mii-tool(8) — Linux manual page

MII-TOOL(8)        Linux System Administrator's Manual        MII-TOOL(8)

NAME         top

       mii-tool - view, manipulate media-independent interface status

SYNOPSIS         top

       mii-tool [-v, --verbose] [-V, --version] [-R, --reset] [-r,
       --restart] [-w, --watch] [-l, --log] [-A, --advertise=media,...]
       [-F, --force=media] [-p, --phy=addr] interface ...

DESCRIPTION         top

       This utility checks or sets the status of a network interface's
       Media Independent Interface (MII) unit.  Most fast ethernet
       adapters use an MII to autonegotiate link speed and duplex
       setting.

       Most intelligent network devices use an autonegotiation protocol
       to communicate what media technologies they support, and then
       select the fastest mutually supported media technology.  The -A or
       --advertise options can be used to tell the MII to only advertise
       a subset of its capabilities.  Some passive devices, such as
       single-speed hubs, are unable to autonegotiate.  To handle such
       devices, the MII protocol also allows for establishing a link by
       simply detecting either a 10baseT or 100baseT link beat.  The -F
       or --force options can be used to force the MII to operate in one
       mode, instead of autonegotiating.  The -A and -F options are
       mutually exclusive.

       The default short output reports the negotiated link speed and
       link status for each interface.

OPTIONS         top

       -v, --verbose
              Display more detailed MII status information.  If used
              twice, also display raw MII register contents.
              Alert: If used three times, will force reading all MII
              registers, including non standard ones. It's not guaranteed
              any valid answer from PHY while PHY communication can even
              hang.  With driver e1000e will fail while reading register
              0x07.

       -V, --version
              Display program version information.

       -R, --reset
              Reset the MII to its default configuration.

       -r, --restart
              Restart autonegotiation.

       -w, --watch
              Watch interface(s) and report changes in link status.  The
              MII interfaces are polled at one second intervals.

       -l, --log
              Used with -w, records link status changes in the system log
              instead of printing on standard output.

       -F media, --force=media
              Disable autonegotiation, and force the MII to either
              100baseTx-FD, 100baseTx-HD, 10baseT-FD, or 10baseT-HD
              operation.

       -A media,..., --advertise=media,...
              Enable and restart autonegotiation, and advertise only the
              specified media technologies.  Multiple technologies should
              be separated by commas.  Valid media are 100baseT4,
              100baseTx-FD, 100baseTx-HD, 10baseT-FD, and 10baseT-HD.

       -p addr, --phy=addr
              Override the MII address provided by kernel with value
              addr.

DIAGNOSTICS         top

       SIOCGMIIPHY on 'eth?' failed: Invalid argument
              If the interface is not running (up), kernel will refuse to
              report its link state.

       SIOCGMIIPHY on 'eth?' failed: Operation not permitted
              Most kernels restrict access to root.

       SIOCGMIIPHY on 'eth?' failed: No such device
              This error is shown, if the kernel does not know about the
              named device.

       SIOCGMIIPHY on 'eth?' failed: Operation not supported
              The interface in question does not support MII queries.
              Most likely, it does not have MII transceivers, at all.

AUTHORS         top

       David Hinds - [email protected]
       Donald Becker - [email protected]
       Bernd Eckenfels - [email protected]

SEE ALSO         top

       http://net-tools.sourceforge.net - Homepage of the net-tools
       project

COLOPHON         top

       This page is part of the net-tools (networking utilities) project.
       Information about the project can be found at 
       ⟨http://net-tools.sourceforge.net/⟩.  If you have a bug report for
       this manual page, see ⟨http://net-tools.sourceforge.net/⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨git://git.code.sf.net/p/net-tools/code⟩ on 2025-08-11.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2025-05-17.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there is
       a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       [email protected]

net-tools                       2013-02-15                    MII-TOOL(8)

HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.