I noticed when my G5 does this, when I turn power on, the G5 "reboots" like it does when you have updated it with the programming software (the ...... screen shows up).
It looks like the G5 runs an OS and the OS is embedded linux. It might be that the linux OS crashes and needs to reboot. Why all the LEDs turn on, I don't know...
This is how I determined that the G5 is running linux: On a linux machine (haven't tried it on a Windows machine), the G5 shows up as an Ethernet interface when connected via the USB cable. My particular G5 has an IP address of 10.10.0.6. It also appears that you can SSH into the G5 if you know the username and password (which I do not).
To verify that the G5 is running linux, you can use the nmap utility's OS detection feature on your linux PC:
>sudo nmap -O 10.10.0.6
this is the result:
Starting Nmap 7.01 (
https://nmap.org ) at 2017-01-19 11:48 EST
Nmap scan report for 10.10.0.6
Host is up (0.000010s latency).
Not shown: 998 closed ports
PORT STATE SERVICE
22/tcp open ssh
8200/tcp open trivnet1
Device type: general purpose
Running: Linux 3.X
OS CPE: cpe:/o:linux:linux_kernel:3
OS details: Linux 3.12 - 3.19, Linux 3.8 - 3.19
Network Distance: 0 hops
So it looks like the G5 is using a Linux 3.X kernel and the SSH port 22 is open...
On my machine doing an
>ifconfig
the G5 shows up as:
enp0s20u7 Link encap:Ethernet HWaddr be:6e:3b:3e:6f:6b
inet addr:10.10.0.6 Bcast:10.10.255.255 Mask:255.255.0.0
inet6 addr: fe80::28a3:e00a:3adf:d029/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2 errors:0 dropped:0 overruns:0 frame:0
TX packets:127 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:594 (594.0 B) TX bytes:25988 (25.9 KB)
You can ping the G5 too:
ping 10.10.0.6
PING 10.10.0.6 (10.10.0.6) 56(84) bytes of data.
64 bytes from 10.10.0.6: icmp_seq=1 ttl=64 time=0.027 ms
64 bytes from 10.10.0.6: icmp_seq=2 ttl=64 time=0.046 ms
64 bytes from 10.10.0.6: icmp_seq=3 ttl=64 time=0.024 ms