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>.