PRCTL(2)                  (2020-08-13)                   PRCTL(2)

     NAME
          prctl - operations on a process or thread

     SYNOPSIS
          #include <sys/prctl.h>

          int prctl(int option, unsigned long arg2, unsigned long arg3
                    unsigned long arg4, unsigned long arg5);

     DESCRIPTION
          prctl() manipulates various aspects of the behavior of the
          calling thread or process.

          Note that careless use of some prctl() operations can con-
          fuse the user-space run-time environment, so these opera-
          tions should be used with care.

          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_CAP_AMBIENT (since Linux 4.3)
               Reads or changes the ambient capability set of the
               calling thread, according to the value of arg2, which
               must be one of the following:

               PR_CAP_AMBIENT_RAISE
                    The capability specified in arg3 is added to the
                    ambient set.  The specified capability must
                    already be present in both the permitted and the
                    inheritable sets of the process.  This operation
                    is not permitted if the
                    SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.

               PR_CAP_AMBIENT_LOWER
                    The capability specified in arg3 is removed from
                    the ambient set.

               PR_CAP_AMBIENT_IS_SET
                    The prctl() call returns 1 if the capability in
                    arg3 is in the ambient set and 0 if it is not.

               PR_CAP_AMBIENT_CLEAR_ALL
                    All capabilities will be removed from the ambient
                    set.  This operation requires setting arg3 to
                    zero.

               In all of the above operations, arg4 and arg5 must be
               specified as 0.

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               Higher-level interfaces layered on top of the above
               operations are provided in the libcap(3) library in the
               form of cap_get_ambient(3), cap_set_ambient(3), and
               cap_reset_ambient(3).

          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 con-
               stants are defined in <linux/capability.h>.) The capa-
               bility bounding set dictates whether the process can
               receive the capability through a file's permitted capa-
               bility 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.

               A higher-level interface layered on top of this opera-
               tion is provided in the libcap(3) library in the form
               of cap_get_bound(3).

          PR_CAPBSET_DROP (since Linux 2.6.25)
               If the calling thread has the CAP_SETPCAP capability
               within its user namespace, 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.

               A higher-level interface layered on top of this opera-
               tion is provided in the libcap(3) library in the form
               of cap_drop_bound(3).

          PR_SET_CHILD_SUBREAPER (since Linux 3.4)
               If arg2 is nonzero, set the "child subreaper" attribute
               of the calling process; if arg2 is zero, unset the
               attribute.

               A subreaper fulfills the role of init(1) for its
               descendant processes.  When a process becomes orphaned
               (i.e., its immediate parent terminates), then that pro-
               cess will be reparented to the nearest still living
               ancestor subreaper.  Subsequently, calls to getppid(2)
               in the orphaned process will now return the PID of the
               subreaper process, and when the orphan terminates, it
               is the subreaper process that will receive a SIGCHLD
               signal and will be able to wait(2) on the process to

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               discover its termination status.

               The setting of the "child subreaper" attribute is not
               inherited by children created by fork(2) and clone(2).
               The setting is preserved across execve(2).

               Establishing a subreaper process is useful in session
               management frameworks where a hierarchical group of
               processes is managed by a subreaper process that needs
               to be informed when one of the processes-for example, a
               double-forked daemon-terminates (perhaps so that it can
               restart that process).  Some init(1) frameworks (e.g.,
               systemd(1)) employ a subreaper process for similar rea-
               sons.

          PR_GET_CHILD_SUBREAPER (since Linux 3.4)
               Return the "child subreaper" setting of the caller, in
               the location pointed to by (int *) arg2.

          PR_SET_DUMPABLE (since Linux 2.3.20)
               Set the state of the "dumpable" attribute, which deter-
               mines whether core dumps are produced for the calling
               process upon delivery of a signal whose default behav-
               ior is to produce a core dump.

               In kernels up to and including 2.6.12, arg2 must be
               either 0 (SUID_DUMP_DISABLE, process is not dumpable)
               or 1 (SUID_DUMP_USER, process is dumpable).  Between
               kernels 2.6.13 and 2.6.17, the value 2 was also permit-
               ted, which caused any binary which normally would not
               be dumped to be dumped readable by root only; for secu-
               rity reasons, this feature has been removed.  (See also
               the description of /proc/sys/fs/:suid_dumpable in
               proc(5).)

               Normally, the "dumpable" attribute is set to 1.  How-
               ever, it is reset to the current value contained in the
               file /proc/sys/fs/:suid_dumpable (which by default has
               the value 0), in the following circumstances:

               *  The process's effective user or group ID is changed.

               *  The process's filesystem user or group ID is changed
                  (see credentials(7)).

               *  The process executes (execve(2)) a set-user-ID or
                  set-group-ID program, resulting in a change of
                  either the effective user ID or the effective group
                  ID.

               *  The process executes (execve(2)) a program that has
                  file capabilities (see capabilities(7)), but only if

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                  the permitted capabilities gained exceed those
                  already permitted for the process.

               Processes that are not dumpable can not be attached via
               ptrace(2) PTRACE_ATTACH; see ptrace(2) for further
               details.

               If a process is not dumpable, the ownership of files in
               the process's /proc/[pid] directory is affected as
               described 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 attribute.

          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_FP_MODE (since Linux 4.0, only on MIPS)
               On the MIPS architecture, user-space code can be built
               using an ABI which permits linking with code that has
               more restrictive floating-point (FP) requirements.  For
               example, user-space code may be built to target the O32
               FPXX ABI and linked with code built for either one of
               the more restrictive FP32 or FP64 ABIs.  When more
               restrictive code is linked in, the overall requirement
               for the process is to use the more restrictive
               floating-point mode.

               Because the kernel has no means of knowing in advance
               which mode the process should be executed in, and
               because these restrictions can change over the lifetime
               of the process, the PR_SET_FP_MODE operation is pro-
               vided to allow control of the floating-point mode from
               user space.

