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KENV(2) 		       System Calls Manual			 KENV(2)

NAME
     kenv -- kernel environment

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <kenv.h>

     int
     kenv(int action, const char *name, char *value, int len);

DESCRIPTION
     The  kenv()  system call manipulates kernel environment variables.  It sup-
     ports the well known userland actions of getting, setting and unsetting en-
     vironment variables, as well as the ability to dump all of the  entries  in
     the kernel environment.

     The action argument can be one of the following:

     KENV_GET	       Get  the  value of the variable with the given name.  The
		       size of the value buffer is given by len, which should be
		       at least KENV_MVALLEN + 1 bytes to avoid  truncation  and
		       to ensure NUL termination.

     KENV_SET	       Set or add a variable.  The name and value are limited to
		       KENV_MNAMELEN  and  KENV_MVALLEN characters, respectively
		       (not including the NUL terminator.) The len argument  in-
		       dicates	the length of the value and must include the NUL
		       terminator.  This option is only available to  the  supe-
		       ruser.

     KENV_UNSET        Unset  the  variable  with the given name.  The value and
		       len arguments are ignored.  This option is only available
		       to the superuser.

     KENV_DUMP	       Dump as much of the dynamic kernel  environment	as  will
		       fit  in	value,	whose size is given in len.  If value is
		       NULL, kenv() will return the number of bytes required  to
		       copy out the entire environment.  The name is ignored.

     KENV_DUMP_LOADER  Dump  the  static environment provided by loader(8), with
		       semantics identical to  KENV_DUMP.   Duplicate  and  mal-
		       formed  variables  originally present in this environment
		       are discarded by the kernel and will not  appear  in  the
		       output.

     KENV_DUMP_STATIC  Dump  the  static  environment defined by the kernel con-
		       fig(5).	The semantics are identical to KENV_DUMP_LOADER.

RETURN VALUES
     The kenv() system call returns 0 if successful in the case of KENV_SET  and
     KENV_UNSET,  and  the  number  of	bytes  copied  into value in the case of
     KENV_DUMP and KENV_GET.  If an error occurs, a value of -1 is returned  and
     the global variable errno is set to indicate the error.

ERRORS
     The kenv() system call will fail if:

     [EINVAL]		The action argument is not a valid option, or the length
			of the value is less than 1 for a KENV_SET.

     [ENOENT]		No  value  could  be  found  for  name for a KENV_GET or
			KENV_UNSET.

     [ENOENT]		The  requested	environment  is  not  available  for   a
			KENV_DUMP_LOADER  or  KENV_DUMP_STATIC.   The  kernel is
			configured to destroy these environments by default.

     [EPERM]		A user other than the superuser attempted to set or  un-
			set a kernel environment variable.

     [EFAULT]		A  bad	address was encountered while attempting to copy
			in user arguments or copy out value(s).

     [ENAMETOOLONG]	The name or the value is longer  than  KENV_MNAMELEN  or
			KENV_MVALLEN  characters,  respectively,  or len did not
			include the NUL terminator for a KENV_SET.

SEE ALSO
     kenv(1)

AUTHORS
     This manual page was written by Chad David <davidc@FreeBSD.org>.

     The kenv() system call was written by Maxime Henrion <mux@FreeBSD.org>.

FreeBSD ports 15.quarterly	  June 20, 2021 			 KENV(2)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=kenv&sektion=2&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

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