sys_attrs_proc(5) File Formats Manual sys_attrs_proc(5)
NAME
sys_attrs_proc - system attributes for the proc kernel subsystem
DESCRIPTION
This reference page describes system attributes for the Process (proc) kernel subsystem. See sys_attrs(5) for an introduction to system
attributes.
Do not edit the system configuration file to directly change the value of system parameters; use the dxkerneltuner application, the
/sbin/sysconfig -r command, or the sysconfigdb command to make such changes. See dxkerneltuner(8), sysconfig(8), and sysconfigdb(8) for
more information about your options for configuring kernel subsystems.
Attributes whose names are preceded by an asterisk(*) can be modified at run time.
A value that enables (1) or disables (0) the ability of applications that use more than 600 seconds of CPU time to automatically
increase their nice values (that is, lower their scheduling priorities).
Default value: 0 (disabled)
The nice value that is assigned to a process after it has used an amount of CPU time that exceeds the value of the autonice_time
attribute.
Default value: 4
Minimum value: 0
Maximum value: 20
The amount of CPU time, in seconds, that a process can use before it is assigned the nice value that is specified by the auton-
ice_penalty attribute.
Default value: 600 (seconds)
Minimum value: 0
Maximum value: 86,400
The maximum number of unique core files that a program can create on a host system.
Default value: 16 (files)
Minimum value: 1
Maximum value: 99,999
This attribute can be modified at run time.
A value that enables (1) or disables (0) creation of multiple versions of core files. If this attribute is set to 0, an existing
core file will be overwritten when a new one is created.
Default value: 0 (disabled)
This attribute can be modified at run time.
A value that enables (1) or disables (0) a limit on the number of arguments that a command can have when it executes. When exec_dis-
able_arg_limit is set to one, there is no limit on the number of command arguments other than a memory restriction imposed by the
user program stack size.
Default value: 0 (hard limit enforced)
This attribute can be modified at run time. It is recommended that you set exec_disable_arg_limit to 1. The default value is in
place because industry standards currently require not only that a hard limit be accessible to any programs executing a command but
also that an error be returned to the program when this limit is reached. When exec_disable_arg_limit is set to 1, the operating
system does not return an error because there is no hard limit to enforce. Most programs that conform to industry standards will
continue to execute correctly if this error is not returned.
A value that allows (1) or disallows (0) execute privilege on the user program stack for programs that would otherwise have this
privilege. Disallowing execute privilege on the user program stack enhances system security but does not affect normal programs.
Default value: 0 (disallowed)
This attribute can be modified at run time. Although certain applications may require the program stack to be executable, it is
strongly recommended that you set executable_stack to 1 only on systems (such as those behind firewalls) that are not vulnerable to
security violations.
A value that enables (1) or disables (0) booting the priority of processes that have recently awakened from a block I/O operation.
Setting this attribute to 1 reduces I/O latency and may make the system more responsive.
Default value: 1 (enabled)
Maximum amount, in bytes, of user process address space.
Default value: 4,294,967,296 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
Maximum size, in bytes, of a data segment for each process.
Default value: 1,073,741,824 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
Maximum size, in bytes, of a user process stack.
Default value: 33,554,432 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
Maximum number of processes (tasks) that a user can create. (The superuser is not affected.)
Default value: 64 (processes)
Minimum value: 0
Maximum value: 524,287
If you specify 0 for this attribute, the system does not check how many processes a user creates.
Maximum limit of threads a user can create. (The superuser is not affected.)
Default value: 256 (threads)
Minimum value: 0
Maximum value: LONG_MAX
If you specify 0 for this attribute, the system does not check how many threads a user creates.
Number of simultaneous users that a system can support without straining system resources. System algorithms use the maxusers value
to size various system data structures and to determine the amount of space allocated to system tables, such as the system process
table.
Default value: System dependent
Minimum value: 8 (users)
Maximum value: 16,384
Increasing the value of the maxusers attribute allocates more system resources to the kernel. However, it also increases the amount
of physical memory consumed by the kernel. Changing the value of the maxusers attribute automatically adjusts the values of other
attributes, including the taskmax, threadmax, and min_free_vnodes attributes if you have not explicitly overridden the default val-
ues for those attributes.