               The (unsigned int) arg2 argument is a bit mask describ-
               ing the floating-point mode used:

               PR_FP_MODE_FR
                    When this bit is unset (so called FR=0 or FR0
                    mode), the 32 floating-point registers are 32 bits
                    wide, and 64-bit registers are represented as a
                    pair of registers (even- and odd- numbered, with
                    the even-numbered register containing the lower 32

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                    bits, and the odd-numbered register containing the
                    higher 32 bits).

                    When this bit is set (on supported hardware), the
                    32 floating-point registers are 64 bits wide (so
                    called FR=1 or FR1 mode).  Note that modern MIPS
                    implementations (MIPS R6 and newer) support FR=1
                    mode only.

                    Applications that use the O32 FP32 ABI can operate
                    only when this bit is unset (FR=0; or they can be
                    used with FRE enabled, see below).  Applications
                    that use the O32 FP64 ABI (and the O32 FP64A ABI,
                    which exists to provide the ability to operate
                    with existing FP32 code; see below) can operate
                    only when this bit is set (FR=1).  Applications
                    that use the O32 FPXX ABI can operate with either
                    FR=0 or FR=1.

               PR_FP_MODE_FRE
                    Enable emulation of 32-bit floating-point mode.
                    When this mode is enabled, it emulates 32-bit
                    floating-point operations by raising a reserved-
                    instruction exception on every instruction that
                    uses 32-bit formats and the kernel then handles
                    the instruction in software.  (The problem lies in
                    the discrepancy of handling odd-numbered registers
                    which are the high 32 bits of 64-bit registers
                    with even numbers in FR=0 mode and the lower 32-
                    bit parts of odd-numbered 64-bit registers in FR=1
                    mode.)  Enabling this bit is necessary when code
                    with the O32 FP32 ABI should operate with code
                    with compatible the O32 FPXX or O32 FP64A ABIs
                    (which require FR=1 FPU mode) or when it is exe-
                    cuted on newer hardware (MIPS R6 onwards) which
                    lacks FR=0 mode support when a binary with the
                    FP32 ABI is used.

                    Note that this mode makes sense only when the FPU
                    is in 64-bit mode (FR=1).

                    Note that the use of emulation inherently has a
                    significant performance hit and should be avoided
                    if possible.

               In the N32/N64 ABI, 64-bit floating-point mode is
               always used, so FPU emulation is not required and the
               FPU always operates in FR=1 mode.

               This option is mainly intended for use by the dynamic
               linker (ld.so(8)).

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               The arguments arg3, arg4, and arg5 are ignored.

          PR_GET_FP_MODE (since Linux 4.0, only on MIPS)
               Return (as the function result) the current floating-
               point mode (see the description of PR_SET_FP_MODE for
               details).

               On success, the call returns a bit mask which repre-
               sents the current floating-point mode.

               The arguments arg2, arg3, arg4, and arg5 are ignored.

          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 floating-
               point operation accesses, or PR_FPEMU_SIGFPE to not
               emulate floating-point 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_IO_FLUSHER (since Linux 5.6)
               If a user process is involved in the block layer or
               filesystem I/O path, and can allocate memory while pro-
               cessing I/O requests it must set arg2 to 1.  This will
               put the process in the IO_FLUSHER state, which allows
               it special treatment to make progress when allocating
               memory.  If arg2 is 0, the process will clear the
               IO_FLUSHER state, and the default behavior will be
               used.

               The calling process must have the CAP_SYS_RESOURCE
               capability.

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               arg3, arg4, and arg5 must be zero.

               The IO_FLUSHER state is inherited by a child process
               created via fork(2) and is preserved across execve(2).

               Examples of IO_FLUSHER applications are FUSE daemons,
               SCSI device emulation daemons, and daemons that perform
               error handling like multipath path recovery applica-
               tions.

          PR_GET_IO_FLUSHER (Since Linux 5.6)
               Return (as the function result) the IO_FLUSHER state of
               the caller.  A value of 1 indicates that the caller is
               in the IO_FLUSHER state; 0 indicates that the caller is
               not in the IO_FLUSHER state.

               The calling process must have the CAP_SYS_RESOURCE
               capability.

               arg2, arg3, arg4, and arg5 must be zero.

          PR_SET_KEEPCAPS (since Linux 2.2.18)
               Set the state of the calling thread's "keep capabili-
               ties" flag.  The effect of this flag is described in
               capabilities(7).  arg2 must be either 0 (clear the
               flag) or 1 (set the 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 thread's "keep capabilities" flag.  See
               capabilities(7) for a description of this flag.

          PR_MCE_KILL (since Linux 2.6.32)
               Set the machine check memory corruption kill policy for
               the calling 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 thread receives a SIGBUS signal as
               soon as hardware memory corruption is detected inside
               its address space.  In late kill mode, the process is
               killed only 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

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               compatibility.

          PR_MCE_KILL_GET (since Linux 2.6.32)
               Return (as the function result) the current per-process
               machine check kill policy.  All unused prctl() argu-
               ments must be zero.

          PR_SET_MM (since Linux 3.3)
               Modify certain kernel memory map descriptor fields of
               the calling process.  Usually these fields are set by
               the kernel and dynamic loader (see ld.so(8) for more
               information) and a regular application should not use
               this feature.  However, there are cases, such as self-
               modifying programs, where a program might find it use-
               ful to change its own memory map.

               The calling process must have the CAP_SYS_RESOURCE
               capability.  The value in arg2 is one of the options
               below, while arg3 provides a new value for the option.
               The arg4 and arg5 arguments must be zero if unused.

               Before Linux 3.10, this feature is available only if
               the kernel is built with the CONFIG_CHECKPOINT_RESTORE
               option enabled.

               PR_SET_MM_START_CODE
                    Set the address above which the program text can
                    run.  The corresponding memory area must be read-
                    able and executable, but not writable or shareable
                    (see mprotect(2) and mmap(2) for more informa-
                    tion).

               PR_SET_MM_END_CODE
                    Set the address below which the program text can
                    run.  The corresponding memory area must be read-
                    able and executable, but not writable or share-
                    able.

               PR_SET_MM_START_DATA
                    Set the address above which initialized and unini-
                    tialized (bss) data are placed.  The corresponding
                    memory area must be readable and writable, but not
                    executable or shareable.

