prctl - operations on a process


 #include <sys/prctl.h>
 int prctl(int option, unsigned long arg2, unsigned long arg3,
           unsigned long arg4, unsigned long arg5);


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:
(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).
(Since Linux 2.3.15) Read the current value of the parent process death signal into the (int *) arg2.
(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).)
(Since Linux 2.3.20) Return (as the function result) the current state of the calling process's dumpable flag.
(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).
(Since Linux 2.2.18) Return (as the function result) the current state of the calling process's "keep capabilities" flag.
(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.
(Since Linux 2.6.0-test4) Return (as the function result) which process timing method is currently in use.
(Since Linux 2.6.9) Set the process name for the calling process to arg2.
(Since Linux 2.6.11) Get the process name for the calling process from arg2.
(Since Linux 2.6.18, PowerPC only) Return the endian-ness of the calling process.
(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).
(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.
(see PR_SET_UNALIGN for information on versions and architectures) Get unaligned access control bits from arg2.
(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.
(Since Linux 2.4.18, 2.5.9, only on ia64) Get floating-point emulation control bits from arg2.
(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.
(Since Linux 2.4.21, 2.5.32, only on PowerPC) Get floating-point exception mode from arg2.


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.


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


The prctl() system call was introduced in Linux 2.1.57.


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.


signal(2), core(5)