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     procctl — control processes


     Standard C Library (libc, -lc)


     #include <sys/procctl.h>

     procctl(idtype_t idtype, id_t id, int cmd, void *data);


     The procctl() system call provides for control over processes.  The idtype and id arguments
     specify the set of processes to control.  If multiple processes match the identifier,
     procctl will make a “best effort” to control as many of the selected processes as possible.
     An error is only returned if no selected processes successfully complete the request.  The
     following identifier types are supported:

     P_PID   Control the process with the process ID id.

     P_PGID  Control processes belonging to the process group with the ID id.

     The control request to perform is specified by the cmd argument.  The following commands are

     PROC_ASLR_CTL        Controls the Address Space Layout Randomization (ASLR) in the program
                          images created by execve(2) in the specified process or its descendants
                          that did not changed the control nor modified it by other means.  The
                          data parameter must point to the integer variable holding one of the
                          following values:

                          PROC_ASLR_FORCE_ENABLE   Request that ASLR is enabled after execution,
                                                   even if it is disabled system-wide.  The image
                                                   flag and set-uid might prevent ASLR enablement

                          PROC_ASLR_FORCE_DISABLE  Request that ASLR is disabled after execution.
                                                   Same notes as for PROC_ASLR_FORCE_ENABLE

                          PROC_ASLR_NOFORCE        Use system-wide configured policy for ASLR.

     PROC_ASLR_STATUS     Returns the current status of ASLR enablement for the target process.
                          The data parameter must point to the integer variable, where one of the
                          following values is written:




                          If the currently executed image in the process itself has ASLR enabled,
                          the PROC_ASLR_ACTIVE flag is or-ed with the value listed above.

     PROC_SPROTECT        Set process protection state.  This is used to mark a process as
                          protected from being killed if the system exhausts the available memory
                          and swap.  The data parameter must point to an integer containing an
                          operation and zero or more optional flags.  The following operations
                          are supported:

                          PPROT_SET    Mark the selected processes as protected.

                          PPROT_CLEAR  Clear the protected state of selected processes.

                          The following optional flags are supported:

                          PPROT_DESCEND  Apply the requested operation to all child processes of
                                         each selected process in addition to each selected

                          PPROT_INHERIT  When used with PPROT_SET, mark all future child
                                         processes of each selected process as protected.  Future
                                         child processes will also mark all of their future child

     PROC_REAP_ACQUIRE    Acquires the reaper status for the current process.  Reaper status
                          means that children orphaned by the reaper's descendants that were
                          forked after the acquisition of reaper status are reparented to the
                          reaper process.  After system initialization, init(8) is the default

     PROC_REAP_RELEASE    Release the reaper state for the current process.  The reaper of the
                          current process becomes the new reaper of the current process's

     PROC_REAP_STATUS     Provides information about the reaper of the specified process, or the
                          process itself when it is a reaper.  The data argument must point to a
                          procctl_reaper_status structure which is filled in by the syscall on
                          successful return.

                          struct procctl_reaper_status {
                                  u_int   rs_flags;
                                  u_int   rs_children;
                                  u_int   rs_descendants;
                                  pid_t   rs_reaper;
                                  pid_t   rs_pid;
                          The rs_flags may have the following flags returned:

                          REAPER_STATUS_OWNED     The specified process has acquired reaper
                                                  status and has not released it.  When the flag
                                                  is returned, the specified process id, pid,
                                                  identifies the reaper, otherwise the rs_reaper
                                                  field of the structure is set to the pid of the
                                                  reaper for the specified process id.

                          REAPER_STATUS_REALINIT  The specified process is the root of the reaper
                                                  tree, i.e., init(8).

                          The rs_children field returns the number of children of the reaper
                          among the descendants.  It is possible to have a child whose reaper is
                          not the specified process, since the reaper for any existing children
                          is not reset on the PROC_REAP_ACQUIRE operation.  The rs_descendants
                          field returns the total number of descendants of the reaper(s), not
                          counting descendants of the reaper in the subtree.  The rs_reaper field
                          returns the reaper pid.  The rs_pid returns the pid of one reaper child
                          if there are any descendants.