               PR_SET_MM_END_DATA
                    Set the address below which initialized and unini-
                    tialized (bss) data are placed.  The corresponding
                    memory area must be readable and writable, but not
                    executable or shareable.

               PR_SET_MM_START_STACK
                    Set the start address of the stack.  The

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                    corresponding memory area must be readable and
                    writable.

               PR_SET_MM_START_BRK
                    Set the address above which the program heap can
                    be expanded with brk(2) call.  The address must be
                    greater than the ending address of the current
                    program data segment.  In addition, the combined
                    size of the resulting heap and the size of the
                    data segment can't exceed the RLIMIT_DATA resource
                    limit (see setrlimit(2)).

               PR_SET_MM_BRK
                    Set the current brk(2) value.  The requirements
                    for the address are the same as for the
                    PR_SET_MM_START_BRK option.

               The following options are available since Linux 3.5.

               PR_SET_MM_ARG_START
                    Set the address above which the program command
                    line is placed.

               PR_SET_MM_ARG_END
                    Set the address below which the program command
                    line is placed.

               PR_SET_MM_ENV_START
                    Set the address above which the program environ-
                    ment is placed.

               PR_SET_MM_ENV_END
                    Set the address below which the program environ-
                    ment is placed.

                    The address passed with PR_SET_MM_ARG_START,
                    PR_SET_MM_ARG_END, PR_SET_MM_ENV_START, and
                    PR_SET_MM_ENV_END should belong to a process stack
                    area.  Thus, the corresponding memory area must be
                    readable, writable, and (depending on the kernel
                    configuration) have the MAP_GROWSDOWN attribute
                    set (see mmap(2)).

               PR_SET_MM_AUXV
                    Set a new auxiliary vector.  The arg3 argument
                    should provide the address of the vector.  The
                    arg4 is the size of the vector.

               PR_SET_MM_EXE_FILE
                    Supersede the /proc/pid/exe symbolic link with a
                    new one pointing to a new executable file identi-
                    fied by the file descriptor provided in arg3

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                    argument.  The file descriptor should be obtained
                    with a regular open(2) call.

                    To change the symbolic link, one needs to unmap
                    all existing executable memory areas, including
                    those created by the kernel itself (for example
                    the kernel usually creates at least one executable
                    memory area for the ELF .text section).

                    In Linux 4.9 and earlier, the PR_SET_MM_EXE_FILE
                    operation can be performed only once in a
                    process's lifetime; attempting to perform the
                    operation a second time results in the error
                    EPERM.  This restriction was enforced for security
                    reasons that were subsequently deemed specious,
                    and the restriction was removed in Linux 4.10
                    because some user-space applications needed to
                    perform this operation more than once.

               The following options are available since Linux 3.18.

               PR_SET_MM_MAP
                    Provides one-shot access to all the addresses by
                    passing in a struct prctl_mm_map (as defined in
                    <linux/prctl.h>).  The arg4 argument should pro-
                    vide the size of the struct.

                    This feature is available only if the kernel is
                    built with the CONFIG_CHECKPOINT_RESTORE option
                    enabled.

               PR_SET_MM_MAP_SIZE
                    Returns the size of the struct prctl_mm_map the
                    kernel expects.  This allows user space to find a
                    compatible struct.  The arg4 argument should be a
                    pointer to an unsigned int.

                    This feature is available only if the kernel is
                    built with the CONFIG_CHECKPOINT_RESTORE option
                    enabled.

     3.19, removed in Linux 5.4; only on x86)
          PR_MPX_ENABLE_MANAGEMENT, PR_MPX_DISABLE_MANAGEMENT (since Linux
               Enable or disable kernel management of Memory Protec-
               tion eXtensions (MPX) bounds tables.  The arg2, arg3,
               arg4, and arg5 arguments must be zero.

               MPX is a hardware-assisted mechanism for performing
               bounds checking on pointers.  It consists of a set of
               registers storing bounds information and a set of spe-
               cial instruction prefixes that tell the CPU on which
               instructions it should do bounds enforcement.  There is

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               a limited number of these registers and when there are
               more pointers than registers, their contents must be
               "spilled" into a set of tables.  These tables are
               called "bounds tables" and the MPX prctl() operations
               control whether the kernel manages their allocation and
               freeing.

               When management is enabled, the kernel will take over
               allocation and freeing of the bounds tables.  It does
               this by trapping the #BR exceptions that result at
               first use of missing bounds tables and instead of
               delivering the exception to user space, it allocates
               the table and populates the bounds directory with the
               location of the new table.  For freeing, the kernel
               checks to see if bounds tables are present for memory
               which is not allocated, and frees them if so.

               Before enabling MPX management using
               PR_MPX_ENABLE_MANAGEMENT, the application must first
               have allocated a user-space buffer for the bounds
               directory and placed the location of that directory in
               the bndcfgu register.

               These calls fail if the CPU or kernel does not support
               MPX.  Kernel support for MPX is enabled via the
               CONFIG_X86_INTEL_MPX configuration option.  You can
               check whether the CPU supports MPX by looking for the
               mpx CPUID bit, like with the following command:

                   cat /proc/cpuinfo | grep aq mpx aq

               A thread may not switch in or out of long (64-bit) mode
               while MPX is enabled.

               All threads in a process are affected by these calls.

               The child of a fork(2) inherits the state of MPX man-
               agement.  During execve(2), MPX management is reset to
               a state as if PR_MPX_DISABLE_MANAGEMENT had been
               called.

               For further information on Intel MPX, see the kernel
               source file Documentation/x86/intel_mpx.txt.

               Due to a lack of toolchain support,
               PR_MPX_ENABLE_MANAGEMENT and PR_MPX_DISABLE_MANAGEMENT
               are not supported in Linux 5.4 and later.

          PR_SET_NAME (since Linux 2.6.9)
               Set the name of the calling thread, using the value in
               the location pointed to by (char *) arg2. The name can
               be up to 16 bytes long, including the terminating null

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               byte.  (If the length of the string, including the ter-
               minating null byte, exceeds 16 bytes, the string is
               silently truncated.)  This is the same attribute that
               can be set via pthread_setname_np(3) and retrieved
               using pthread_getname_np(3).  The attribute is likewise
               accessible via /proc/self/task/[tid]/comm (see
               proc(5)), where [tid] is the thread ID of the calling
               thread, as returned by gettid(2).

