PRCTL(2)

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 parameters with a significance depending on the first one. The first argument can be:

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 upon a fork(2).

PR_GET_PDEATHSIG
    (Since Linux 2.3.15) Read the current value of the parent process death signal into the (int *) arg2.

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_KEEPCAPS
    (Since Linux 2.2.18) Set the state of the process's "keep capabilities" flag, which determines whether the process's effective and permitted capability sets are cleared when a change is made to the process's user IDs such that the process's real UID, effective UID, and saved set-user-ID all become non-zero when at least one of them previously had the value 0. (By default, these credential sets are cleared). arg2 must be either 0 (capabilities are cleared) or 1 (capabilities are kept).

PR_GET_KEEPCAPS
    (Since Linux 2.2.18) Return (as the function result) the current state of the calling process's "keep capabilities" flag.

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_GET_TIMING
    (Since Linux 2.6.0-test4) Return (as the function result) which process timing method is currently in use.

PR_SET_NAME
    (Since Linux 2.6.9) Set the process name for the calling process to arg2.

PR_GET_NAME
    (Since Linux 2.6.11) Get the process name for the calling process from arg2.

PR_GET_ENDIAN
    (Since Linux 2.6.18, PowerPC only) Return the endian-ness of the calling process.

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_SET_UNALIGN
    (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15; PowerPC, since Linux 2.6.18) 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) Get unaligned access control bits from 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) Get floating-point emulation control bits from 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 non-recoverable 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) Get floating-point exception mode from arg2.

RETURN VALUE
PR_GET_DUMPABLE and PR_GET_KEEPCAPS return 0 or 1 on success. All other option values return 0 on success. On error, -1 is returned, and errno is set appropriately.

ERRORS

EINVAL
    The value of option is not recognized, or it is PR_SET_PDEATHSIG and arg2 is not zero or a signal number.

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)