sys_attrs - introduction to kernel subsystem attributes used for configura-
tion and tuning
The operating system kernel is built from many mandatory and optional sub-
systems. 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. 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 Environ-
ment (CDE), you can run the dxkerneltuner application to get the same
You can use the dxkerneltuner application or the /sbin/sysconfig -r command
to change attributes for a kernel subsystem. For some subsystems, attribute
values are best 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
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 tun-
ing 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, requir-
ing (in some cases) careful manipulation of an entire set of attri-
butes 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
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 sup-
port 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 archi-
tectures, 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 documenta-
tion. 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.
+ The kernel software no longer uses parameter values in the
Some attributes used to have corresponding parameters in the
/usr/sys/conf/param.c file, which system administrators were accus-
tomed 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 /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 or used during kernel
configuration. Therefore, a param.c file migrated from a release prior
to Version 5.1A has no effect on kernel behavior.
Attribute names are, in some cases, different from parameter names.
Furthermore, starting with Tru64 UNIX Version 5.1A, no attribute names
contain hyphens; the names are either all letters and numbers or con-
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 reference pages for technically required subsys-
tems. 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
Network Administration: Connections
Network Administration: Services