          PR_GET_NAME (since Linux 2.6.11)
               Return the name of the calling thread, 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.

          PR_SET_NO_NEW_PRIVS (since Linux 3.5)
               Set the calling thread's no_new_privs attribute to the
               value in arg2. With no_new_privs set to 1, execve(2)
               promises not to grant privileges to do anything that
               could not have been done without the execve(2) call
               (for example, rendering the set-user-ID and set-group-
               ID mode bits, and file capabilities non-functional).
               Once set, the no_new_privs attribute cannot be unset.
               The setting of this attribute is inherited by children
               created by fork(2) and clone(2), and preserved across
               execve(2).

               Since Linux 4.10, the value of a thread's no_new_privs
               attribute can be viewed via the NoNewPrivs field in the
               /proc/[pid]/status file.

               For more information, see the kernel source file
               Documentation/userspace-api/no_new_privs.rst (or
               Documentation/prctl/no_new_privs.txt before Linux
               4.13).  See also seccomp(2).

          PR_GET_NO_NEW_PRIVS (since Linux 3.5)
               Return (as the function result) the value of the
               no_new_privs attribute for the calling thread.  A value
               of 0 indicates the regular execve(2) behavior.  A value
               of 1 indicates execve(2) will operate in the
               privilege-restricting mode described above.

          PR_PAC_RESET_KEYS (since Linux 5.0, only on arm64)
               Securely reset the thread's pointer authentication keys
               to fresh random values generated by the kernel.

               The set of keys to be reset is specified by arg2, which
               must be a logical OR of zero or more of the following:

               PR_PAC_APIAKEY
                    instruction authentication key A

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               PR_PAC_APIBKEY
                    instruction authentication key B

               PR_PAC_APDAKEY
                    data authentication key A

               PR_PAC_APDBKEY
                    data authentication key B

               PR_PAC_APGAKEY
                    generic authentication lqArq key.

                    (Yes folks, there really is no generic B key.)

               As a special case, if arg2 is zero, then all the keys
               are reset.  Since new keys could be added in future,
               this is the recommended way to completely wipe the
               existing keys when establishing a clean execution con-
               text.  Note that there is no need to use
               PR_PAC_RESET_KEYS in preparation for calling execve(2),
               since execve(2) resets all the pointer authentication
               keys.

               The remaining arguments arg3, arg4, and arg5 must all
               be zero.

               If the arguments are invalid, and in particular if arg2
               contains set bits that are unrecognized or that corre-
               spond to a key not available on this platform, then the
               call fails with error EINVAL.

               Warning: Because the compiler or run-time environment
               may be using some or all of the keys, a successful
               PR_PAC_RESET_KEYS may crash the calling process.  The
               conditions for using it safely are complex and system-
               dependent.  Don't use it unless you know what you are
               doing.

               For more information, see the kernel source file
               Documentation/arm64/pointer-authentication.rst (or
               Documentation/arm64/pointer-authentication.txt before
               Linux 5.3).

          PR_SET_PDEATHSIG (since Linux 2.1.57)
               Set the parent-death signal of the calling process to
               arg2 (either a signal value in the range 1..NSIG-1, or
               0 to clear).  This is the signal that the calling pro-
               cess will get when its parent dies.

               Warning: the "parent" in this case is considered to be
               the thread that created this process.  In other words,
               the signal will be sent when that thread terminates

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               (via, for example, pthread_exit(3)), rather than after
               all of the threads in the parent process terminate.

               The parent-death signal is sent upon subsequent termi-
               nation of the parent thread and also upon termination
               of each subreaper process (see the description of
               PR_SET_CHILD_SUBREAPER above) to which the caller is
               subsequently reparented.  If the parent thread and all
               ancestor subreapers have already terminated by the time
               of the PR_SET_PDEATHSIG operation, then no parent-death
               signal is sent to the caller.

               The parent-death signal is process-directed (see
               signal(7)) and, if the child installs a handler using
               the sigaction(2) SA_SIGINFO flag, the si_pid field of
               the siginfo_t argument of the handler contains the PID
               of the terminating parent process.

               The parent-death signal setting is cleared for the
               child of a fork(2).  It is also (since Linux 2.4.36 /
               2.6.23) cleared when executing a set-user-ID or set-
               group-ID binary, or a binary that has associated capa-
               bilities (see capabilities(7)); otherwise, this value
               is preserved across execve(2).  The parent-death signal
               setting is also cleared upon changes to any of the fol-
               lowing thread credentials: effective user ID, effective
               group ID, filesystem user ID, or filesystem group ID.

          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_PTRACER (since Linux 3.4)
               This is meaningful only when the Yama LSM is enabled
               and in mode 1 ("restricted ptrace", visible via
               /proc/sys/kernel/yama/ptrace_scope). When a "ptracer
               process ID" is passed in arg2, the caller is declaring
               that the ptracer process can ptrace(2) the calling pro-
               cess as if it were a direct process ancestor.  Each
               PR_SET_PTRACER operation replaces the previous "ptracer
               process ID".  Employing PR_SET_PTRACER with arg2 set to
               0 clears the caller's "ptracer process ID".  If arg2 is
               PR_SET_PTRACER_ANY, the ptrace restrictions introduced
               by Yama are effectively disabled for the calling pro-
               cess.

               For further information, see the kernel source file
               Documentation/admin-guide/LSM/Yama.rst (or
               Documentation/security/Yama.txt before Linux 4.13).

          PR_SET_SECCOMP (since Linux 2.6.23)
               Set the secure computing (seccomp) mode for the calling

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               thread, to limit the available system calls.  The more
               recent seccomp(2) system call provides a superset of
               the functionality of PR_SET_SECCOMP.

               The seccomp mode is selected via arg2. (The seccomp
               constants are defined in <linux/seccomp.h>.)

