hi,

I am starting guest OS (linux) using below command.

emu-system-x86_64 -m 2048 -nographic -cdrom guestOS.iso -hda vdisk_1.img -serial telnet:localhost:8002,server,nowait

When guest OS boot up, i see below interfaces with ifconfig. My question s there is no NIC devices provided to guest os by qemu, then how would guest OS be able to initialize these interfaces? Thanks.


(none)(shell)> ifconfig
eth0 Link encap:Ethernet HWaddr 00:00:00:00:01:01
inet addr:127.1.1.1 Bcast:127.1.255.255 Mask:255.255.0.0
inet6 addr: fe80::200:ff:fe00:101/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

eth1 Link encap:Ethernet HWaddr 52:54:00:12:34:56
inet6 addr: fe80::5054:ff:fe12:3456/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:1005 (1005.0 b)
Interrupt:11

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.255.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:262 errors:0 dropped:0 overruns:0 frame:0
TX packets:262 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:20652 (20.1 KiB) TX bytes:20652 (20.1 KiB)

The qemu-system-x86_64 has many start up options that define the guest environment. In your example you did not provide any "-net" options. Search for -net on the following link for a better understanding.

http://wiki.qemu.org/download/qemu-doc.html

my question is qemu did not provide any NIC cards for guest OS, then where does guest OS get eth0, eth1 from?

It depends on the distro. Init scripts, udev rules or network managers can create interfaces.