--- name: "procctl" section: "2freebsd" platform: "linux" package: "freebsd-manpages" version: "12.2-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/procctl/2freebsd" --- # procctl(2freebsd) control processes ## NAME **procctl** – control processes ## LIBRARY Standard C Library (libc, -lc) ## SYNOPSIS **#include \** *int*\ **procctl**(*idtype\_t idtype*, *id\_t id*, *int cmd*, *void \*data*); ## DESCRIPTION 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 supported: - PROC\_ASLR\_CTL Controls the Address Space Layout Randomization (ASLR) in the program images created by [execve(2)](/execve/2.md) 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 still. - PROC\_ASLR\_FORCE\_DISABLE Request that ASLR is disabled after execution. Same notes as for PROC\_ASLR\_FORCE\_ENABLE apply. - 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: - PROC\_ASLR\_FORCE\_ENABLE - PROC\_ASLR\_FORCE\_DISABLE - PROC\_ASLR\_NOFORCE 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 process. - 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 processes. - 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)](/init/8.md) is the default reaper. - 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 descendants. - 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)](/init/8.md). 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 reported. - 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)](/kill/2.md). 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)](/ptrace/2.md) and [ktrace(2)](/ktrace/2.md), debugging sysctls, [hwpmc(4)](/hwpmc/4.md), [dtrace(1)](/dtrace/1.md), and core dumping. Possible values for the *data* argument are: - PROC\_TRACE\_CTL\_ENABLE Enable tracing, after it was disabled by PROC\_TRACE\_CTL\_DISABLE. Only allowed for self. - 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)](/execve/2.md) syscall. A child inherits the trace settings from the parent on [fork(2)](/fork/2.md). - PROC\_TRACE\_CTL\_DISABLE\_EXEC Same as PROC\_TRACE\_CTL\_DISABLE, but the setting persists for the process even after [execve(2)](/execve/2.md). - 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)](/ptrace/2.md) 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)](/fexecve/2.md) calls. - 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)](/capsicum/4.md). 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)](/capsicum/4.md) 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. - PROC\_PDEATHSIG\_STATUS 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)](/execve/2.md) 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)](/execve/2.md) by the specified process. - PROC\_STACKGAP\_DISABLE\_EXEC Inherit disabled stack gaps state after [execve(2)](/execve/2.md). 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)](/fork/2.md). - PROC\_STACKGAP\_STATUS 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 [execve(2)](/execve/2.md). - PROC\_STACKGAP\_DISABLE\_EXEC Stack gaps are disabled in the process after [execve(2)](/execve/2.md). ## x86 MACHINE-SPECIFIC REQUESTS - 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)](/execve/2.md), 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)](/execve/2.md). - PROC\_KPTI\_CTL\_DISABLE\_ON\_EXEC Disable KPTI after [execve(2)](/execve/2.md). 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: - PROC\_KPTI\_CTL\_ENABLE\_ON\_EXEC - PROC\_KPTI\_CTL\_DISABLE\_ON\_EXEC The status is or-ed with the *PROC\_KPTI\_STATUS\_ACTIVE* in case KPTI is active for the current address space of the process. ## NOTES 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. ## RETURN VALUES If an error occurs, a value of -1 is returned and *errno* is set to indicate the error. ## ERRORS 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 command. - \[EPERM\] 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 requests. - \[EINVAL\] 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 request. - \[EINVAL\] The PROC\_REAP\_RELEASE request was issued by the [init(8)](/init/8.md) 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)](/execve/2.md) 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. ## SEE ALSO [dtrace(1)](/dtrace/1.md), [cap\_enter(2)](/cap_enter/2.md), [kill(2)](/kill/2.md), [ktrace(2)](/ktrace/2.md), [ptrace(2)](/ptrace/2.md), [wait(2)](/wait/2.md), [capsicum(4)](/capsicum/4.md), [hwpmc(4)](/hwpmc/4.md), [init(8)](/init/8.md) ## HISTORY 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.