               With arg2 set to SECCOMP_MODE_STRICT, the only system
               calls that the thread is permitted to make are read(2),
               write(2), _exit(2) (but not exit_group(2)), and
               sigreturn(2).  Other system calls result in the deliv-
               ery of a SIGKILL signal.  Strict 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
               available only if the kernel is configured with
               CONFIG_SECCOMP enabled.

               With arg2 set to SECCOMP_MODE_FILTER (since Linux 3.5),
               the system calls allowed are defined by a pointer to a
               Berkeley Packet Filter passed in arg3. This argument is
               a pointer to struct sock_fprog; it can be designed to
               filter arbitrary system calls and system call argu-
               ments.  This mode is available only if the kernel is
               configured with CONFIG_SECCOMP_FILTER enabled.

               If SECCOMP_MODE_FILTER filters permit fork(2), then the
               seccomp mode is inherited by children created by
               fork(2); if execve(2) is permitted, then the seccomp
               mode is preserved across execve(2).  If the filters
               permit prctl() calls, then additional filters can be
               added; they are run in order until the first non-allow
               result is seen.

               For further information, see the kernel source file
               Documentation/userspace-api/seccomp_filter.rst (or
               Documentation/prctl/seccomp_filter.txt before Linux
               4.13).

          PR_GET_SECCOMP (since Linux 2.6.23)
               Return (as the function result) the secure computing
               mode of the calling thread.  If the caller is not in
               secure computing mode, this operation returns 0; if the
               caller is in strict secure computing mode, then the
               prctl() call will cause a SIGKILL signal to be sent to
               the process.  If the caller is in filter mode, and this
               system call is allowed by the seccomp filters, it
               returns 2; otherwise, the process is killed with a
               SIGKILL signal.  This operation is available only if
               the kernel is configured with CONFIG_SECCOMP enabled.

               Since Linux 3.8, the Seccomp field of the

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               /proc/[pid]/status file provides a method of obtaining
               the same information, without the risk that the process
               is killed; see proc(5).

          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_GET_SPECULATION_CTRL (since Linux 4.17)
               Return (as the function result) the state of the specu-
               lation misfeature specified in arg2. Currently, the
               only permitted value for this argument is
               PR_SPEC_STORE_BYPASS (otherwise the call fails with the
               error ENODEV).

               The return value uses bits 0-3 with the following mean-
               ing:

               PR_SPEC_PRCTL
                    Mitigation can be controlled per thread by
                    PR_SET_SPECULATION_CTRL.

               PR_SPEC_ENABLE
                    The speculation feature is enabled, mitigation is
                    disabled.

               PR_SPEC_DISABLE
                    The speculation feature is disabled, mitigation is
                    enabled.

               PR_SPEC_FORCE_DISABLE
                    Same as PR_SPEC_DISABLE but cannot be undone.

               PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
                    Same as PR_SPEC_DISABLE, but the state will be
                    cleared on execve(2).

               If all bits are 0, then the CPU is not affected by the
               speculation misfeature.

               If PR_SPEC_PRCTL is set, then per-thread control of the
               mitigation is available.  If not set, prctl() for the
               speculation misfeature will fail.

               The arg3, arg4, and arg5 arguments must be specified as
               0; otherwise the call fails with the error EINVAL.

          PR_SET_SPECULATION_CTRL (since Linux 4.17)

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               Sets the state of the speculation misfeature specified
               in arg2. The speculation-misfeature settings are per-
               thread attributes.

               Currently, arg2 must be one of:

               PR_SPEC_STORE_BYPASS
                    Set the state of the speculative store bypass mis-
                    feature.

               PR_SPEC_INDIRECT_BRANCH (since Linux 4.20)
                    Set the state of the indirect branch speculation
                    misfeature.

               If arg2 does not have one of the above values, then the
               call fails with the error ENODEV.

               The arg3 argument is used to hand in the control value,
               which is one of the following:

               PR_SPEC_ENABLE
                    The speculation feature is enabled, mitigation is
                    disabled.

               PR_SPEC_DISABLE
                    The speculation feature is disabled, mitigation is
                    enabled.

               PR_SPEC_FORCE_DISABLE
                    Same as PR_SPEC_DISABLE, but cannot be undone.  A
                    subsequent prctl(arg2, PR_SPEC_ENABLE) with the
                    same value for arg2 will fail with the error
                    EPERM.

               PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
                    Same as PR_SPEC_DISABLE, but the state will be
                    cleared on execve(2).  Currently only supported
                    for arg2 equal to PR_SPEC_STORE_BYPASS.

               Any unsupported value in arg3 will result in the call
               failing with the error ERANGE.

               The arg4 and arg5 arguments must be specified as 0;
               otherwise the call fails with the error EINVAL.

               The speculation feature can also be controlled by the
               spec_store_bypass_disable boot parameter.  This parame-
               ter may enforce a read-only policy which will result in
               the prctl() call failing with the error ENXIO.  For
               further details, see the kernel source file
               Documentation/admin-guide/kernel-parameters.txt.  .}f

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          PR_SVE_SET_VL (since Linux 4.15, only on arm64)
               Configure the thread's SVE vector length, as specified
               by (int) arg2. Arguments arg3, arg4, and arg5 are
               ignored.

               The bits of arg2 corresponding to PR_SVE_VL_LEN_MASK
               must be set to the desired vector length in bytes.
               This is interpreted as an upper bound: the kernel will
               select the greatest available vector length that does
               not exceed the value specified.  In particular, speci-
               fying SVE_VL_MAX (defined in <asm/sigcontext.h>) for
               the PR_SVE_VL_LEN_MASK bits requests the maximum sup-
               ported vector length.

               In addition, the other bits of arg2 must be set to one
               of the following combinations of flags:

               0    Perform the change immediately.  At the next
                    execve(2) in the thread, the vector length will be
                    reset to the value configured in
                    /proc/sys/abi/sve_default_vector_length.

               PR_SVE_VL_INHERIT
                    Perform the change immediately.  Subsequent
                    execve(2) calls will preserve the new vector
                    length.

