Configurable Kernel Parameters

Certain kernel operating parameters can be configured to fit specific
system needs, resulting in better performance or more effective
allocation of resources. The ideal value for each parameter is often
determined by the system’s particular hardware configuration, the
specific mix of applications the system runs, and the trustworthiness of
system users ; factors that vary widely from system to system.

HP attempts to provide reasonable default parameter settings, but you
may find it necessary or beneficial to modify these settings to better
suit the needs of your particular system’s users. Use the list below to
obtain detailed information about each configurable kernel parameter.

Note that individual parameters usually pertain to a specific subsystem ;
some are independent, but others are interrelated or interact with each
other. The following list of online help topics for each parameter is
grouped according to subsystem.

Warning

Changing kernel parameters to improper or inappropriate values or
combinations of values can cause data loss, system panics, or other
(possibly very obscure and/or difficult to diagnose) operating
anomalies, depending on which parameters are set to what values.

• Before altering the value of any configurable kernel parameter,
  be sure you know the implications of making the change.
• Never set any system parameter to a value outside the allowable
  range for that parameter (SAM refuses to store values outside of
  the allowable range).
• Many parameters interact, and their values must be selected in a
  balanced way.

Discrepancies

As technological advances expand system size and capabilities, it is not
uncommon for maximum and/or default values of certain parameters to
change between releases or to vary between 32-bit and 64-bit processors.
The information provided in the documents associated with this web page
are believed to be accurate as of the time they were produced. However,
system changes may occasionally result in discrepancies between the
document and what is actually present on your system.

If you encounter any such discrepancies in any stated default or limit
values, consult the files in /etc/conf/master.d on your
system to determine the actual values for your machine.

Accounting Subsystem

• Overview of
  Accounting Suspend and Resume
  • Configurable
    Parameters for Accounting :

    acctsuspend

    suspend accounting

    acctresume

    resume accounting

  • Tutorial :
    Specifying an Accounting Threshold Value

Asynchronous I/O Subsystem

• Asynchronous I/O
  Parameters Overview

  aio_listio_max

  Max number of AIO operations that can be specified in a lio_list() call

  aio_max_ops

  Maximum number of AIO operations that can be queued at any time

  aio_physmem_pct

  Maximum number of AIO operations that can be specified in a lio_list() call

  aio_prio_delta_max

  Maximum slowdown factor ; greatest priority reduction allowed in aiocb’s aio_reqprio field

Dump Parameters

• Kernel-panic dump
  parameters overview

  alwaysdump

  Bit-mask of kernel memory pages included in dumps

  dontdump

  Bit-mask of kernel memory pages excluded from dumps

  initmodmax

  Maximum number of kernel modules saved by system-crash dump

  modstrmax

  Maximum size of the kernel-module savecrash table

Fiber Channel Subsystem

• Overview of
  Fiber Channel Kernel Parameters

  num_tachyon_adapters

  Number of Tachyon adapters installed in the system

  max_fcp_reqs

  Maximum number of concurrent FCP requests allowed on a Tachyon FCP adapter

Mass-Storage Subsystem

• Overview of
  File System Kernel Parameters
• List of
  File System Kernel Parameters
• Configurable File System Buffer-Cache Parameters :

  bufpages

  Pages of static buffer cache

  dbc_min_pct

  Minimum dynamic buffer cache

  dbc_max_pct

  Maximum dynamic buffer cache

  nbuf

  Number of static buffer headers

• Configurable Open or Locked Files Parameters :

  maxfiles

  soft limit for open files

  maxfiles_lim

  hard limit for open files

  nfile

  system-wide open-files limit

  nflocks

  system-wide file-lock limit

  ninode

  Maximum open inodes in memory

• Configurable Asynchronous Write Parameter :

  fs_async

  Enable/disable asynchronous disk writes

• Configurable VxFS (Journaled) File-System Parameter :

  vx_ncsize

  Memory space reserved for VxFS directory path-name cache

Logical Volume Manager (LVM)

• Overview of LVM
  Operation
  • Configurable Parameters
    for Logical Volume Manager

    maxvgs

    maximum volume groups on system

    no_lvm_disks

    no volume groups on system (Series 700 only)

Memory Swap Subsystem

• Overview of Memory
  Paging Parameters
  • Configurable
    Parameters for Memory Paging :

    allocate_fs_swapmap

    fixed or dynamic swap-data-structure allocation

    maxswapchunks

    maximum swap space configurable on the system

    nswapdev

    number of available swap devices

    nswapfs

    number of file systems available for swap

    remote_nfs_swap

    enable/disable swap to remote NFS

    swapmem_on

    enable/disable pseudo-swap reservation

    swchunk

    client swap-chunk size

  • Variable-Page-Size Parameters :

    vps_ceiling

    Maximum system-selected page size in Kbytes

    vps_chatr_ceiling

    Maximum chatr-selected page size in Kbytes

    vps_pagesize

    Default user page size in Kbytes

Process Management Subsystem

• Overview of Process
  Management Parameters
  • Configurable
    Parameters for Process Management :

    maxdsiz

    maximum process data segment size

    maxssiz

    maximum process storage segment size

    max_thread_proc

    maximum number of threads that one process can create

    maxtsiz

    maximum process text segment size

    maxuprc

    maximum number of processes per user

    nkthread

    maximum number of kernel threads allowed on the system at same time

    nproc

    maximum number of processes system-wide

    timeslice

    time slice allocation between competing processes

Character-Mode I/O Streams Parameters

• Overview of
  Character-Mode I/O Streams Parameters

  NSTRBLKSCHED

  Factory use only. Do not change value.

