PRCTL
Section: Linux Programmer's Manual (2)
Updated: 2010-05-13
NAME
prctl - operations on a process
SYNOPSIS
#include <sys/prctl.h>
int prctl(int option, unsigned long arg2, unsigned long arg3,
unsigned long arg4, unsigned long arg5);
DESCRIPTION
prctl()
is called with a first argument describing what to do
(with values defined in <linux/prctl.h>), and further
arguments with a significance depending on the first one.
The first argument can be:
- PR_CAPBSET_READ (since Linux 2.6.25)
-
Return (as the function result) 1 if the capability specified in
arg2
is in the calling thread's capability bounding set,
or 0 if it is not.
(The capability constants are defined in
<linux/capability.h>.)
The capability bounding set dictates
whether the process can receive the capability through a
file's permitted capability set on a subsequent call to
execve(2).
If the capability specified in
arg2
is not valid, then the call fails with the error
EINVAL.
- PR_CAPBSET_DROP (since Linux 2.6.25)
-
If the calling thread has the
CAP_SETPCAP
capability, then drop the capability specified by
arg2
from the calling thread's capability bounding set.
Any children of the calling thread will inherit the newly
reduced bounding set.
The call fails with the error:
EPERM
if the calling thread does not have the
CAP_SETPCAP;
EINVAL
if
arg2
does not represent a valid capability; or
EINVAL
if file capabilities are not enabled in the kernel,
in which case bounding sets are not supported.
- PR_SET_DUMPABLE (since Linux 2.3.20)
-
Set the state of the flag determining whether core dumps are produced
for this process upon delivery of a signal whose default behavior is
to produce a core dump.
(Normally this flag is set for a process by default, but it is cleared
when a set-user-ID or set-group-ID program is executed and also by
various system calls that manipulate process UIDs and GIDs).
In kernels up to and including 2.6.12,
arg2
must be either 0 (process is not dumpable) or 1 (process is dumpable).
Between kernels 2.6.13 and 2.6.17, the value 2 was also permitted,
which caused any binary which normally would not be dumped
to be dumped readable by root only;
for security reasons, this feature has been removed.
(See also the description of
/proc/sys/fs/suid_dumpable
in
proc(5).)
- PR_GET_DUMPABLE (since Linux 2.3.20)
-
Return (as the function result) the current state of the calling
process's dumpable flag.
- PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
-
Set the endian-ness of the calling process to the value given
in arg2, which should be one of the following:
PR_ENDIAN_BIG,
PR_ENDIAN_LITTLE,
or
PR_ENDIAN_PPC_LITTLE
(PowerPC pseudo little endian).
- PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
-
Return the endian-ness of the calling process,
in the location pointed to by
(int *) arg2.
- PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
-
Set floating-point emulation control bits to arg2.
Pass PR_FPEMU_NOPRINT to silently emulate fp operations accesses, or
PR_FPEMU_SIGFPE to not emulate fp operations and send
SIGFPE
instead.
- PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
-
Return floating-point emulation control bits,
in the location pointed to by
(int *) arg2.
- PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
-
Set floating-point exception mode to arg2.
Pass PR_FP_EXC_SW_ENABLE to use FPEXC for FP exception enables,
PR_FP_EXC_DIV for floating-point divide by zero,
PR_FP_EXC_OVF for floating-point overflow,
PR_FP_EXC_UND for floating-point underflow,
PR_FP_EXC_RES for floating-point inexact result,
PR_FP_EXC_INV for floating-point invalid operation,
PR_FP_EXC_DISABLED for FP exceptions disabled,
PR_FP_EXC_NONRECOV for async nonrecoverable exception mode,
PR_FP_EXC_ASYNC for async recoverable exception mode,
PR_FP_EXC_PRECISE for precise exception mode.
- PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
-
Return floating-point exception mode,
in the location pointed to by
(int *) arg2.