               PR_SVE_SET_VL_ONEXEC
                    Defer the change, so that it is performed at the
                    next execve(2) in the thread.  Further execve(2)
                    calls will reset the vector length to the value
                    configured in
                    /proc/sys/abi/sve_default_vector_length.

               PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT
                    Defer the change, so that it is performed at the
                    next execve(2) in the thread.  Further execve(2)
                    calls will preserve the new vector length.

               In all cases, any previously pending deferred change is
               canceled.

               The call fails with error EINVAL if SVE is not sup-
               ported on the platform, if arg2 is unrecognized or
               invalid, or the value in the bits of arg2 corresponding
               to PR_SVE_VL_LEN_MASK is outside the range
               SVE_VL_MIN..SVE_VL_MAX or is not a multiple of 16.

               On success, a nonnegative value is returned that
               describes the selected configuration.  If
               PR_SVE_SET_VL_ONEXEC was included in arg2, then the
               configuration described by the return value will take

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               effect at the next execve().  Otherwise, the configura-
               tion is already in effect when the PR_SVE_SET_VL call
               returns.  In either case, the value is encoded in the
               same way as the return value of PR_SVE_GET_VL.  Note
               that there is no explicit flag in the return value cor-
               responding to PR_SVE_SET_VL_ONEXEC.

               The configuration (including any pending deferred
               change) is inherited across fork(2) and clone(2).

               For more information, see the kernel source file
               Documentation/arm64/sve.rst (or
               Documentation/arm64/sve.txt before Linux 5.3).

               Warning: Because the compiler or run-time environment
               may be using SVE, using this call without the
               PR_SVE_SET_VL_ONEXEC flag may crash the calling pro-
               cess.  The conditions for using it safely are complex
               and system-dependent.  Don't use it unless you really
               know what you are doing.

          PR_SVE_GET_VL (since Linux 4.15, only on arm64)
               Get the thread's current SVE vector length configura-
               tion.

               Arguments arg2, arg3, arg4, and are ignored.

               Provided that the kernel and platform support SVE, this
               operation always succeeds, returning a nonnegative
               value that describes the current configuration.  The
               bits corresponding to PR_SVE_VL_LEN_MASK contain the
               currently configured vector length in bytes.  The bit
               corresponding to PR_SVE_VL_INHERIT indicates whether
               the vector length will be inherited across execve(2).

               Note that there is no way to determine whether there is
               a pending vector length change that has not yet taken
               effect.

               For more information, see the kernel source file
               Documentation/arm64/sve.rst (or
               Documentation/arm64/sve.txt before Linux 5.3).

          PR_SET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
               Controls support for passing tagged user-space
               addresses to the kernel (i.e., addresses where bits
               56-63 are not all zero).

               The level of support is selected by arg2, which can be
               one of the following:

               0    Addresses that are passed for the purpose of being

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                    dereferenced by the kernel must be untagged.

               PR_TAGGED_ADDR_ENABLE
                    Addresses that are passed for the purpose of being
                    dereferenced by the kernel may be tagged, with the
                    exceptions summarized below.

               The remaining arguments arg3, arg4, and arg5 must all
               be zero.

               On success, the mode specified in arg2 is set for the
               calling thread and the return value is 0.  If the argu-
               ments are invalid, the mode specified in arg2 is unrec-
               ognized, or if this feature is unsupported by the ker-
               nel or disabled via /proc/sys/abi/tagged_addr_disabled,
               the call fails with the error EINVAL.

               In particular, if prctl(PR_SET_TAGGED_ADDR_CTRL, 0, 0,
               0, 0) fails with EINVAL, then all addresses passed to
               the kernel must be untagged.

               Irrespective of which mode is set, addresses passed to
               certain interfaces must always be untagged:

               +o brk(2), mmap(2), shmat(2), shmdt(2), and the
                 new_address argument of mremap(2).

                 (Prior to Linux 5.6 these accepted tagged addresses,
                 but the behaviour may not be what you expect.  Don't
                 rely on it.)

               +o oqpolymorphiccq interfaces that accept pointers to
                 arbitrary types cast to a void * or other generic
                 type, specifically prctl(), ioctl(2), and in general
                 setsockopt(2) (only certain specific setsockopt(2)
                 options allow tagged addresses).

               This list of exclusions may shrink when moving from one
               kernel version to a later kernel version.  While the
               kernel may make some guarantees for backwards compati-
               bility reasons, for the purposes of new software the
               effect of passing tagged addresses to these interfaces
               is unspecified.

               The mode set by this call is inherited across fork(2)
               and clone(2).  The mode is reset by execve(2) to 0
               (i.e., tagged addresses not permitted in the
               user/kernel ABI).

               For more information, see the kernel source file
               Documentation/arm64/tagged-address-abi.rst.

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               Warning: This call is primarily intended for use by the
               run-time environment.  A successful
               PR_SET_TAGGED_ADDR_CTRL call elsewhere may crash the
               calling process.  The conditions for using it safely
               are complex and system-dependent.  Don't use it unless
               you know what you are doing.

          PR_GET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
               Returns the current tagged address mode for the calling
               thread.

               Arguments arg2, arg3, arg4, and must all be zero.

               If the arguments are invalid or this feature is dis-
               abled or unsupported by the kernel, the call fails with
               EINVAL.  In particular, if
               prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) fails with
               EINVAL, then this feature is definitely either unsup-
               ported, or disabled via
               /proc/sys/abi/tagged_addr_disabled. In this case, all
               addresses passed to the kernel must be untagged.

               Otherwise, the call returns a nonnegative value
               describing the current tagged address mode, encoded in
               the same way as the arg2 argument of
               PR_SET_TAGGED_ADDR_CTRL.

               For more information, see the kernel source file
               Documentation/arm64/tagged-address-abi.rst.

          PR_TASK_PERF_EVENTS_DISABLE (since Linux 2.6.31)
               Disable all performance counters attached to the call-
               ing process, regardless of whether the counters were
               created by this process or another process.  Perfor-
               mance counters created by the calling process for other
               processes are unaffected.  For more information on per-
               formance counters, see the Linux kernel source file
               tools/perf/design.txt.

