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]

DESCRIPTION

       prctl  allows  you  to  query  or control certain process behavior.  Supported options are
       handling of unaligned memory accesses and floating point assistance faults by  a  process.
       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 or send SIGBUS to the process. Similarly  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 or send SIGFPE to the offending
       process.

       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@hp.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)