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)