               Originally called PR_TASK_PERF_COUNTERS_DISABLE;
               renamed (retaining the same numerical value) in Linux
               2.6.32.

          PR_TASK_PERF_EVENTS_ENABLE (since Linux 2.6.31)
               The converse of PR_TASK_PERF_EVENTS_DISABLE; enable
               performance counters attached to the calling process.

               Originally called PR_TASK_PERF_COUNTERS_ENABLE; renamed
               in Linux 2.6.32.

          PR_SET_THP_DISABLE (since Linux 3.15)
               Set the state of the "THP disable" flag for the calling

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               thread.  If arg2 has a nonzero value, the flag is set,
               otherwise it is cleared.  Setting this flag provides a
               method for disabling transparent huge pages for jobs
               where the code cannot be modified, and using a malloc
               hook with madvise(2) is not an option (i.e., statically
               allocated data).  The setting of the "THP disable" flag
               is inherited by a child created via fork(2) and is pre-
               served across execve(2).

          PR_GET_THP_DISABLE (since Linux 3.15)
               Return (as the function result) the current setting of
               the "THP disable" flag for the calling thread: either
               1, if the flag is set, or 0, if it is not.

          PR_GET_TID_ADDRESS (since Linux 3.5)
               Return the clear_child_tid address set by
               set_tid_address(2) and the clone(2)
               CLONE_CHILD_CLEARTID flag, in the location pointed to
               by (int **) arg2. This feature is available only if the
               kernel is built with the CONFIG_CHECKPOINT_RESTORE
               option enabled.  Note that since the prctl() system
               call does not have a compat implementation for the
               AMD64 x32 and MIPS n32 ABIs, and the kernel writes out
               a pointer using the kernel's pointer size, this opera-
               tion expects a user-space buffer of 8 (not 4) bytes on
               these ABIs.

          PR_SET_TIMERSLACK (since Linux 2.6.28)
               Each thread has two associated timer slack values: a
               "default" value, and a "current" value.  This operation
               sets the "current" timer slack value for the calling
               thread.  arg2 is an unsigned long value, then maximum
               "current" value is ULONG_MAX and the minimum "current"
               value is 1.  If the nanosecond value supplied in arg2
               is greater than zero, then the "current" value is set
               to this value.  If arg2 is equal to zero, the "current"
               timer slack is reset to the thread's "default" timer
               slack value.

               The "current" timer slack is used by the kernel to
               group timer expirations for the calling thread that are
               close to one another; as a consequence, timer expira-
               tions for the thread may be up to the specified number
               of nanoseconds late (but will never expire early).
               Grouping timer expirations can help reduce system power
               consumption by minimizing CPU wake-ups.

               The timer expirations affected by timer slack are those
               set by select(2), pselect(2), poll(2), ppoll(2),
               epoll_wait(2), epoll_pwait(2), clock_nanosleep(2),
               nanosleep(2), and futex(2) (and thus the library func-
               tions implemented via futexes, including

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               pthread_cond_timedwait(3), pthread_mutex_timedlock(3),
               pthread_rwlock_timedrdlock(3),
               pthread_rwlock_timedwrlock(3), and sem_timedwait(3)).

               Timer slack is not applied to threads that are sched-
               uled under a real-time scheduling policy (see
               sched_setscheduler(2)).

               When a new thread is created, the two timer slack val-
               ues are made the same as the "current" value of the
               creating thread.  Thereafter, a thread can adjust its
               "current" timer slack value via PR_SET_TIMERSLACK.  The
               "default" value can't be changed.  The timer slack val-
               ues of init (PID 1), the ancestor of all processes, are
               50,000 nanoseconds (50 microseconds).  The timer slack
               value is inherited by a child created via fork(2), and
               is preserved across execve(2).

               Since Linux 4.6, the "current" timer slack value of any
               process can be examined and changed via the file
               /proc/[pid]/timerslack_ns. See proc(5).

          PR_GET_TIMERSLACK (since Linux 2.6.28)
               Return (as the function result) the "current" timer
               slack value of the calling thread.

          PR_SET_TIMING (since Linux 2.6.0)
               Set whether to use (normal, traditional) statistical
               process timing or accurate timestamp-based process tim-
               ing, 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)
               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

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               2.6.15; PowerPC, since Linux 2.6.18; Alpha, since Linux
               2.6.22; sh, since Linux 2.6.34; tile, since Linux 3.12)
               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.  Alpha also supports an addi-
               tional flag with the value of 4 and no corresponding
               named constant, which instructs kernel to not fix up
               unaligned accesses (it is analogous to providing the
               UAC_NOFIX flag in SSI_NVPAIRS operation of the
               setsysinfo() system call on Tru64).

          PR_GET_UNALIGN
               (See PR_SET_UNALIGN for information on versions and
               architectures.)  Return unaligned access control bits,
               in the location pointed to by (unsigned int *) arg2.

     RETURN VALUE
          On success, PR_CAP_AMBIENT+PR_CAP_AMBIENT_IS_SET,
          PR_CAPBSET_READ, PR_GET_DUMPABLE, PR_GET_FP_MODE,
          PR_GET_IO_FLUSHER, PR_GET_KEEPCAPS, PR_MCE_KILL_GET,
          PR_GET_NO_NEW_PRIVS, PR_GET_SECUREBITS,
          PR_GET_SPECULATION_CTRL, PR_SVE_GET_VL, PR_SVE_SET_VL,
          PR_GET_TAGGED_ADDR_CTRL, PR_GET_THP_DISABLE, PR_GET_TIMING,
          PR_GET_TIMERSLACK, 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
          EACCES
               option is PR_SET_SECCOMP and arg2 is
               SECCOMP_MODE_FILTER, but the process does not have the
               CAP_SYS_ADMIN capability or has not set the
               no_new_privs attribute (see the discussion of
               PR_SET_NO_NEW_PRIVS above).

          EACCES
               option is PR_SET_MM, and arg3 is PR_SET_MM_EXE_FILE,
               the file is not executable.

          EBADF
               option is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE, and
               the file descriptor passed in arg4 is not valid.