  NSTREVENT

  Maximum number of outstanding streams bufcalls that are allowed to exist at any given time on the system.

  NSTRPUSH

  Maximum number of streams modules that are allowed to exist in any single stream at any given time on the system.

  NSTRSCHED

  Maximum number of streams scheduler daemons that are allowed to run at any given time on the system.

  STRCTLSZ

  Maximum number of control bytes allowed in the control portion of any streams message on the system.

  STRMSGSZ

  Maximum number of bytes that can be placed in the data portion of any streams message on the system.

  nstrpty

  System-wide maximum number of streams-based PTYs that are allowed on the system.

  streampipes

  Force All Pipes to be Streams-Based

System V IPC Shared-Memory Subsystem

• System V Inter-Process
  Communication Mechanisms
  • Overview of
    Message Queue Operation
    • Allocating
      Memory Space for Messages
    • Configurable
      IPC Message Parameters :

      mesg

      Enable/disable IPC messages (Series 700 only)

      msgmap

      message free-space map size

      msgmax

      maximum message size

      msgmnb

      maximum bytes in message queue

      msgmni

      maximum message queues on system

      msgseg

      number of segments in message queue

      msgssz

      message segment size

      msgtql

      maximum total messages on system

  • Overview of
    Semaphore Parameters
    • 
      Configurable IPC Semaphore Parameters :

      sema

      Enable/disable semaphores (Series 700 only)

      semaem

      Semaphore value-change limit

      semmap

      Size of free-semaphore resource map

      semmni

      Maximum semaphores system-wide

      semmns

      Maximum user-accessible semaphores system-wide

      semmnu

      Maximum undos per semaphore

      semume

      Maximum semaphore undos per process

      semvmx

      Maximum allowed semaphore value

  • Overview of
    Shared Memory Operation
    • Configurable
      IPC Shared Memory Parameters :

      shmem

      Enable/disable shared memory (Series 700 only)

      shmmax

      Maximum shared memory segment size

      shmmni

      Maximum segments on system

      shmseg

      Maximum segments per process

VME I/O Subsystem Parameters

• VME optional I/O
  subsystem parameters

  vmebpn_public_pages

  Number of Kernel I/O Space Pages Needed by VME

  vmebpn_sockets

  Socket Domain AF_VME_LINK is Active (Boolean)

  vmebpn_tcp_ip

  Maximum Number of DLPI PPAs

  vmebpn_tcp_ip_mtu

  Maximum PPA transmission unit size in Kbytes

  vmebpn_total_jobs

  Maximum Number of VME Ports Open Concurrently

  vme_io_estimate

  Number of 4-Kbyte kernel I/O space pages needed by VME

Miscellaneous Parameters

• Overview of
  Miscellaneous Parameters
  • Miscellaneous
    Configurable Parameters :

    clicreservedmem

    Bytes of system memory to reserve for cluster interconnect

    create_fastlinks

    Create fast symbolic links

    default_disk_ir

    Immediate reporting for disk I/O

    dst

    Enable/disable daylight-savings time

    eqmemsize

    Size of equivalently mapped memory pool

    ksi_alloc_max

    System-wide limit of queued signals that can be allocated

    ksi_send_max

    Maximum number of queued signals that a process can send and have pending at one or more receivers

    max_async_ports

    System-wide maximum number of ports to the
    asynchronous disk I/O driver that processes can
    have open at any given time

    maxusers

    Maximum expected simultaneous system users

    ncallout

    Maximum number of timeouts allowed

    ncdnode

    Maximum number of open CD-ROM FS nodes

    nclist

    Maximum number of cblocks available for tty/pty I/O

    ndilbuffers

    Maximum open files for Device I/O Library

    npty

    Maximum ptys allowed system-wide

    nstrtel

    Number of Telnet Session Device Files

    o_sync_is_o_dsync

    Enable or disable translation of O_SYNC to O_DSYNC in open() and fcntl() system calls

    pfail_enabled

    Enable power-fail recovery

    public_shlibs

    Allow public protection IDs on shared libraries

    rtsched_numpri

    Number of real-time scheduling priority levels

    scroll_lines

    ITE scroll buffer size

    sendfile_max

    Special parameter for web-servers

    Spinlock Parameters (undocumented)

    timezone

    Specify timezone offset from Universal Coordinated Time

    unlockable_mem

    Memory size reserved for system use

Undocumented Parameters

Some parameters are not documented
for any of various reasons. Some are obsolete, some are associated
with independent software subsystems, some can result in severe system
malfunctions if they are altered without proper understanding, and some
are not supported by SAM.