NAME
    Alien::SNMP - Alien package for the Net-SNMP library

SYNOPSIS
     use Alien::SNMP;
     # then it's just like SNMP.pm
 
     say Alien::SNMP->bin_dir;
     # where the net-snmp apps (snmptranslate, etc) live

DESCRIPTION
    Alien::SNMP downloads and installs the Net-SNMP library and associated
    perl modules.

    The library is built with the following options:

    "--disable-agent"
    "--disable-manuals"
    "--disable-scripts"
    "--disable-mibs"
    "--enable-ipv6"
    "--with-mibs="""
    "--with-perl-modules"
    "--disable-embedded-perl"
    "--enable-blumenthal-aes"
    "--with-defaults"

  macOS
    Build this with a Homebrew or perlbrew perl. Apple's /usr/bin/perl is
    not a supported target: it is frozen at whatever version macOS shipped,
    its directories need root, and Apple has deprecated the runtime.
    Continuous integration covers Homebrew perl on both Intel and Apple
    Silicon.

    If a bare "perl" on your "PATH" still resolves to /usr/bin/perl,
    "Makefile.PL" aborts with "Can't locate Alien/Build/MM.pm". Run it with
    the full path to the perl you mean.

BACKGROUND
    Net-SNMP's Perl modules live in the Net-SNMP source tree; they are not a
    separately maintained CPAN distribution. The standalone "SNMP" release
    on CPAN is 5.0404, whose version number encodes the Net-SNMP 5.4.4
    release it was taken from. This distribution instead installs the "SNMP"
    module out of the Net-SNMP tarball it builds and pins, so the Perl
    module and the C library beneath it always come from the same upstream
    release. That coupling matters, because the XS is compiled against one
    specific libnetsnmp, and it is what keeps the Perl side level with the
    library rather than years behind it.

    Three kinds of user need that.

    Anyone installing outside the system perl
        The Perl modules in a distribution's "net-snmp" package are built
        for the system perl and installed into system directories, so under
        perlbrew, local::lib, or any "INSTALL_BASE" prefix they are simply
        not on @INC. This distribution builds them with the perl that is
        running the build and installs them wherever that perl's install
        target points. See "BUNDLED PERL MODULES".

    Anyone parsing large MIB collections
        Older Net-SNMP had fixed ceilings in the MIB parser: a maximum
        number of Textual Conventions, and a maximum number of imports per
        module. Large vendor MIB collections reached them, which is why
        patched Net-SNMP builds were once needed for MIB development. Both
        limits are gone as of Net-SNMP 5.9, where the Textual Convention
        list grows on demand and "MAX_IMPORTS" is 512. A stock build from
        this distribution needs no patching for that work.

    Anyone shelling out to the Net-SNMP tools
        The command line utilities are built here too, from the same source,
        and can be put ahead of the system ones on "PATH". See "COMMAND LINE
        UTILITIES".

BUNDLED PERL MODULES
    The Net-SNMP source ships the "SNMP" and "NetSNMP::*" XS modules. They
    are built against the library built here, by the same perl that is
    building this distribution, and are installed along with it. A bare "use
    SNMP;" therefore works, and they follow whatever installation target you
    give Alien::SNMP itself ("INSTALL_BASE", "PREFIX", "DESTDIR",
    local::lib).

    They resolve "libnetsnmp" from this Alien's share dir, so they coexist
    with an operating system "net-snmp" package: system tools keep using the
    system library, while these modules use ours. That is arranged two ways:
    Net-SNMP bakes the share dir into the XS modules' run-path, and this
    module additionally preloads the share copy at use-time. Note that the
    run-path is emitted as "DT_RUNPATH", which "LD_LIBRARY_PATH" takes
    precedence over; the preload is what makes the choice robust in that
    case.

    On macOS the mechanism differs but the outcome does not: the XS modules
    record "libnetsnmp" by its absolute path in the installed share dir, so
    that is the copy they load.

  Shadowing an operating system packaged SNMP.pm
    Some operating systems ship Net-SNMP's Perl modules as a package of
    their own, installed into the system perl's vendor directories.
    Installing Alien::SNMP into that same perl, which is what happens when
    it is installed as root outside perlbrew or local::lib, puts our copy in
    the site directories. Those precede the vendor ones in @INC, so ours
    answers "use SNMP;" for every script that perl runs.

    Nothing is overwritten. The two copies live in different directories,
    and removing Alien::SNMP brings the operating system packaged one back.
    But the substitution is silent, and our copy looks in different places
    than the operating system packaged one did:

    MIB files
        The operating system packaged module searches the system MIB
        directory, usually /usr/share/snmp/mibs. Ours does not. See "MIBS".

    snmp.conf
        The operating system packaged module reads /etc/snmp/snmp.conf,
        where a site keeps defaults such as "defVersion", "defCommunity",
        "mibdirs" and "mibs". Ours reads snmp.conf from its own share
        directory and from ~/.snmp, never from /etc/snmp, so those defaults
        stop applying. Set "SNMPCONFPATH" to the directories you want
        searched to get them back.

    Neither change reports anything: symbolic names quietly stop resolving
    and site defaults quietly stop being read. Installing into a perlbrew or
    local::lib perl raises neither question, because nothing is shadowed.

MIBS
    No MIB files are shipped, because Net-SNMP is configured here with
    "--disable-mibs" and "--with-mibs=""". Out of the box both the Perl
    modules and the command line tools work in numeric OIDs, and
    "snmptranslate" reports "Cannot find module".

