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I am using the follwing to find the mtu value

ifconfig | grep mtu
eno17832: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9000
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536

but in my bash script we want to know exactly the MTU value

so we can use this

MTU_VAL=` ifconfig | grep mtu | head -1 | awk '{print $NF}' `

but this may be risky and no so elegant

please let me know if we can capture the MTU for sure ?

  • exactly the MTU value - each ethernet interface has its own mtu value – RomanPerekhrest Apr 24 '18 at 12:35
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Most tools leverage information present in /proc or /sys, concerning ifconfig I'd go with /sys/class/net/<interface>/* files:

To get mtu for all interfaces but loopback (lo) this would work:

cat /sys/class/net/[^l][^o]*/mtu

The exclusion is done by shell globing, anything not starting with l then o is expanded and then the mtu file within it is read. If there's only one interface other than loopback it will return its mtu as a single value, usable in script with $() to put the output in a variable.

To answer the comment:

$ awk '{split(FILENAME,arr,"/"); print arr[5],$1}' /sys/class/net/*/mtu
ens160 1500
lo 65536

Same pattern match as above to exclude lo if needed (I've kept it here to showcase multiple interface output).

  • this is nice way , can we get the interface name and mtu value on each line? – yael Apr 24 '18 at 13:15
  • @yael this highly sounds like an XY problem, what are you willing to do with this information ? – Tensibai Apr 24 '18 at 13:25
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Read from its config value directly.

MTU_VAL=$(< /sys/class/net/<replace-with-interface-name>/mtu)

Just replace <replace-with-interface-name> with the interface-name you want its MTU.

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