cfb5f76865
A "process descriptor" file descriptor is used to manage processes without using the PID namespace. This is required for Capsicum's Capability Mode, where the PID namespace is unavailable. New system calls pdfork(2) and pdkill(2) offer the functional equivalents of fork(2) and kill(2). pdgetpid(2) allows querying the PID of the remote process for debugging purposes. The currently-unimplemented pdwait(2) will, in the future, allow querying rusage/exit status. In the interim, poll(2) may be used to check (and wait for) process termination. When a process is referenced by a process descriptor, it does not issue SIGCHLD to the parent, making it suitable for use in libraries---a common scenario when using library compartmentalisation from within large applications (such as web browsers). Some observers may note a similarity to Mach task ports; process descriptors provide a subset of this behaviour, but in a UNIX style. This feature is enabled by "options PROCDESC", but as with several other Capsicum kernel features, is not enabled by default in GENERIC 9.0. Reviewed by: jhb, kib Approved by: re (kib), mentor (rwatson) Sponsored by: Google Inc
183 lines
4.8 KiB
Groff
183 lines
4.8 KiB
Groff
.\"
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.\" Copyright (c) 2009-2010 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" This software was developed at the University of Cambridge Computer
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.\" Laboratory with support from a grant from Google, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 16, 2011
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.Dt PDFORK 2
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.Os
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.Sh NAME
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.Nm pdfork ,
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.Nm pdgetpid ,
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.Nm pdkill ,
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.Nm pdwait4
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.Nd System calls to manage process descriptors
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/procdesc.h
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.Ft int
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.Fn pdfork "int *fdp" "int flags"
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.Ft int
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.Fn pdgetpid "int fd" "pid_t *pidp"
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.Ft int
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.Fn pdkill "int fd" "int signum"
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.Ft int
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.Fn pdwait4 "int fd" "int *status" "int options" "struct rusage *rusage"
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.Sh DESCRIPTION
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Process descriptors are special file descriptors that represent processes,
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and are created using
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.Fn pdfork ,
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a variant of
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.Xr fork 2 ,
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which, if successful, returns a process descriptor in the integer pointed to
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by
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.Fa pidp .
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Processes created via
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.Fn pdfork
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will not cause
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.Dv SIGCHLD
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on termination.
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.Fn pdfork
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can accept the flags:
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.Bl -tag -width ".Dv PD_DAEMON"
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.It Dv PD_DAEMON
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Instead of the default terminate-on-close behaviour, allow the process to
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live until it is explicitly killed with
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.Xr kill 2 .
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.Pp
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This option is not permitted in Capsicum capability mode (see
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.Xr cap_enter 2 ) .
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.El
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.Pp
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.Fn pdgetpid
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queries the process ID (PID) if the process descriptor
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.Fa fd .
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.Pp
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.Fn pdkill
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is functionally identical to
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.Xr kill 2 ,
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except that it accepts a process descriptor,
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.Fa fd ,
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rather than a PID.
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.Pp
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.Fn pdwait4
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behaves identially to
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.Xr wait4 2 ,
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but operates with respect to a process descriptor argument rather than a PID.
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.Pp
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The following system calls also have effects specific to process descriptors:
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.Pp
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.Xr fstat 2
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queries status of a process descriptor; currently only the
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.Fa st_mode ,
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.Fa st_birthtime ,
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.Fa st_atime ,
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.Fa st_ctime
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and
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.Fa st_mtime
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fields are defined. If the owner read, write, and execute bits are set then the
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process represented by the process descriptor is still alive.
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.Pp
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.Xr poll 2
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and
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.Xr select 2
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allow waiting for process state transitions; currently only
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.Dv POLLHUP
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is defined, and will be raised when the process dies.
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.Pp
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.Xr close 2
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will close the process descriptor unless
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.Dv PD_DAEMON
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is set; if the process is still alive and this is
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the last reference to the process descriptor, the process will be terminated
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with the signal
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.Dv SIGKILL .
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.Sh RETURN VALUES
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.Fn pdfork
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returns a PID, 0 or -1, as
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.Xr fork 2
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does.
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.Pp
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.Fn pdgetpid
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and
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.Fn pdkill
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return 0 on success and -1 on failure.
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.Pp
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.Fn pdwait4
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returns a PID on success and -1 on failure.
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.Sh ERRORS
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These functions may return the same error numbers as their PID-based equivalents
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(e.g.
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.Fn pdfork
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may return the same error numbers as
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.Xr fork 2 ) ,
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with the following additions:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The signal number given to
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.Fn pdkill
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is invalid.
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.It Bq Er ENOTCAPABLE
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The process descriptor being operated on has insufficient rights (e.g.
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.Dv CAP_PDKILL
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for
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.Fn pdkill ) .
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.El
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.Sh SEE ALSO
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.Xr close 2 ,
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.Xr fork 2 ,
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.Xr fstat 2 ,
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.Xr kill 2 ,
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.Xr poll 2 ,
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.Xr wait4 2
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.Sh HISTORY
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The
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.Fn pdfork ,
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.Fn pdgetpid ,
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.Fn pdkill
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and
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.Fn pdwait4
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system calls first appeared in
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.Fx 9.0 .
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.Pp
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Support for process descriptors mode was developed as part of the
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.Tn TrustedBSD
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Project.
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.Sh AUTHORS
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.An -nosplit
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These functions and the capability facility were created by
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.An "Robert N. M. Watson" Aq rwatson@FreeBSD.org
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and
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.An "Jonathan Anderson" Aq jonathan@FreeBSD.org
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at the University of Cambridge Computer Laboratory with support from a grant
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from Google, Inc.
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.Sh BUGS
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.Fn pdwait4
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has not yet been implemented.
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