.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH prctl 2 2025-06-11 "Linux man-pages (unreleased)"
.SH NAME
prctl
\-
operations on a process or thread
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/prctl.h>" "  /* Definition of " PR_* " constants */"
.B #include <sys/prctl.h>
.P
.BI "int prctl(int " op ", ...);"
.fi
.SH DESCRIPTION
.BR prctl ()
manipulates various aspects of the behavior
of the calling thread or process.
.P
.BR prctl ()
is called with a first argument describing what to do,
and further arguments
with a significance depending on the first one.
The first argument can be:
.\"
.TP
.B PR_CAP_AMBIENT
.TQ
.B PR_CAPBSET_READ
.TQ
.B PR_CAPBSET_DROP
.TQ
.B PR_SET_CHILD_SUBREAPER
.TQ
.B PR_GET_CHILD_SUBREAPER
.TQ
.B PR_SET_DUMPABLE
.TQ
.B PR_GET_DUMPABLE
.TQ
.B PR_SET_ENDIAN
.TQ
.B PR_GET_ENDIAN
.TQ
.B PR_SET_FP_MODE
.TQ
.B PR_GET_FP_MODE
.TQ
.B PR_SET_FPEMU
.TQ
.B PR_GET_FPEMU
.TQ
.B PR_SET_FPEXC
.TQ
.B PR_GET_FPEXC
.TQ
.B PR_SET_IO_FLUSHER
.TQ
.B PR_GET_IO_FLUSHER
.TQ
.B PR_SET_KEEPCAPS
.TQ
.B PR_GET_KEEPCAPS
.TQ
.B PR_MCE_KILL
.TQ
.B PR_MCE_KILL_GET
.TQ
.B PR_SET_MM
.TQ
.B PR_SET_VMA
.TQ
.B PR_MPX_ENABLE_MANAGEMENT
.TQ
.B PR_MPX_DISABLE_MANAGEMENT
.TQ
.B PR_SET_NAME
.TQ
.B PR_GET_NAME
.TQ
.B PR_SET_NO_NEW_PRIVS
.TQ
.B PR_GET_NO_NEW_PRIVS
.TQ
.B PR_PAC_RESET_KEYS
.TQ
.B PR_SET_PDEATHSIG
.TQ
.B PR_GET_PDEATHSIG
.TQ
.B PR_SET_PTRACER
.TQ
.B PR_SET_SECCOMP
.TQ
.B PR_GET_SECCOMP
.TQ
.B PR_SET_SECUREBITS
.TQ
.B PR_GET_SECUREBITS
.TQ
.B PR_GET_SPECULATION_CTRL
.TQ
.B PR_SET_SPECULATION_CTRL
.TQ
.B PR_SVE_SET_VL
.TQ
.B PR_SVE_GET_VL
.TQ
.B PR_SET_SYSCALL_USER_DISPATCH
.TQ
.B PR_SET_TAGGED_ADDR_CTRL
.TQ
.B PR_GET_TAGGED_ADDR_CTRL
.TQ
.B PR_TASK_PERF_EVENTS_DISABLE
.TQ
.B PR_TASK_PERF_EVENTS_ENABLE
.TQ
.B PR_SET_THP_DISABLE
.TQ
.B PR_GET_THP_DISABLE
.TQ
.B PR_GET_TID_ADDRESS
.TQ
.B PR_SET_TIMERSLACK
.TQ
.B PR_GET_TIMERSLACK
.TQ
.B PR_SET_TIMING
.TQ
.B PR_GET_TIMING
.TQ
.B PR_SET_TSC
.TQ
.B PR_GET_TSC
.TQ
.B PR_SET_UNALIGN
.TQ
.B PR_GET_UNALIGN
.TQ
.B PR_GET_AUXV
.TQ
.B PR_SET_MDWE
.TQ
.B PR_GET_MDWE
.TQ
.B PR_RISCV_SET_ICACHE_FLUSH_CTX
.TQ
.B PR_FUTEX_HASH
.SH RETURN VALUE
On success,
a nonnegative value is returned.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
The value of
.I op
is not recognized,
or not supported on this system.
.TP
.B EINVAL
An unused argument is nonzero.
