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.