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.Dd December 2, 2014
.Dt PROCCTL 2
.Os
.Sh NAME
.Nm procctl
.Nd control reaping of sub-processes and other functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/procctl.h
.Ft int
.Fo procctl
.Fa "idtype_t idtype"
.Fa "id_t id"
.Fa "int cmd"
.Fa "void *data"
.Fc
.Sh DESCRIPTION
The
.Fn procctl
system call applies certain process-related control operations to the system.
The
.Fa idtype
argument may be
.Dv P_PID
or
.Dv P_PGID ,
and the
.Fa id
argument is either a process id or a process group id, or 0 indicating
the current process or process group.
.Pp
Note that currently all functions only operate on the current process.
.Sh REAPER OPERATION
The
.Fn procctl
system call may be used by a process to take-over the reaping task from init
for any forked sub-process, recursively (for all children thereafter) which
would otherwise reparent to init.
This allows a chain of control to be maintained no matter what the
sub-process does.
.Pp
Any process may become a reaper for its sub-processes.
The feature may also be used recursively, or independently, to
create reaping domains or sub-domains.
.Pp
This call is typically used by service monitoring programs, jails, or
chroots to ensure that the underlying services cannot get away from under
the monitor.
.Sh CONTROL OPERATIONS
The following operations are defined in
.In sys/procctl.h :
.Bl -tag -width indent
.It Dv PROC_REAP_ACQUIRE
Become a reaper for all sub-processes forked after the call returns.
The data argument is ignored and can be NULL.
.It Dv PROC_REAP_RELEASE
Release reaping duties, reaping returns to normal operation.
The data argument is ignored and can be NULL.
.It Dv PROC_REAP_STATUS
Request status.
The supplied data structure is loaded with the current reaper status.
The data argument may be NULL, which can be used to test whether
the system call exists or not (assuming you catch
.Er ENOSYS ) .
See the include file for more information.
.Pp
Current status flags, indicating whether reaping is acquired.
If reaping is acquired additional data will be returned.
.Pp
When reaping is acquired, the first running pid under the reaper
is also loaded into the data structure, or -1 if there are none
running.
Callers wishing to destroy all processes under management can
kill the process in question, waitpid it, and loop until no processes
remain.
This is guaranteed to ultimately irradicate everything that was directly
or indirectly started under the reaper.
.It Dv PROC_PDEATHSIG_CTL
The argument is a pointer to an integer specifying the signal that should
be delivered to the current process when its parent process exits.
A value of 0 cancels any previously set signal.
.Pp
Any previously set signal is automatically canceled in the child process of
a
.Fn fork
or when a suid or sgid program is exec'd.
.Pp
Only the current process pid or 0 may be specified.  Both have the same effect.
.It Dv PROC_PDEATHSIG_STATUS
The argument is a pointer to an integer variable which will be filled in
with the current pdeathsig signal, or 0 if the feature is not enabled.
.Pp
Only the current process pid or 0 may be specified.  Both have the same effect.
.El
.Sh RETURN VALUES
.Rv -std
.Pp
If a data structure is supplied, data may be read or written to it
according to the op code.
Only sufficient data to support the requested operation is read or
written.
.Sh ERRORS
The
.Fn procctl
function will fail when one of the following occurs:
.Bl -tag -width Er
.It Bq Er EALREADY
An attempt to acquire reaping is made but the current
process has already acquired the feature.
.It Bq Er ENOTCONN
An attempt to release reaping is made but the current
process has not currently acquired the feature.
.It Bq Er EINVAL
The operation is not supported.
.El
.\".Sh SEE ALSO
.Sh HISTORY
The
.Fn procctl
system call first appeared in
.Dx 4.0 .
.Sh AUTHORS
.An -nosplit
The
.Fn procctl
system call was written by
.An Matthew Dillon .