     PROC_REAP_GETPIDS    Queries the list of descendants of the reaper of the specified process.
                          The request takes a pointer to a procctl_reaper_pids structure in the
                          data parameter.

                          struct procctl_reaper_pids {
                                  u_int   rp_count;
                                  struct procctl_reaper_pidinfo *rp_pids;
                          When called, the rp_pids field must point to an array of
                          procctl_reaper_pidinfo structures, to be filled in on return, and the
                          rp_count field must specify the size of the array, into which no more
                          than rp_count elements will be filled in by the kernel.

                          The struct procctl_reaper_pidinfo structure provides some information
                          about one of the reaper's descendants.  Note that for a descendant that
                          is not a child, it may be incorrectly identified because of a race in
                          which the original child process exited and the exited process's pid
                          was reused for an unrelated process.

                          struct procctl_reaper_pidinfo {
                                  pid_t   pi_pid;
                                  pid_t   pi_subtree;
                                  u_int   pi_flags;
                          The pi_pid field is the process id of the descendant.  The pi_subtree
                          field provides the pid of the child of the reaper, which is the
                          (grand-)parent of the process.  The pi_flags field returns the
                          following flags, further describing the descendant:

                          REAPER_PIDINFO_VALID   Set to indicate that the procctl_reaper_pidinfo
                                                 structure was filled in by the kernel.  Zero-
                                                 filling the rp_pids array and testing the
                                                 REAPER_PIDINFO_VALID flag allows the caller to
                                                 detect the end of the returned array.

                          REAPER_PIDINFO_CHILD   The pi_pid field identifies the direct child of
                                                 the reaper.

                          REAPER_PIDINFO_REAPER  The reported process is itself a reaper.  The
                                                 descendants of the subordinate reaper are not

     PROC_REAP_KILL       Request to deliver a signal to some subset of the descendants of the
                          reaper.  The data parameter must point to a procctl_reaper_kill
                          structure, which is used both for parameters and status return.

                          struct procctl_reaper_kill {
                                  int     rk_sig;
                                  u_int   rk_flags;
                                  pid_t   rk_subtree;
                                  u_int   rk_killed;
                                  pid_t   rk_fpid;
                          The rk_sig field specifies the signal to be delivered.  Zero is not a
                          valid signal number, unlike for kill(2).  The rk_flags field further
                          directs the operation.  It is or-ed from the following flags:

                          REAPER_KILL_CHILDREN  Deliver the specified signal only to direct
                                                children of the reaper.

                          REAPER_KILL_SUBTREE   Deliver the specified signal only to descendants
                                                that were forked by the direct child with pid
                                                specified in the rk_subtree field.
                          If neither the REAPER_KILL_CHILDREN nor the REAPER_KILL_SUBTREE flags
                          are specified, all current descendants of the reaper are signalled.

                          If a signal was delivered to any process, the return value from the
                          request is zero.  In this case, the rk_killed field identifies the
                          number of processes signalled.  The rk_fpid field is set to the pid of
                          the first process for which signal delivery failed, e.g., due to
                          permission problems.  If no such process exists, the rk_fpid field is
                          set to -1.

     PROC_TRACE_CTL       Enable or disable tracing of the specified process(es), according to
                          the value of the integer argument.  Tracing includes attachment to the
                          process using the ptrace(2) and ktrace(2), debugging sysctls, hwpmc(4),
                          dtrace(1), and core dumping.  Possible values for the data argument

                          PROC_TRACE_CTL_ENABLE        Enable tracing, after it was disabled by
                                                       PROC_TRACE_CTL_DISABLE.  Only allowed for

                          PROC_TRACE_CTL_DISABLE       Disable tracing for the specified process.
                                                       Tracing is re-enabled when the process
                                                       changes the executing program with the
                                                       execve(2) syscall.  A child inherits the
                                                       trace settings from the parent on fork(2).

                          PROC_TRACE_CTL_DISABLE_EXEC  Same as PROC_TRACE_CTL_DISABLE, but the
                                                       setting persists for the process even
                                                       after execve(2).

