sys_attrs_proc man page on DigitalUNIX

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sys_attrs_proc(5)					     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 applica‐
	      tions  that  use	more than 600 seconds of CPU time to automati‐
	      cally increase their nice values (that is, lower their  schedul‐
	      ing 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	auton‐
	      ice_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
	      autonice_penalty attribute.

	      Default value: 600 (seconds)

	      Minimum value: 0

	      Maximum value: 86,400

	      A	 value	that  enables  (1) or disables (0) the ability of user
	      processes to create core dumps. If disabled (0), this  attribute
	      can  prevent some denial-of-service attacks that are possible if
	      the core file and the directory where it is written  are	inade‐
	      quately  protected and a privileged user is running the program.
	      By default, many applications dump core files to	the  directory
	      from  which  the	user invoked the program. If a privileged user
	      invoked such a program from a world-writeable directory, such as
	      /tmp,  the  /tmp/core pathname could be spoofed into creating or
	      overwriting a file in a privileged location.

	      Default value: 1 (enabled)

	      Because core files provide important  debugging  information  to
	      application  maintainers,	 it is recommended that this attribute
	      be set to 0 (disabled) only if the system is subject to  denial-
	      of-service attacks.

	      This attribute can be modified at run time.

	      Note  that  programs  can	 control the location of core files by
	      using the setsysinfo() call with	an  SSI_COREDIR	 request.  See
	      setsysinfo(2) for more information.

	      A value that enables (1) or disables (0) the ability of applica‐
	      tions running in setuid/setgid mode to dump core.

	      Default value: 0 (disabled)

	      Core dumps from processes of applications running in setuid/set‐
	      gid mode can contain sensitive information that might be used to
	      compromise  system  security.  It	 is  recommended   that	  this
	      attribute be set to 1 (enabled) only for purposes of application
	      debugging and then returned to 0 (the default) after the	appli‐
	      cation is debugged.

	      This attribute can be modified at run time.

	      The  maximum number of unique core files that a program can cre‐
	      ate 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  cre‐
	      ated.

	      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_disable_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 com‐
	      mand 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 dynamic value that controls the allocation of memory with both
	      write  and  execute  privileges  in  order  to reduce privileged
	      process vulnerability to buffer  overflow	 exploits.   All  pro‐
	      cesses may allocate writable and executable memory.

	      Default value: 0 (disabled)

	      Minimum value: 0

	      Maximum value: 53

					  Caution

	      Before changing executable_data from the default value of 0, you
	      must run the /usr/sbin/javaexecutedata script. Otherwise, privi‐
	      leged java applications will fail in unpredictable ways.

	      This  attribute  can be set to only one of five values. The fol‐
	      lowing list shows the five values	 and  describes	 what  happens
	      when  a  process executing as root or a process running a setuid
	      application requests writeable, executable memory:  The  request
	      succeeds,	 and the process may allocate writeable and executable
	      memory.  The request succeeds, but  the  process	receives  only
	      writeable	 memory.  No  message is generated. This is the recom‐
	      mended value.  The request fails with an EACCES status. No  mes‐
	      sage  is	generated.   The  request  succeeds,  but  the process
	      receives only writeable memory. A	 message  is  generated.   The
	      request fails with an EACCES status, and a message is generated.

	      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 pro‐
	      gram 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 vulner‐
	      able 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	opera‐
	      tion.  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: 256 (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: 1024 (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 sys‐
	      tem 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 values 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 docu‐
	      mentation.

	      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	 docu‐
	      mentation.  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 set‐
	      sysinfo() 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
	      number  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
	      priority 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
	      typically 1024 or 1200. (To determine the hz value on a particu‐
	      lar  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 exam‐
	      ple, 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 multi‐
	      processor system before it is eligible  to  migrate  to  another
	      processor.

	      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)
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