          EBUSY
               option is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE, and
               this the second attempt to change the /proc/pid/exe
               symbolic link, which is prohibited.

          EFAULT
               arg2 is an invalid address.

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          EFAULT
               option is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER,
               the system was built with CONFIG_SECCOMP_FILTER, and
               arg3 is an invalid address.

          EINVAL
               The value of option is not recognized, or not supported
               on this system.

          EINVAL
               option is PR_MCE_KILL or PR_MCE_KILL_GET or PR_SET_MM,
               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_GET_SECCOMP, and the
               kernel was not configured with CONFIG_SECCOMP.

          EINVAL
               option is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER,
               and the kernel was not configured with
               CONFIG_SECCOMP_FILTER.

          EINVAL
               option is PR_SET_MM, and one of the following is true

               *  arg4 or arg5 is nonzero;

               *  arg3 is greater than TASK_SIZE (the limit on the
                  size of the user address space for this architec-
                  ture);

               *  arg2 is PR_SET_MM_START_CODE, PR_SET_MM_END_CODE,
                  PR_SET_MM_START_DATA, PR_SET_MM_END_DATA, or
                  PR_SET_MM_START_STACK, and the permissions of the
                  corresponding memory area are not as required;

               *  arg2 is PR_SET_MM_START_BRK or PR_SET_MM_BRK, and
                  arg3 is less than or equal to the end of the data
                  segment or specifies a value that would cause the
                  RLIMIT_DATA resource limit to be exceeded.

          EINVAL
               option is PR_SET_PTRACER and arg2 is not 0,
               PR_SET_PTRACER_ANY, or the PID of an existing process.

          EINVAL
               option is PR_SET_PDEATHSIG and arg2 is not a valid sig-
               nal number.

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     PRCTL(2)                  (2020-08-13)                   PRCTL(2)

          EINVAL
               option is PR_SET_DUMPABLE and arg2 is neither
               SUID_DUMP_DISABLE nor SUID_DUMP_USER.

          EINVAL
               option is PR_SET_TIMING and arg2 is not
               PR_TIMING_STATISTICAL.

          EINVAL
               option is PR_SET_NO_NEW_PRIVS and arg2 is not equal to
               1 or arg3, arg4, or arg5 is nonzero.

          EINVAL
               option is PR_GET_NO_NEW_PRIVS and arg2, arg3, arg4, or
               arg5 is nonzero.

          EINVAL
               option is PR_SET_THP_DISABLE and arg3, arg4, or arg5 is
               nonzero.

          EINVAL
               option is PR_GET_THP_DISABLE and arg2, arg3, arg4, or
               arg5 is nonzero.

          EINVAL
               option is PR_CAP_AMBIENT and an unused argument (arg4,
               arg5, or, in the case of PR_CAP_AMBIENT_CLEAR_ALL,
               arg3) is nonzero; or arg2 has an invalid value; or arg2
               is PR_CAP_AMBIENT_LOWER, PR_CAP_AMBIENT_RAISE, or
               PR_CAP_AMBIENT_IS_SET and arg3 does not specify a valid
               capability.

          EINVAL
               option was PR_GET_SPECULATION_CTRL or
               PR_SET_SPECULATION_CTRL and unused arguments to prctl()
               are not 0.  EINVAL option is PR_PAC_RESET_KEYS and the
               arguments are invalid or unsupported.  See the descrip-
               tion of PR_PAC_RESET_KEYS above for details.

          EINVAL
               option is PR_SVE_SET_VL and the arguments are invalid
               or unsupported, or SVE is not available on this plat-
               form.  See the description of PR_SVE_SET_VL above for
               details.

          EINVAL
               option is PR_SVE_GET_VL and SVE is not available on
               this platform.

          EINVAL
               option is PR_SET_TAGGED_ADDR_CTRL and the arguments are
               invalid or unsupported.  See the description of

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     PRCTL(2)                  (2020-08-13)                   PRCTL(2)

               PR_SET_TAGGED_ADDR_CTRL above for details.

          EINVAL
               option is PR_GET_TAGGED_ADDR_CTRL and the arguments are
               invalid or unsupported.  See the description of
               PR_GET_TAGGED_ADDR_CTRL above for details.

          ENODEV
               option was PR_SET_SPECULATION_CTRL the kernel or CPU
               does not support the requested speculation misfeature.

          ENXIO
               option was PR_MPX_ENABLE_MANAGEMENT or
               PR_MPX_DISABLE_MANAGEMENT and the kernel or the CPU
               does not support MPX management.  Check that the kernel
               and processor have MPX support.

          ENXIO
               option was PR_SET_SPECULATION_CTRL implies that the
               control of the selected speculation misfeature is not
               possible.  See PR_GET_SPECULATION_CTRL for the bit
               fields to determine which option is available.

          EOPNOTSUPP
               option is PR_SET_FP_MODE and arg2 has an invalid or
               unsupported value.

          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 correspond-
               ing locked flag was set (see capabilities(7)).

          EPERM
               option is PR_SET_SPECULATION_CTRL wherein the specula-
               tion was disabled with PR_SPEC_FORCE_DISABLE and caller
               tried to enable it again.

          EPERM
               option is PR_SET_KEEPCAPS, and the caller's
               SECBIT_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.

          EPERM
               option is PR_SET_MM, and the caller does not have the
               CAP_SYS_RESOURCE capability.

          EPERM

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     PRCTL(2)                  (2020-08-13)                   PRCTL(2)

               option is PR_CAP_AMBIENT and arg2 is
               PR_CAP_AMBIENT_RAISE, but either the capability speci-
               fied in arg3 is not present in the process's permitted
               and inheritable capability sets, or the
               PR_CAP_AMBIENT_LOWER securebit has been set.

          ERANGE
               option was PR_SET_SPECULATION_CTRL and arg3 is not
               PR_SPEC_ENABLE, PR_SPEC_DISABLE, PR_SPEC_FORCE_DISABLE,
               nor PR_SPEC_DISABLE_NOEXEC.

     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, and so on.

     SEE ALSO
          signal(2), core(5)

     COLOPHON
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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