    The system MIB directory is not consulted either. The default search
    path is ~/.snmp/mibs plus a directory inside this distribution's share,
    and nothing else, whatever the operating system may have installed
    elsewhere.

    That is a matter of supplying MIBs, not a missing capability. Symbolic
    names resolve normally, in both directions, once a collection is on the
    search path. Put one there with the "-M" option or the "MIBDIRS"
    environment variable, or place files in ~/.snmp/mibs, which is on the
    default path:

     $ MIBDIRS=/path/to/mibs snmptranslate .1.3.6.1.2.1.1.3.0
     SNMPv2-MIB::sysUpTime.0

    From Perl, "SNMP::addMibDirs" and "SNMP::loadModules" do the same job.
    Either way that covers the modules Net-SNMP loads by default; anything
    outside that list also needs naming, with "-m" or the "MIBS" environment
    variable.

  The MIB index files are gone
    Net-SNMP 5.9 removed the on-disk MIB index cache. It no longer writes or
    reads the ".index" files older versions left inside MIB directories, nor
    the numbered files under "SNMP_PERSISTENT_DIR", and that variable now
    has no bearing on MIB indexing at all. Parsing is unaffected:
    "snmptranslate", "SNMP::addMibDirs" and "SNMP::loadModules" behave as
    they always did, and directories are simply rescanned each run instead
    of being read from a cache.

    What is gone is any way to ask Net-SNMP which file defines a given
    module. It still tracks that internally but exposes no accessor, so code
    that located a module's file by reading an index directory will find
    nothing there. Derive the mapping from the files instead, following
    Net-SNMP's own rule from add_mibfile() in snmplib/parse.c: a file
    defines a module when its first token is a label and its second is
    "DEFINITIONS", and that first token is the module name. Reading the head
    of each candidate file until "DEFINITIONS" appears is enough to build
    the map.

    Two things trip up a hand-rolled version. Strip "--" comments before
    looking for "DEFINITIONS", or a mention of it in a file's comment header
    ends the read early; note too that an ASN.1 comment ends at a second
    "--" as well as at end of line. And do not derive the module from the
    file name: SNMPv2-MIB.txt does contain "SNMPv2-MIB", so that shortcut
    passes on the common case and then fails on vendor MIBs, where
    CISCO-90-MIB.my defines "Cisco90Series-MIB".

    Building the map opens every file in the collection, so cache it if you
    need it often.

COMMAND LINE UTILITIES
    The build also produces the Net-SNMP client tools, "snmpget",
    "snmpwalk", "snmpbulkwalk", "snmptranslate", "snmptable" and the rest,
    from the same pinned source as the library and the Perl modules.
    "--disable-agent" means there is no "snmpd"; these are the client side.
    "bin_dir" returns the directory holding them, so a program that shells
    out can use them in preference to whatever the operating system ships,
    or on a host that ships none:

     use Alien::SNMP;
     use Env qw( @PATH );
     unshift @PATH, Alien::SNMP->bin_dir;

     my $uptime = `snmpget -v2c -c public $host 1.3.6.1.2.1.1.3.0`;

    They read MIBs and snmp.conf from this distribution's own directories
    rather than from /usr/share/snmp/mibs and /etc/snmp, so putting
    "bin_dir" first on "PATH" changes both for anything that runs from
    there. See "Shadowing an operating system packaged SNMP.pm".

    Their options and output formats are Net-SNMP's own and are documented
    at <http://www.net-snmp.org/docs/man/>. This distribution builds with
    "--disable-manuals", so it installs no man pages of its own for them.

  Which libnetsnmp the utilities load
    Each utility records this distribution's share directory as its
    run-path, so it finds our "libnetsnmp" without any help from you, and
    coexists with a system Net-SNMP package. The one thing that overrides a
    run-path is "LD_LIBRARY_PATH", an environment variable that is unset on
    most systems and that "echo $LD_LIBRARY_PATH" will show you. If it is
    set, and names a directory holding another "libnetsnmp" of the same
    major version, that copy is loaded instead of ours. "delete local
    $ENV{LD_LIBRARY_PATH};" around the call rules that out.

METHODS
  bin_dir
     my $bin_dir = Alien::SNMP->bin_dir;

    Returns the location of the net-snmp apps (snmptranslate, etc). See
    "COMMAND LINE UTILITIES".

  cflags
     my $cflags = Alien::SNMP->cflags;

    Returns the C compiler flags.

  libs
     my $libs = Alien::SNMP->libs;

    Returns the linker flags.

SEE ALSO
    Alien
    Alien::Base
    SNMP
        The Perl5 'SNMP' Extension Module for the Net-SNMP SNMP package.
        Depends on libnetsnmp and the corresponding version is installed
        along with the C library.

AUTHOR
    Eric A. Miller, "<emiller at cpan.org>"

LICENSE AND COPYRIGHT
    Copyright 2026 Eric A. Miller.

    This program is distributed under the (Revised) BSD License:
    <http://www.opensource.org/licenses/BSD-3-Clause>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

    * Redistributions of source code must retain the above copyright notice,
    this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.

    * Neither the name of Eric A. Miller's Organization nor the names of its
    contributors may be used to endorse or promote products derived from
    this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
    IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
    TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
    OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
    EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
    LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
    NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

