MII-DIAG(8) System Manager's Manual MII-DIAG(8)
mii-diag - Network adapter control and monitoring
This manual page documents briefly the mii-diag network adapter control and monitoring command. Addition documentation is available from
This mii-diag command configures, controls and monitors the transceiver management registers for network interfaces, and configures driver
operational parameters. For transceiver control mii-diag uses the Media Independent Interface (MII) standard (thus the command name). It
also has additional Linux-specific controls to communicate parameters such as message enable settings and buffer sizes to the underlying
The MII standard defines registers that control and report network transceiver capabilities, link settings and errors. Examples are link
speed, duplex, capabilities advertised to the link partner, status LED indications and link error counters.
The mii-diag command supports both single character and long option names. Short options use a single dash ('-') in front of the option
character. For options without parameters, multiple options may be concatenated after a single dash. Long options are prefixed by two
dashes ('--'), and may be abbreviated with a unique prefix. A long option may take a parameter of the form --arg=param or --arg param.
A summary of options is as follows.
-A, --advertise <speed|setting>
-F, --fixed-speed <speed|setting>
Speed is one of: 100baseT4, 100baseTx, 100baseTx-FD, 100baseTx-HD, 10baseT, 10baseT-FD, 10baseT-HD. For more precise control an
explicit numeric register setting is also allowed.
Show the status of all interfaces. This option is not recommended with any other option, especially ones that change settings.
Return exit status 2 if there is no link beat.
-D Increase the debugging level. This may be used to understand the actions the command is taking.
Show driver-specific parameters.
-G, --set-parameters value[,value...]
Set driver-specific parameters. Set a adapter-specific parameters. Parameters are comma separated, with missing elements retaining
the existing value.
-v Increase the verbosity level. Additional "-v" options increase the level further.
-V Show the program version information.
Continuously monitor the transceiver and report changes.
-? Emit usage information.
Calling the command with just the interface name (which defaults to capabilities, configuration and current status.
The '--monitor' option allows scripting link beat changes.
This option is similar to --watch, but with lower overhead and simplified output. It polls the interface only once a second and the output
format is a single line per link change with three fixed words
<unknown|down||negotiating|up> <STATUS> <PARTNER-CAP>
Example output: mii-diag --monitor eth0
down 0x7809 0x0000
negotiating 0x7829 0x45e1
up 0x782d 0x45e1
down 0x7809 0x0000
This may be used as
mii-diag --monitor eth0 |
while read linkstatus bmsr linkpar; do
case $linkstatus in
up) ifup eth0 ;;
down) ifdown eth0 ;;
It may be useful to shorten the DHCP client daemon timeout if it does not receive an address by adding the following setting to
/etc/sysconfig/network: DHCPCDARGS="-t 3"
Addition documentation is available from http://scyld.com/diag/index.html.
The --all-interfaces option is quirky. There are very few settings that are usefully applied to all interfaces.
The manual pages, diagnostic commands, and many of the underlying Linux network drivers were written by Donald Becker for the Scyld
Beowulf(tm) cluster system.
Scyld Beowulf September 9, 2003 MII-DIAG(8)