     PROC_TRACE_STATUS    Returns the current tracing status for the specified process in the
                          integer variable pointed to by data.  If tracing is disabled, data is
                          set to -1.  If tracing is enabled, but no debugger is attached by the
                          ptrace(2) syscall, data is set to 0.  If a debugger is attached, data
                          is set to the pid of the debugger process.

     PROC_TRAPCAP_CTL     Controls the capability mode sandbox actions for the specified
                          sandboxed processes, on a return from any syscall which gives either a
                          ENOTCAPABLE or ECAPMODE error.  If the control is enabled, such errors
                          from the syscalls cause delivery of the synchronous SIGTRAP signal to
                          the thread immediately before returning from the syscalls.

                          Possible values for the data argument are:

                          PROC_TRAPCAP_CTL_ENABLE   Enable the SIGTRAP signal delivery on
                                                    capability mode access violations.  The
                                                    enabled mode is inherited by the children of
                                                    the process, and is kept after fexecve(2)

                          PROC_TRAPCAP_CTL_DISABLE  Disable the signal delivery on capability
                                                    mode access violations.  Note that the global
                                                    sysctl kern.trap_enotcap might still cause
                                                    the signal to be delivered.  See capsicum(4).

                          On signal delivery, the si_errno member of the siginfo signal handler
                          parameter is set to the syscall error value, and the si_code member is
                          set to TRAP_CAP.

                          See capsicum(4) for more information about the capability mode.

     PROC_TRAPCAP_STATUS  Return the current status of signalling capability mode access
                          violations for the specified process.  The integer value pointed to by
                          the data argument is set to the PROC_TRAPCAP_CTL_ENABLE value if the
                          process control enables signal delivery, and to
                          PROC_TRAPCAP_CTL_DISABLE otherwise.

                          See the note about sysctl kern.trap_enotcap above, which gives
                          independent global control of signal delivery.

     PROC_PDEATHSIG_CTL   Request the delivery of a signal when the parent of the calling process
                          exits.  idtype must be P_PID and id must be the either caller's pid or
                          zero, with no difference in effect.  The value is cleared for child
                          processes and when executing set-user-ID or set-group-ID binaries.  arg
                          must point to a value of type int indicating the signal that should be
                          delivered to the caller.  Use zero to cancel a previously requested
                          signal delivery.

                          Query the current signal number that will be delivered when the parent
                          of the calling process exits.  idtype must be P_PID and id must be the
                          either caller's pid or zero, with no difference in effect.  arg must
                          point to a memory location that can hold a value of type int.  If
                          signal delivery has not been requested, it will contain zero on return.

     PROC_STACKGAP_CTL    Controls the stack gaps in the specified process.  A stack gap is the
                          part of the growth area for a MAP_STACK mapped region that is reserved
                          and never filled by memory.  Instead, the process is guaranteed to
                          receive a SIGSEGV signal on accessing pages in the gap.  Gaps protect
                          against stack overflow corrupting memory adjacent to the stack.

                          The data argument must point to an integer variable containing flags.
                          The following flags are allowed:

                          PROC_STACKGAP_ENABLE        This flag is only accepted for consistency
                                                      with PROC_STACKGAP_STATUS.  If stack gaps
                                                      are enabled, the flag is ignored.  If
                                                      disabled, the flag causes an EINVAL error
                                                      to be returned.  After gaps are disabled in
                                                      a process, they can only be re-enabled when
                                                      an execve(2) is performed.

                          PROC_STACKGAP_DISABLE       Disable stack gaps for the process.  For
                                                      existing stacks, the gap is no longer a
                                                      reserved part of the growth area and can be
                                                      filled by memory on access.

                          PROC_STACKGAP_ENABLE_EXEC   Enable stack gaps for programs started
                                                      after an execve(2) by the specified

                          PROC_STACKGAP_DISABLE_EXEC  Inherit disabled stack gaps state after
                                                      execve(2).  In other words, if the
                                                      currently executing program has stack gaps
                                                      disabled, they are kept disabled on exec.
                                                      If gaps were enabled, they are kept enabled
                                                      after exec.

                          The stack gap state is inherited from the parent on fork(2).

