PRCTL(1)PRCTL(1)NAMEprctl - Process operations
SYNOPSISprctl [-v] [-h|--help] [--version] <-q|<options....>> [command]
where <options> are:
--unaligned=[silent|signal|always-signal|default]
--fpemu=[silent|signal|default]
DESCRIPTIONprctl allows you to query or control certain process behavior. Sup‐
ported 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 speci‐
fied, 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 vari‐
able 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-sig‐
nal 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 Architec‐
ture 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 set‐
ting is returned.
If an option is specified multiple times, the last one takes effect.
EXAMPLESprctl --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 SIG‐
BUS 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 han‐
dling.
prctl --unaligned= gdb tst
displays the current setting for unaligned memory access han‐
dling and starts up a gdb session for the program "tst".
NOTESprctl works on 2.4.0 and above kernels only.
--fpemu= option is specific to IPF (Itanium Processor Family, previ‐
ously known as IA-64) and is supported on kernels 2.4.11 and above.
Other architectures and kernels may return "Invalid argument" error.
SEE ALSOprctl(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)
