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 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.

       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  indicates  the
                   length  of  the  value and must include the NUL terminator.  This option is only available to
                   the superuser.

       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 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.

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.

       [EPERM]            A user other than the superuser  attempted  to  set  or  unset  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>.

Debian                                          February 20, 2017                                        KENV(2)