'\" te
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.TH PREAP 1 "Jun 19, 2006"
.SH NAME
preap \- force a defunct process to be reaped by its parent
.SH SYNOPSIS
.LP
.nf
\fBpreap\fR [\fB-F\fR] \fIpid\fR...
.fi

.SH DESCRIPTION
.sp
.LP
A defunct (or zombie) process is one whose exit status has yet to be reaped by
its parent. The exit status is reaped by way of the \fBwait\fR(3C),
\fBwaitid\fR(2), or \fBwaitpid\fR(3C) system call. In the normal course of
system operation, zombies can occur, but are typically short-lived. This can
happen if a parent exits without having reaped the exit status of some or all
of its children. In that case, those children are reparented to \fBPID 1\fR.
See \fBinit\fR(8), which periodically reaps such processes.
.sp
.LP
An irresponsible parent process can not exit for a very long time and thus
leave zombies on the system. Since the operating system destroys nearly all
components of a process before it becomes defunct, such defunct processes do
not normally impact system operation. However, they do consume a small amount
of system memory.
.sp
.LP
\fBpreap\fR forces the parent of the process specified by \fIpid\fR to
\fBwaitid\fR(2) for \fIpid\fR, if \fIpid\fR represents a defunct process.
.sp
.LP
\fBpreap\fR attempts to prevent the administrator from unwisely reaping a child
process which might soon be reaped by the parent, if:
.RS +4
.TP
.ie t \(bu
.el o
The process is a child of \fBinit\fR(8).
.RE
.RS +4
.TP
.ie t \(bu
.el o
The parent process is stopped and might wait on the child when it is again
allowed to run.
.RE
.RS +4
.TP
.ie t \(bu
.el o
The process has been defunct for less than one minute.
.RE
.SH OPTIONS
.sp
.LP
The following option is supported:
.sp
.ne 2
.na
\fB\fB-F\fR\fR
.ad
.RS 6n
Forces the parent to reap the child, overriding safety checks.
.RE

.SH OPERANDS
.sp
.LP
The following operand is supported:
.sp
.ne 2
.na
\fB\fIpid\fR\fR
.ad
.RS 7n
Process \fBID\fR list.
.RE

.SH USAGE
.sp
.LP
Caution should be exercised when using the \fB-F\fR flag. Imposing two
controlling processes on one victim process can lead to chaos. Safety is
assured only if the primary controlling process, typically a debugger, has
stopped the victim process and the primary controlling process is doing nothing
at the moment of application of the \fBproc\fR tool in question.
.SH EXIT STATUS
.sp
.LP
The following exit values are returned by \fBpreap\fR, which prints the exit
status of each target process reaped:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 12n
Successfully operation.
.RE

.sp
.ne 2
.na
\fBnon-zero\fR
.ad
.RS 12n
Failure, such as no such process, permission denied, or invalid option.
.RE

.SH SEE ALSO
.sp
.LP
.BR proc (1),
.BR waitid (2),
.BR wait (3C),
.BR waitpid (3C),
.BR proc (5),
.BR attributes (7),
.BR init (8)
.SH WARNINGS
.sp
.LP
\fBpreap\fR should be applied sparingly and only in situations in which the
administrator or developer has confirmed that defunct processes are not reaped
by the parent process. Otherwise, applying \fBpreap\fR can damage the parent
process in unpredictable ways.