- PR_SET_KEEPCAPS (since Linux 2.2.18)
-
Set the state of the thread's "keep capabilities" flag,
which determines whether the threads's permitted
capability set is cleared when a change is made to the threads's user IDs
such that the threads's real UID, effective UID, and saved set-user-ID
all become nonzero when at least one of them previously had the value 0.
By default, the permitted capability set is cleared when such a change is made;
setting the "keep capabilities" flag prevents it from being cleared.
arg2
must be either 0 (permitted capabilities are cleared)
or 1 (permitted capabilities are kept).
(A thread's
effective
capability set is always cleared when such a credential change is made,
regardless of the setting of the "keep capabilities" flag.)
The "keep capabilities" value will be reset to 0 on subsequent calls to
execve(2).
- PR_GET_KEEPCAPS (since Linux 2.2.18)
-
Return (as the function result) the current state of the calling threads's
"keep capabilities" flag.
- PR_SET_NAME (since Linux 2.6.9)
-
Set the process name for the calling process,
using the value in the location pointed to by
(char *) arg2.
The name can be up to 16 bytes long,
and should be null-terminated if it contains fewer bytes.
- PR_GET_NAME (since Linux 2.6.11)
-
Return the process name for the calling process,
in the buffer pointed to by
(char *) arg2.
The buffer should allow space for up to 16 bytes;
the returned string will be null-terminated if it is shorter than that.
- PR_SET_PDEATHSIG (since Linux 2.1.57)
-
Set the parent process death signal
of the calling process to arg2 (either a signal value
in the range 1..maxsig, or 0 to clear).
This is the signal that the calling process will get when its
parent dies.
This value is cleared for the child of a
fork(2).
- PR_GET_PDEATHSIG (since Linux 2.3.15)
-
Return the current value of the parent process death signal,
in the location pointed to by
(int *) arg2.
- PR_SET_SECCOMP (since Linux 2.6.23)
-
Set the secure computing mode for the calling thread.
In the current implementation,
arg2
must be 1.
After the secure computing mode has been set to 1,
the only system calls that the thread is permitted to make are
read(2),
write(2),
_exit(2),
and
sigreturn(2).
Other system calls result in the delivery of a
SIGKILL
signal.
Secure computing mode is useful for number-crunching applications
that may need to execute untrusted byte code,
perhaps obtained by reading from a pipe or socket.
This operation is only available
if the kernel is configured with CONFIG_SECCOMP enabled.
- PR_GET_SECCOMP (since Linux 2.6.23)
-
Return the secure computing mode of the calling thread.
Not very useful for the current implementation (mode equals 1),
but may be useful for other possible future modes:
if the caller is not in secure computing mode, this operation returns 0;
if the caller is in secure computing mode, then the
prctl()
call will cause a
SIGKILL
signal to be sent to the process.
This operation is only available
if the kernel is configured with CONFIG_SECCOMP enabled.
- PR_SET_SECUREBITS (since Linux 2.6.26)
-
Set the "securebits" flags of the calling thread to the value supplied in
arg2.
See
capabilities(7).
- PR_GET_SECUREBITS (since Linux 2.6.26)
-
Return (as the function result)
the "securebits" flags of the calling thread.
See
capabilities(7).
- PR_SET_TIMING (since Linux 2.6.0-test4)
-
Set whether to use (normal, traditional) statistical process timing or
accurate timestamp based process timing, by passing
PR_TIMING_STATISTICAL
or
PR_TIMING_TIMESTAMP
to arg2.
PR_TIMING_TIMESTAMP
is not currently implemented
(attempting to set this mode will yield the error
EINVAL).
- PR_GET_TIMING (since Linux 2.6.0-test4)
-
Return (as the function result) which process timing method is currently
in use.
- PR_SET_TSC (since Linux 2.6.26, x86 only)
-
Set the state of the flag determining whether the timestamp counter
can be read by the process.
Pass
PR_TSC_ENABLE
to
arg2
to allow it to be read, or
PR_TSC_SIGSEGV
to generate a
SIGSEGV
when the process tries to read the timestamp counter.