.SH VERSIONS
IRIX has a
.BR prctl ()
system call (also introduced in Linux 2.1.44
as irix_prctl on the MIPS architecture),
with prototype
.P
.in +4n
.EX
.BI "ptrdiff_t prctl(int " op ", int " arg2 ", int " arg3 );
.EE
.in
.P
and operations 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, and so on.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.1.57,
glibc 2.0.6
.SH CAVEATS
The prototype of the libc wrapper uses a variadic argument list.
This makes it necessary to pass the arguments with the right width.
When passing numeric constants, such as 0,
use a suffix:
.BR 0L .
.P
Careless use of some
.BR prctl ()
operations can confuse the user-space run-time environment,
so these operations should be used with care.
.SH SEE ALSO
.BR signal (2),
.BR PR_CAP_AMBIENT (2const),
.BR PR_CAPBSET_READ (2const),
.BR PR_CAPBSET_DROP (2const),
.BR PR_SET_CHILD_SUBREAPER (2const),
.BR PR_GET_CHILD_SUBREAPER (2const),
.BR PR_SET_DUMPABLE (2const),
.BR PR_GET_DUMPABLE (2const),
.BR PR_SET_ENDIAN (2const),
.BR PR_GET_ENDIAN (2const),
.BR PR_SET_FP_MODE (2const),
.BR PR_GET_FP_MODE (2const),
.BR PR_SET_FPEMU (2const),
.BR PR_GET_FPEMU (2const),
.BR PR_SET_FPEXC (2const),
.BR PR_GET_FPEXC (2const),
.BR PR_SET_IO_FLUSHER (2const),
.BR PR_GET_IO_FLUSHER (2const),
.BR PR_SET_KEEPCAPS (2const),
.BR PR_GET_KEEPCAPS (2const),
.BR PR_MCE_KILL (2const),
.BR PR_MCE_KILL_GET (2const),
.BR PR_SET_MM (2const),
.BR PR_SET_VMA (2const),
.BR PR_MPX_ENABLE_MANAGEMENT (2const),
.BR PR_MPX_DISABLE_MANAGEMENT (2const),
.BR PR_SET_NAME (2const),
.BR PR_GET_NAME (2const),
.BR PR_SET_NO_NEW_PRIVS (2const),
.BR PR_GET_NO_NEW_PRIVS (2const),
.BR PR_PAC_RESET_KEYS (2const),
.BR PR_SET_PDEATHSIG (2const),
.BR PR_GET_PDEATHSIG (2const),
.BR PR_SET_PTRACER (2const),
.BR PR_SET_SECCOMP (2const),
.BR PR_GET_SECCOMP (2const),
.BR PR_SET_SECUREBITS (2const),
.BR PR_GET_SECUREBITS (2const),
.BR PR_SET_SPECULATION_CTRL (2const),
.BR PR_GET_SPECULATION_CTRL (2const),
.BR PR_SVE_SET_VL (2const),
.BR PR_SVE_GET_VL (2const),
.BR PR_SET_SYSCALL_USER_DISPATCH (2const),
.BR PR_SET_TAGGED_ADDR_CTRL (2const),
.BR PR_GET_TAGGED_ADDR_CTRL (2const),
.BR PR_TASK_PERF_EVENTS_DISABLE (2const),
.BR PR_TASK_PERF_EVENTS_ENABLE (2const),
.BR PR_SET_THP_DISABLE (2const),
.BR PR_GET_THP_DISABLE (2const),
.BR PR_GET_TID_ADDRESS (2const),
.BR PR_SET_TIMERSLACK (2const),
.BR PR_GET_TIMERSLACK (2const),
.BR PR_SET_TIMING (2const),
.BR PR_GET_TIMING (2const),
.BR PR_SET_TSC (2const),
.BR PR_GET_TSC (2const),
.BR PR_SET_UNALIGN (2const),
.BR PR_GET_UNALIGN (2const),
.BR PR_GET_AUXV (2const),
.BR PR_SET_MDWE (2const),
.BR PR_GET_MDWE (2const),
.BR PR_RISCV_SET_ICACHE_FLUSH_CTX (2const),
.BR PR_FUTEX_HASH (2const),
.BR core (5)