Most of the attributes that are modifiable at run time have been
implemented this way for ease of system tuning. Others are modi‐
fiable 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 rea‐
son, 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 nec‐
essary, 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 sub‐
sets 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.
SEE ALSO
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)