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Kyle Evans
4fd518fcb2
We sometimes store sensitive things in the kenv that get zapped, but we really shouldn't rely on that zapping to actually happen. Most unprivileged processes don't really need to read from the kernel environment in the first place, so add a knob that allows it to be disabled. Note that we consider jailed root to be unprivileged from this perspective; they have their own meta/env concepts and we should encourage users to take advantage of those for passing information to jails. "Hey we should do something about that": dch Reviewed by: imp, ziaee, zlei (all slightly previous version) Differential Revision: https://reviews.freebsd.org/D57697
197 lines
4.9 KiB
Plaintext
197 lines
4.9 KiB
Plaintext
.\"
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.\" Copyright (C) 2002 Chad David <[email protected]>. All rights reserved.
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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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), 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 COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" 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 SUCH
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.\" DAMAGE.
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.\"
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.Dd June 22, 2026
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.Dt KENV 2
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.Os
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.Sh NAME
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.Nm kenv
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.Nd kernel environment
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In kenv.h
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.Ft int
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.Fn kenv "int action" "const char *name" "char *value" "int len"
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.Sh DESCRIPTION
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The
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.Fn kenv
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system call manipulates kernel environment variables.
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It supports the well known userland actions of getting, setting and unsetting
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environment variables, as well as the ability to dump all of the entries in
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the kernel environment.
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.Pp
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The
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.Fa action
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argument can be one of the following:
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.Bl -tag -width ".Dv KENV_DUMP_LOADER"
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.It Dv KENV_GET
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Get the
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.Fa value
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of the variable with the given
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.Fa name .
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The size of the
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.Fa value
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buffer is given by
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.Fa len ,
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which should be at least
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.Dv KENV_MVALLEN
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+ 1 bytes to avoid truncation and to ensure NUL termination.
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.It Dv KENV_SET
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Set or add a variable.
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The
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.Fa name
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and
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.Fa value
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are limited to
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.Dv KENV_MNAMELEN
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and
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.Dv KENV_MVALLEN
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characters, respectively
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.Pq not including the NUL terminator.
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The
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.Fa len
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argument indicates the length of the
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.Fa value
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and must include the NUL terminator.
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This option is only available to the superuser.
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.It Dv KENV_UNSET
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Unset the variable with the given
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.Fa name .
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The
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.Fa value
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and
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.Fa len
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arguments are ignored.
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This option is only available to the superuser.
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.It Dv KENV_DUMP
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Dump as much of the dynamic kernel environment as will fit in
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.Fa value ,
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whose size is given in
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.Fa len .
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If
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.Fa value
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is
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.Dv NULL ,
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.Fn kenv
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will return the number of bytes required to copy out the entire environment.
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The
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.Fa name
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is ignored.
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.It Dv KENV_DUMP_LOADER
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Dump the static environment provided by
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.Xr loader 8 ,
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with semantics identical to
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.Dv KENV_DUMP .
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Duplicate and malformed variables originally present in this environment are
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discarded by the kernel and will not appear in the output.
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.It Dv KENV_DUMP_STATIC
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Dump the static environment defined by the kernel
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.Xr config 5 .
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The semantics are identical to
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.Dv KENV_DUMP_LOADER .
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.El
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.Sh RETURN VALUES
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The
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.Fn kenv
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system call returns 0 if successful in the case of
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.Dv KENV_SET
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and
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.Dv KENV_UNSET ,
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and the number of bytes copied into
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.Fa value
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in the case of
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.Dv KENV_DUMP
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and
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.Dv KENV_GET .
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If an error occurs, a value of \-1 is returned and
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the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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The
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.Fn kenv
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa action
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argument
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is not a valid option, or the length of the
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.Fa value
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is less than 1 for a
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.Dv KENV_SET .
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.It Bq Er ENOENT
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No value could be found for
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.Fa name
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for a
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.Dv KENV_GET
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or
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.Dv KENV_UNSET .
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.It Bq Er ENOENT
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The requested environment is not available for a
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.Dv KENV_DUMP_LOADER
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or
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.Dv KENV_DUMP_STATIC .
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The kernel is configured to destroy these environments by default.
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.It Bq Er EPERM
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A user other than the superuser attempted to set or unset a kernel
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environment variable.
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.It Bq Er EPERM
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A user other than the superuser attempted to get a variable from or dump the
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kernel environment, and the
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.Va security.bsd.unprivileged_kenv_read
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sysctl is set to 0.
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.It Bq Er EFAULT
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A bad address was encountered while attempting to copy in user arguments
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or copy out value(s).
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.It Bq Er ENAMETOOLONG
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The
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.Fa name
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or the
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.Fa value
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is longer than
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.Dv KENV_MNAMELEN
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or
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.Dv KENV_MVALLEN
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characters, respectively, or
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.Fa len
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did not include the NUL terminator for a
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.Dv KENV_SET .
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.El
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.Sh SEE ALSO
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.Xr kenv 1
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.An Chad David Aq Mt [email protected] .
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.Pp
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The
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.Fn kenv
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system call was written by
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.An Maxime Henrion Aq Mt [email protected] .
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