kctune(1M) kctune(1M)
NAME
kctune - manage kernel tunable parameters
SYNOPSIS
behavior] config] comment] fmt]
module] fields] [arg]...
DESCRIPTION
is the administrative command for HP-UX kernel tunable parameters. It gives information about tunable parameters and their values, and
makes changes to tunable values.
This command can work with any saved kernel configuration, or with the currently running kernel configuration, depending on the use of the
flag (see below). By default, changes to the currently running kernel configuration are applied immediately. Some changes cannot be
applied without a reboot; if any such changes are requested, or the flag is given, all changes on the command line will be held until next
boot.
Only users with appropriate privileges can make changes to tunable values.
Options
Specifies whether or not to update the automatic
configuration before the requested change. Also specifies the default backup behavior for future changes. See kconfig(5)
for a description of the various backup behaviors. Not valid in combination with
For compatibility with old releases, is accepted as an alias for and is accepted as an alias for These aliases will be
removed in a future release.
will view or change tunables in the saved kernel configuration named
config. If this option is not specified, will view or change tunables in the currently running kernel configuration.
See kconfig(5) for more information on saved kernel configurations.
The specified comment will be included in the kernel configuration log file entry made for this invocation of For more details on the ker-
nel configuration log file, see kclog(1M). Note that it will usually be necessary to quote the comment in order to avoid
interpretation by the shell.
Adds the description of each tunable to the output.
Restricts output to only those parameters which have changes being
held until next boot. will return 1 if there are any such parameters; see below. Not valid in combination with
Formats all tunable values according to the specified format, which must
be one of the characters or representing signed decimal, unsigned decimal, octal, or hexadecimal, respectively. In the
absence of this option, chooses an appropriate format for each tunable.
Group related tunables. The tunables in the output will be grouped and
sorted by the kernel modules that define them. Note: the set of tunables defined by each kernel module may change in future
releases of HP-UX.
Changes will be held until next boot, even if they could be applied
immediately. Not valid in combination with
Tells to include in its output only those tunables which are defined by the specified module.
Tells to include only the specified fields in its output, and to print them in the machine-readable form described in kconfig(5).
See the below. Not valid in combination with or
Only tunables with non-default values will be included in the output.
Not valid in combination with
Allow the creation of user-defined tunables. Normally,
will not accept any tunable name that does not identify an existing tunable. When the option is given, will accept an
assignment to an unrecognized tunable name and use it to define 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 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 A user-defined tunable cannot be removed if it is used in the expressions defin-
ing any other tunable values.
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 or
Operands
The operands to may be any mixture of tunable queries and assignments. The operands must each take one of the forms listed below. No spa-
ces are permitted within each operand. If no operands are given, performs a query on all tunables (subject to the constraints of the or
flags).
tunable Reports the value of the tunable. No change is made.
Sets the tunable to its default state.
Sets the tunable to its default state.
The word is not case sensitive.
Sets the tunable to to the specified expression.
See below for details.
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.
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
constants 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:
o All constants must be integers, following the C language syntax for integer constants. Hexadecimal constants must be prefixed
with and octal constants with For convenience, the following symbols can be added to the end of an integer constant:
Multiplies the constant by 1000 (10^3).
Multiplies the constant by 1024 (2^10).
Multiplies the constant by 1,000,000 (10^6).
Multiplies the constant by 1,048,576 (2^20).
Multiplies the constant by 1,073,741,824 (2^30).
o Identifiers in the expression must be the names of other tunables. Some tunables cannot be used in expressions.
o 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 per-
centage 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 circum-
stances, 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 tunables are changed using a direct call to or or when a tunable is reset to its default value during
boot because of a validation failure.
Default State for Tunables
The default value for a tunable is not necessarily fixed. Default values can change between HP-UX releases, or in patches. Some tunables
have default values that are re-computed at boot time, or when there is a change to the hardware configuration of the system. Some tun-
ables change their default values in response to changing system workloads. These tunables are called "Automatic" tunables and are marked
in output.
When a tunable is set to its value is controlled by the HP-UX kernel, and will be changed whenever the default value for the tunable is re-
computed. Specific behavior of each tunable is described in each tunable's man page. HP recommends that all tunables be set to unless the
default value is known to be unsatisfactory.
Setting a tunable to its default value is not the same as setting it to If the current default value of a tunable is 4000,
will set the tunable's value to 4000 and prevent it from changing when the default value is re-computed.
will set the tunable's value to 4000, and automatically change it whenever the default value is re-computed.
Developer's Note
The layout and content of output may change without notice, except when is specified. Scripts or applications that need to parse the out-
put of are expected to use the option. See kconfig(5) for details.
