kctune.1m (2010 09)

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kctune(1M) kctune(1M)
a new user-defined tunable. This tunable will not directly affect the kernel, but may be
used in expressions defining the values of other tunables. The
-u option is not needed
when changing the value of a user-defined tunable; it is needed only to create one.
To remove a user-defined tunable, set it to
Default. A user-defined tunable cannot be
removed if it is used in the expressions defining any other tunable values.
-v Includes verbose information about the tunable parameters in the output listing. The
information includes the name and value of the tunable, a short description, its allowed
values, its dependencies on other tunables and restrictions on when the tunable values
can be changed. Not valid in combination with
-d, -g,or-P.
Operands
The operands to
kctune may be any mixture of tunable queries and assignments. The operands must
each take one of the forms listed below. No spaces are permitted within each operand. If no operands
are given, kctune performs a query on all tunables (subject to the constraints of the
-D or -S flags).
tunable Reports the value of the tunable. No change is made.
tunable
= Sets the tunable to its default state.
tunable
=Default Sets the tunable to its default state. The word
Default is not case sensitive.
tunable
=expr Sets the tunable to to the specified expression. See Expressions below for details.
tunable
+=value Increases the tunable by the specified value . value must be an integer constant
(not an expression). C syntax for octal and hexadecimal constants is supported.
tunable
>=value Sets tunable’s value to value , unless it is already greater. value must be an
integer constant (not an expression). C syntax for octal and hexadecimal con-
stants is supported. Note that the operand will probably need to be quoted to
avoid interpretation by the shell.
Expressions
Tunables can be set to expressions following the expression syntax of the C programming language, with
the following adjustments:
• All constants must be integers, following the C language syntax for integer constants. Hexade-
cimal constants must be prefixed with
0x and octal constants with 0. For convenience, the fol-
lowing symbols can be added to the end of an integer constant:
k Multiplies the constant by 1000 (10ˆ3).
kB Multiplies the constant by 1024 (2ˆ10).
M Multiplies the constant by 1,000,000 (10ˆ6).
MB Multiplies the constant by 1,048,576 (2ˆ20).
GB Multiplies the constant by 1,073,741,824 (2ˆ30).
• Identifiers in the expression must be the names of other tunables. Some tunables cannot be used
in expressions.
• Some tunables accept expressions in the form of a constant followed by a percent sign (
%). Such
expressions indicate that the tunable should be set to a percentage of some system resource;
when the resource grows or shrinks, the effective value of the tunable changes to maintain the
specified percentage. Consult the man pages for specific tunables to determine whether they
support percentage values and how they are used.
As in the C programming language, expression evaluation is subject to rollover, overflow and underflow.
Setting unsigned tunables to an expression that evaluates to a negative quantity will have unpredictable
results.
When passed on a command line, expressions may need to be quoted to avoid interpretation by the shell.
Expressions are evaluated only when one of the kernal configuration commands is running. If a tunable’s
value changes under other circumstances, expressions involving this tunable are not re-evaluated and the
tunable values dependent on those expressions are not updated. For example, this can happen when tun-
ables are changed using a direct call to
settune() or settune_txn(), or when a tunable is reset to
its default value during boot because of a validation failure.
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: September 2010