- PR_GET_TSC (since Linux 2.6.26, x86 only)
-
Return the state of the flag determining whether the timestamp counter
can be read,
in the location pointed to by
(int *) arg2.
- PR_SET_UNALIGN
-
(Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22)
Set unaligned access control bits to arg2.
Pass
PR_UNALIGN_NOPRINT to silently fix up unaligned user accesses,
or PR_UNALIGN_SIGBUS to generate
SIGBUS
on unaligned user access.
- PR_GET_UNALIGN
-
(see
PR_SET_UNALIGN
for information on versions and architectures)
Return unaligned access control bits, in the location pointed to by
(int *) arg2.
- PR_MCE_KILL (since Linux 2.6.32)
-
Set the machine check memory corruption kill policy for the current thread.
If
arg2
is
PR_MCE_KILL_CLEAR,
clear the thread memory corruption kill policy and use the system-wide default.
(The system-wide default is defined by
/proc/sys/vm/memory_failure_early_kill;
see
proc(5).)
If
arg2
is
PR_MCE_KILL_SET,
use a thread-specific memory corruption kill policy.
In this case,
arg3
defines whether the policy is
early kill
(PR_MCE_KILL_EARLY),
late kill
(PR_MCE_KILL_LATE),
or the system-wide default
(PR_MCE_KILL_DEFAULT).
Early kill means that the task receives a
SIGBUS
signal as soon as hardware memory corruption is detected inside
its address space.
In late kill mode, the process is only killed when it accesses a corrupted page.
See
sigaction(2)
for more information on the
SIGBUS
signal.
The policy is inherited by children.
The remaining unused
prctl()
arguments must be zero for future compatibility.
- PR_MCE_KILL_GET (since Linux 2.6.32)
-
Return the current per-process machine check kill policy.
All unused
prctl()
arguments must be zero.
RETURN VALUE
On success,
PR_GET_DUMPABLE,
PR_GET_KEEPCAPS,
PR_CAPBSET_READ,
PR_GET_TIMING,
PR_GET_SECUREBITS,
PR_MCE_KILL_GET,
and (if it returns)
PR_GET_SECCOMP
return the nonnegative values described above.
All other
option
values return 0 on success.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- EFAULT
-
arg2
is an invalid address.
- EINVAL
-
The value of
option
is not recognized.
- EINVAL
-
option
is
PR_MCE_KILL
or
PR_MCE_KILL_GET,
and unused
prctl()
arguments were not specified as zero.
- EINVAL
-
arg2
is not valid value for this
option.
- EINVAL
-
option
is
PR_SET_SECCOMP
or
PR_SET_SECCOMP,
and the kernel was not configured with
CONFIG_SECCOMP.
- EPERM
-
option
is
PR_SET_SECUREBITS,
and the caller does not have the
CAP_SETPCAP
capability,
or tried to unset a "locked" flag,
or tried to set a flag whose corresponding locked flag was set
(see
capabilities(7)).
- EPERM
-
option
is
PR_SET_KEEPCAPS,
and the callers's
SECURE_KEEP_CAPS_LOCKED
flag is set
(see
capabilities(7)).
- EPERM
-
option
is
PR_CAPBSET_DROP,
and the caller does not have the
CAP_SETPCAP
capability.
VERSIONS
The
prctl()
system call was introduced in Linux 2.1.57.
CONFORMING TO
This call is Linux-specific.
IRIX has a
prctl()
system call (also introduced in Linux 2.1.44
as irix_prctl on the MIPS architecture),
with prototype
ptrdiff_t prctl(int option, int arg2, int arg3);
and options to get the maximum number of processes per user,
get the maximum number of processors the calling process can use,
find out whether a specified process is currently blocked,
get or set the maximum stack size, etc.
SEE ALSO
signal(2),
core(5)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
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Time: 07:34:57 GMT, March 26, 2013