Want to know how and why Linux names its Ethernet adapters ?

I picked this up from a Raspberry Pi forum, whilst trying to get a USB wireless adapter to work with my Pi.

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I cannot tell for certain why your device gets renamed from wlan0 to wlan1 but it might be worth looking into "/etc/udev/rules.d/70-persistent-net.rules". This file is created by udev to store the names of network interfaces and keep them consistent throughout the system. Udev should automatically put a comment before each rule, saying which driver is responsible for the interface.

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I'd not looked into this before, but had wondered why, on one of my Red Hat Enterprise Linux VMs, the Ethernet card always comes up as eth4 rather than eth0.

When I checked the file: -

$ cat /etc/udev/rules.d/70-persistent-net.rules

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x8086:0x100e (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="08:00:27:87:e2:dc", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:07:2f:73", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:d1:94:31", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:60:44:f2", ATTR{type}=="1", KERNEL=="eth*", NAME="eth3"

# PCI device 0x8086:0x100f (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:9c:4a:af", ATTR{type}=="1", KERNEL=="eth*", NAME="eth4"

I'm guessing that the MAC ( Media Access Control ) address has changed since I first spun up the VM, perhaps meaning that Linux has kindly created a new interface - eth4 - for the "new" MAC address.

I imagine that, if I wanted to change it back to eth0, I could simply "hack" this file, perhaps removing the first four entries, and renaming eth4 to eth0 on the one remaining line.

Still, it's good to know why it happens ….