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.\" $FreeBSD: head/lib/libc/sys/kenv.2 267774 2014-06-23 08:25:03Z bapt $
.\"
.Dd April 17, 2002
.Dt KENV 2
.Os
.Sh NAME
.Nm kenv
.Nd kernel environment
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In kenv.h
.Ft int
.Fn kenv "int action" "const char *name" "char *value" "int len"
.Sh DESCRIPTION
The
.Fn kenv
system call manipulates kernel environment variables.
It supports the well known userland actions of getting, setting and unsetting
environment variables, as well as the ability to dump all of the entries in
the kernel environment.
.Pp
The
.Fa action
argument can be one of the following:
.Bl -tag -width ".Dv KENV_UNSET"
.It Dv KENV_GET
Returns the value associated with the named kernel environment variable.
If the variable is not found, \-1 is returned and
the global variable
.Va errno
is set to
.Er ENOENT .
Only the number of bytes available in
.Fa value
are copied out.
.It Dv KENV_SET
Sets or adds a new kernel environment variable.
This option is only available to the superuser.
.It Dv KENV_UNSET
Unsets the kernel environment variable
.Fa name .
If the variable does not exist, \-1 is returned and
the global variable
.Va errno
is set to
.Er EINVAL .
This option is only available to the superuser.
.It Dv KENV_DUMP
Dumps as much of the kernel environment as will fit in
.Fa value .
If
.Fa value
is
.Dv NULL ,
.Fn kenv
will return the number of bytes required to copy out the entire environment.
.El
.Pp
The
.Fa name
argument is the name of the environment variable to be affected.
In the case of
.Dv KENV_DUMP
it is ignored.
.Pp
The
.Fa value
argument contains either the value to set the environment variable
.Fa name
to in the case of
.Dv KENV_SET ,
or it points to the location where
.Fn kenv
should copy return data to in the case of
.Dv KENV_DUMP
and
.Dv KENV_GET .
If
.Fa value
is
.Dv NULL
in the case of
.Dv KENV_DUMP ,
.Fn kenv
will return the number of bytes required to copy out the entire environment.
.Pp
The
.Fa len
argument indicates how many bytes of storage
.Fa value
points to.
.Sh RETURN VALUES
The
.Fn kenv
system call returns 0 if successful in the case of
.Dv KENV_SET
and
.Dv KENV_UNSET ,
and the number of bytes copied into
.Fa value
in the case of
.Dv KENV_DUMP
and
.Dv KENV_GET .
If an error occurs, a value of \-1 is returned and
the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn kenv
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa action
argument
is not a valid option, or the length of the
.Fa value
is less than 1 for a
.Dv KENV_SET .
.It Bq Er ENOENT
no value could be found for
.Fa name
for a
.Dv KENV_SET
or
.Dv KENV_UNSET .
.It Bq Er EPERM
a user other than the superuser attempted to set or unset a kernel
environment variable.
.It Bq Er EFAULT
bad address was encountered while attempting to copy in user arguments,
or copy out value(s).
.It Bq Er ENAMETOOLONG
the name of a variable supplied by the user is longer than
.Dv KENV_MNAMELEN
or the value of a variable is longer than
.Dv KENV_MVALLEN .
.El
.Sh SEE ALSO
.Xr kenv 1
.Sh AUTHORS
.An -nosplit
This manual page was written by
.An Chad David Aq Mt davidc@FreeBSD.org .
.Pp
The
.Fn kenv
system call was written by
.An Maxime Henrion Aq Mt mux@FreeBSD.org .