Ubuntu Manpage: procctl — control processes

Provided by: freebsd-manpages_11.1-3_all

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.

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_enocap 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_enocap above, which gives
independent global control of signal delivery.

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.

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.