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NAME
procctl — control processes
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/procctl.h>
int
procctl(idtype_t idtype, id_t id, int cmd, void *arg);
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_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 arg
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) 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).
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). 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 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) 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) 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).
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.
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.
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) 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.
SEE ALSO
dtrace(1), cap_enter(2,) kill(2), ktrace(2), ptrace(2), wait(2), capsicum(4), hwpmc(4), init(8)
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.