The maxusers value can be increased at run time. It can be decreased only at boot time.
Minimum amount of memory that can be used for timeout tables. The value of this attribute is automatically adjusted.
Do not modify the default setting for this attribute unless instructed to do so by support personnel or by patch kit documentation.
The number of callout tables. This number determines the size of the hash table for timeout queues.
Default value: The number of process slots divided by 32
Do not modify the default setting for this attribute unless instructed to do so by support personnel or by patch kit documentation.
The size of the hash table for the wait queue.
Default value: The number of process slots divided by 32
Minimum value: 64
Maximum value: 262,143
Hard limit for the number of file descriptors for each process.
Default value: The value of OPEN_MAX_SYSTEM, which is 4096 (file descriptors)
Minimum value: 0
Maximum value: 65,536
If the number of file descriptors reaches the value of the open_max_hard attribute or higher, the process is stopped. The value for
this limit can be increased only in a program. Use the getdtablesize() system call to obtain the total number of file descriptors in
a process' descriptor table. You can determine the current open_max_hard limit by using the getrlimit() system call and increase the
hard limit for a process by using the setsysinfo() function with the SSI_FD_NEWMAX option.
The soft limit for the number of file descriptors for a process.
Default value: The 4096 (file descriptors)
Minimum value: 0
Maximum value: open_max_hard
When the open_max_soft limit is reached, a warning message is issued. Use the getdtablesize() system call to obtain the total num-
ber of file descriptors in a process' descriptor table. You can determine the open_max_hard and open_max_soft limits by using the
getrlimit() system call and increase the soft limit for a process up to its hard limit by using the setrlimit() system call.
The maximum amount, in bytes, of user process address space.
Default value: 4,294,967,296 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
Current maximum size, in bytes, of a data segment for each process.
Default value: 134,217,728 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
The maximum size, in bytes, of a user process stack.
Default value: 8,388,608 (bytes)
Minimum value: 0
Maximum value: 4,398,046,511,104
A value that determines (per second of CPU time) the number of context switches that can occur between processes with the same pri-
ority and the timeslice allotted to each process.
Default value: 0 (100 context switches per second)
Minimum value: 0
Maximum value: hz
The system uses the following formula to compute timeslice:
timeslice = hz / number_context_switches
The hz value is the timer interrupt frequency (hertz) for one second of CPU time. This value is dependent on hardware and is typi-
cally 1024 or 1200. (To determine the hz value on a particular system, programmers can use the getsysinfo() call with GSI_CLK_TCK as
the op parameter.)
If round_robin_switch_rate is either 0 (zero) or greater than hz, the system uses 100 for number_context_switches. For example, if
hz is 1024, the resulting timeslice is 10 milliseconds, and if hz is 1200, the resulting timeslice is 12 milliseconds:
timeslice = 1024 / 100 = 10
timeslice = 1200 / 100 = 12
If round_robin_switch_rate is greater than zero and less than or equal to hz, then number_context_switches is set to
round_robin_switch_rate. For example, changing round_robin_switch_rate from 0 to 20 decreases the number of context switches and
increases timeslice by a factor of five:
timeslice = 1024 / 20 = 51
timeslice = 1200 / 20 = 60
Context switching carries a certain amount of CPU overhead. If a CPU consistently handles many large jobs that do not complete
quickly, a larger timeslice (and fewer context switches) may improve throughput. However, the tradeoff is reduced response time for
any interactive processes that the CPU handles.
Time, in clock ticks, that a thread must remain idle on a multiprocessor system before it is eligible to migrate to another proces-
sor.
Default value: 0 (clock ticks)
Minimum value: 0
Maximum value: INT_MAX
This attribute is used to tune the soft affinity algorithm on multiprocessor systems. Soft affinity enables a process to stay where
it last ran, and thereby optimize its use of any data or instructions that it had brought into cache memory. The sched_min_idle
attribute is used only on multiprocessor systems; it has no effect on single-CPU systems.
SEE ALSO
Commands: dxkerneltuner(8), sysconfig(8), sysconfigdb(8)
Others: sys_attrs(5)
System Configuration and Tuning
sys_attrs_proc(5)