KENV(2)                   FreeBSD 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
     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 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 malformed 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
                           config(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
                        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>.

FreeBSD 13.1-RELEASE-p6          June 20, 2021         FreeBSD 13.1-RELEASE-p6