How can I show the old eth0 names and also rename network interfaces in debian 9 stretch?
Assuming that you have just installed your debian 9 stretch.
1) For reverting back the old names for the interfaces do:
nano /etc/default/grub
edit the line GRUB_CMDLINE_LINUX="" to GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0"
then launch a grub-mkconfig for apply the changes inside the bootloader
grub-mkconfig -o /boot/grub/grub.cfg
You need a reboot after that.
2) For renaming the interfaces use:
For just a temporary modification take a look at the @xhienne answer.
For a permanent modification:
Start by creating / editing the /etc/udev/rules.d/70-persistent-net.rules file.
nano /etc/udev/rules.d/70-persistent-net.rules
And insert inside lines like:
# interface with MAC address "00:0c:30:50:48:a1" will be assigned "eth0"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:30:50:48:a1", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
# interface with MAC address "00:0c:30:50:48:ab" will be assigned "eth1"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:30:50:48:ab", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"
If you want to assign for example a name like wan0 to eth0 you can use given my example:
# interface with MAC address "00:0c:30:50:48:a1" will be assigned "eth0"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:30:50:48:a1", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="wan0"
After the next reboot or using service networking restart you should see the changes applied.
EXTRA: Remember that after all this modifications you have to edit your /etc/network/interfaces file replacing the old interfaces names with the new ones!
EXTRA: If you want to know what MAC address your interfaces have, just do a
ip addr show
and look under the link/ section.
For question 1) see user3450548's answer. For question 2) you can give any name you want to an interface with iproute2:
ip link set ens33 down # Else you will get "Device or resource busy"
ip link set ens33 name eth0