                          Returns the current stack gap state for the specified process.  data
                          must point to an integer variable, which is used to return a bitmask
                          consisting of the following flags:

                          PROC_STACKGAP_ENABLE        Stack gaps are enabled.

                          PROC_STACKGAP_DISABLE       Stack gaps are disabled.

                          PROC_STACKGAP_ENABLE_EXEC   Stack gaps are enabled in the process after

                          PROC_STACKGAP_DISABLE_EXEC  Stack gaps are disabled in the process
                                                      after execve(2).


     PROC_KPTI_CTL     AMD64 only.  Controls the Kernel Page Table Isolation (KPTI) option for
                       the children of the specified process.  For the command to work, the
                       vm.pmap.kpti tunable must be enabled on boot.  It is not possible to
                       change the KPTI setting for a running process, except at the execve(2),
                       where the address space is reinitialized.

                       The data parameter must point to an integer variable containing one of the
                       following commands:

                       PROC_KPTI_CTL_ENABLE_ON_EXEC   Enable KPTI after execve(2).

                       PROC_KPTI_CTL_DISABLE_ON_EXEC  Disable KPTI after execve(2).  Only root or
                                                      a process having the PRIV_IO privilege
                                                      might use this option.

     PROC_KPTI_STATUS  Returns the current KPTI status for the specified process.  data must
                       point to the integer variable, which returns the following statuses:



                       The status is or-ed with the PROC_KPTI_STATUS_ACTIVE in case KPTI is
                       active for the current address space of the process.


     Disabling tracing on a process should not be considered a security feature, as it is
     bypassable both by the kernel and privileged processes, and via other system mechanisms.  As
     such, it should not be utilized to reliably protect cryptographic keying material or other
     confidential data.


     If an error occurs, a value of -1 is returned and errno is set to indicate the error.


     The procctl() system call will fail if:

     [EFAULT]           The arg parameter points outside the process's allocated address space.

     [EINVAL]           The cmd argument specifies an unsupported command.

                        The idtype argument specifies an unsupported identifier type.

     [EPERM]            The calling process does not have permission to perform the requested
                        operation on any of the selected processes.

     [ESRCH]            No processes matched the requested idtype and id.

     [EINVAL]           An invalid operation or flag was passed in arg for a PROC_SPROTECT

     [EPERM]            The idtype argument is not equal to P_PID, or id is not equal to the pid
                        of the calling process, for PROC_REAP_ACQUIRE or PROC_REAP_RELEASE

     [EINVAL]           Invalid or undefined flags were passed to a PROC_REAP_KILL request.

     [EINVAL]           An invalid or zero signal number was requested for a PROC_REAP_KILL

     [EINVAL]           The PROC_REAP_RELEASE request was issued by the init(8) process.

     [EBUSY]            The PROC_REAP_ACQUIRE request was issued by a process that had already
                        acquired reaper status and has not yet released it.

     [EBUSY]            The PROC_TRACE_CTL request was issued for a process already being traced.

     [EPERM]            The PROC_TRACE_CTL request to re-enable tracing of the process
                        (PROC_TRACE_CTL_ENABLE), or to disable persistence of
                        PROC_TRACE_CTL_DISABLE on execve(2) was issued for a non-current process.

     [EINVAL]           The value of the integer data parameter for the PROC_TRACE_CTL or
                        PROC_TRAPCAP_CTL request is invalid.

     [EINVAL]           The PROC_PDEATHSIG_CTL or PROC_PDEATHSIG_STATUS request referenced an
                        unsupported id, idtype or invalid signal number.


     dtrace(1), cap_enter(2), kill(2), ktrace(2), ptrace(2), wait(2), capsicum(4), hwpmc(4),


     The procctl() function appeared in FreeBSD 10.0.

     The reaper facility is based on a similar feature of Linux and DragonflyBSD, and first
     appeared in FreeBSD 10.2.

     The PROC_PDEATHSIG_CTL facility is based on the prctl(PR_SET_PDEATHSIG, ...) feature of
     Linux, and first appeared in FreeBSD 11.2.

     The ASLR support was added to system for the checklists compliance in FreeBSD 13.0.