The fields supported in a request are:
This field contains a if the tunable's default value is automatically computed by the system (and can therefore change over time), or an
otherwise.
The value that was in use for the tunable before the change that
was just made, if known. For saved configurations, the previous value of some tunables may not be known. If the value was speci-
fied using an expression, this field contains the result of evaluating that expression. This field is present only for tunables for
which an immediate value change has been made during the current invocation of
This field contains a
if the tunable was set to its default value before this invocation of or an otherwise. This field is present only for tunables for
which an immediate value change has been made during the current invocation of
The expression for the tunable's value before the change that was
just made, if any. If the tunable was set to default, this field contains the word This field is present only for tunables for
which an immediate value change has been made during the current invocation of
The value of the tunable at the time the system last booted.
This field is not printed for saved configurations.
This field contains a
if the tunable is capable of being automatically tuned, or an otherwise.
This field contains the constraints between this tunable and others.
There may be zero or more values of this field for any tunable.
The current value of the tunable, if known.
For saved configurations, the current value of some tunables may not be known until the configuration is in use. If the value was
specified using an expression, this field contains the result of evaluating that expression. If the tunable is being automatically
tuned, this field contains the value the kernel is currently using.
A short description of the tunable.
This field contains a
if the tunable is set to its default value, or an otherwise. If all three of and are the tunable is being automatically tuned.
The default value of the tunable, if known. For saved configurations,
the default values of some tunables may not be known until the configuration is in use.
This field contains a
if the tunable can be changed without a reboot, or an otherwise.
The expression used to set the value of the tunable, if any.
If the tunable is set to default, this field contains the word
This field contains a hexadecimal representation of the bitmask containing the
and flags, among others. See for definitions of flag values. Additional flag values may be defined in future releases or patches.
The maximum value of the tunable. This is an absolute maximum;
the currently running system may not be able to support values this high. If there is no maximum value, this field will be omitted
from the output.
The minimum value of the tunable. This is an absolute minimum;
the currently running system may not be able to support values this low. If there is no minimum value, this field will be omitted
from the output.
The name of the module supplying the tunable, if any; otherwise, this
field will be omitted from the output.
The name of the tunable.
The value that will be used for the tunable at next boot, if
known. The next boot value of some tunables may not be known until the boot completes. If the value was specified using an expres-
sion, this field contains the result of evaluating that expression. This field is not printed for saved configurations.
This field contains a
if the tunable is set to its default value at next boot, or an otherwise. This field is not printed for
The expression for the tunable's value at next boot, if any. If the
tunable is set to default, this field contains the word If is specified, this field is omitted from the output. saved configura-
tions.
This field contains a
if the tunable values should be treated as signed integers, or an otherwise.
The special field name may be specified to indicate that all defined fields should be included in the output. The output may include
fields not listed in this man page. The fields will be listed in unspecified order.
Additional fields may be added in future releases or patches.
Default Output
When is called with no options, it shows all tunables associated with the kernel modules (as well as the user-defined tunables), their cur-
rent values, expressions used to compute those values, and when changes can be made to these tunables. If there are changes that are being
held for nextboot, they will be shown as well.
On a typical system, the expression for most tunables are marked meaning that the administrator is allowing the system to choose the tun-
able value. The changes column shows the restrictions on when the tunable value can be changed. Tunables whose value can be changed imme-
diately are marked Tunables whose values are being automatically tuned by the system are marked If the administrator has disabled the auto-
matic tuning by the system the tunable is marked The tunables which have nothing in the changes column can only be changed with a reboot.
The layout and content of the default output may change in future releases or patches of HP-UX. Scripts or applications which need to
parse the output of must use the option to obtain output that can be parsed.
RETURN VALUE
returns one of the following values:
0 was successful. If was specified, this return value indicates that there are no tunable changes being held for next boot.
1 was successful. However, there were changes requested to the currently running system which cannot be applied until the system
reboots. Therefore, all of the requested changes are being held until next boot.
If was specified, this return value indicates that there are tunable changes being held for next boot.
2 was not successful.
WARNINGS
always checks the validity of tunable values before applying them to the running system. When tunable value changes are held for next
boot, or made to a saved configuration, some of the validity checks are not performed until the changed configuration is booted. If any
tunable values are found to be invalid, messages will be printed to the system console during the boot process, and the default values for
any affected tunables will be used instead.
EXAMPLES
To see all tunables and their current values:
To see which tunables have new values being held until next boot:
To see verbose information about a tunable:
To set a tunable value on the running system:
To set a tunable value to be used when the system reboots:
To increase a tunable's value by 100:
SEE ALSO
kclog(1M), gettune(2), settune(2), settune_txn(2), tuneinfo2(2), kconfig(5).
available on
kctune(1M)