kctune(1M)kctune(1M)NAMEkctune - 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 val‐
ues.
Options
Specifies whether or not to update the automatic
configuration before the requested change. Also speci‐
fies 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 configu‐
ration.
See kconfig(5) for more information on saved kernel con‐
figurations.
The specified comment will be included in the kernel configuration log
file entry made for this invocation of For more details
on the kernel configuration log file, see kclog(1M).
Note that it will usually be necessary to quote the com‐
ment 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 tun‐
able will not directly affect the kernel, but may be
used in expressions defining the values of other tun‐
ables. 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 defining 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 restric‐
tions 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 spaces
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 hexadeci‐
mal 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:
· All constants must be integers, following the C language syn‐
tax 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 con‐
stant:
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).
· Identifiers in the expression must be the names of other tun‐
ables. 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 per‐
centage. 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 unpre‐
dictable 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 val‐
ues 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 tunables
change their default values in response to changing system workloads.
These tunables are called "Automatic" tunables and are marked in out‐
put.
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 tun‐
able'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 when‐
ever 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 output 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 oth‐
erwise.
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 spec‐
ified using an expression, this field contains the result of
evaluating that expression. This field is present only for tun‐
ables 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 invoca‐
tion of or an otherwise. This field is present only for tun‐
ables 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 con‐
taining 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
expression, 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 config‐
urations.
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 mean‐
ing that the administrator is allowing the system to choose the tunable
value. The changes column shows the restrictions on when the tunable
value can be changed. Tunables whose value can be changed immediately
are marked Tunables whose values are being automatically tuned by the
system are marked If the administrator has disabled the automatic tun‐
ing 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 cur‐
rently 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 tun‐
able 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 ALSOkclog(1M), gettune(2), settune(2), settune_txn(2), tuneinfo2(2), kcon‐
fig(5).
available on
kctune(1M)
