NAME

       prctl - Process operations

SYNOPSIS

       prctl [-v] [-h|--help] [--version] <-q|<options....>> [command]

       where <options> are:

       --unaligned=[silent|signal|always-signal|default]

       --fpemu=[silent|signal|default]

       --mcekill=[early|late|default]

DESCRIPTION

       prctl allows you to query or control certain process behavior.  Supported options are:

       Unaligned  memory  access:  When a process performs an unaligned memory access, by default
       the kernel would emulate the unaligned access correctly and log the  unaligned  access  in
       syslog.  This  behavior  can  be  changed so the kernel could either emulate the unaligned
       access correctly without logging an  error  ("silent")  or  send  SIGBUS  to  the  process
       ("signal" and "always-signal"). "always-signal" is available on ia64 only.

       Floating point assistance faults: when a process encounters a floating point assist fault,
       kernel would invoke floating point emulator and log the floating point assist fault.  This
       behavior  can  be  changed  so  the  kernel  could either emulate floating point operation
       without logging an error ("silent") or send SIGFPE to the offending process ("signal").

       Machine check memory corruption kill policy: If a hardware memeory corruption is  detected
       inside  a  thread's  address  space, mmemory corruption kill policy determines whether the
       thread received SIGBUS as soon as corruption  is  detected  ("early"),  when  it  accesses
       corrupted memory ("late"), or use system wide default.

       prctl  can optionally be followed by a command. If a command is specified, prctl will exec
       the command with the processor behavior set to as specified by the options. If  a  command
       is  not specified, prctl will fork a new shell unless the command only queried the current
       settings.  The shell started by prctl will be  as  defined  by  the  environment  variable
       SHELL.  If  environment variable SHELL is not defined, shell in the password entry for the
       user will be started. If a shell is not found in the password entry, bash will be started.

   OPTIONS
       -v     Verbose mode. In verbose mode, any new settings are confirmed  with  a  message  on
              stdout.

       --help Print usage information and exit.

       --version
              Print software version and exit.

       -q     Query the current settings for the process options controllable by prctl.

       --unaligned=[silent|signal|always-signal|default]]
              Set unaligned memory access behavior to not log the access (silent), send SIGBUS to
              the process (signal), or  do  the  default  (default).  On  IA-64  architecture  an
              additional  value  always-signal is supported which causes a SIGBUS to be generated
              every time an unaligned access occurs. Refer to the section  titled  "Memory  Datum
              Alignment  and Atomicity" in "Intel IA-64 Architecture Software Developer's Manual:
              Volume 2" for details on  when  an  unaligned  access  would  not  generate  signal
              normally. If a value is not specified after "=", current setting is returned.

       --fpemu=[silent|signal|default]]
              Set  floating  point  assist  fault  behavior  to not log the faulti (silent), send
              SIGFPE to the process (signal), or do the default (default).  If  a  value  is  not
              specified after "=", current setting is returned.

       If an option is specified multiple times, the last one takes effect.

EXAMPLES

       prctl --unaligned=signal
              starts  up  a  shell (as defined by the environment variable SHELL) and sets up any
              process running under this shell to be sent SIGBUS upon an unaligned memory access.

       prctl --unaligned=signal gdb tst
              starts up a gdb session for the program "tst"  with  the  process  set  to  receive
              SIGBUS upon unligned memory access.

       prctl --unaligned=
              displays the current setting for unaligned memory access handling.

       prctl --unaligned= gdb tst
              displays  the  current setting for unaligned memory access handling and starts up a
              gdb session for the program "tst".

NOTES

       prctl works on 2.4.0 and above kernels only.

       --fpemu= option is specific to IPF (Itanium Processor Family, previously known  as  IA-64)
       and  is  supported on kernels 2.4.11 and above. Other architectures and kernels may return
       "Invalid argument" error.

SEE ALSO

       prctl(2)

AUTHOR

       Khalid Aziz <khalid.aziz@oracle.com>

LICENSE

       This software is made available under the GNU General  Public  License  (GPL)  Version  2.
       This software comes with NO WARRANTY.

                                        Process operations                               PRCTL(1)