Ich glaube, ich habe einen Weg gefunden, ohne »Interims-Update« auszukommen:
OS: FW: 0.7.4~118
HW: Westmere E56xx/L56xx/X56xx (Nehalem-C)
root@33332-FWTest-f26e:~# cd /tmp
root@33332-FWTest-f26e:/tmp# wget http://firmware.4830.org/rawhide/sysupgrade/gluon-ffgt-0.7.9~107-x86-kvm-sysupgrade.img.gz
Connecting to firmware.4830.org ([2a06:e881:1700:1:400:c0ff:fefb:e216]:80)
gluon-ffgt-0.7.9~107 100% |*******************************| 4723k 0:00:00 ETA
root@33332-FWTest-f26e:/tmp# head -6 /etc/config/system
config system
option timezone 'CET-1CEST,M3.5.0,M10.5.0/3'
option hostname '33332-FWTest-f26e'
config timeserver 'ntp'
root@33332-FWTest-f26e:/tmp# ip addr show br-wan
6: br-wan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
link/ether 52:55:00:14:f2:6e brd ff:ff:ff:ff:ff:ff
inet 192.168.122.218/24 brd 192.168.122.255 scope global br-wan
valid_lft forever preferred_lft forever
inet6 fe80::5055:ff:fe14:f26e/64 scope link
valid_lft forever preferred_lft forever
root@33332-FWTest-f26e:/tmp# sysupgrade -v gluon-ffgt-0.7.9~107-x86-kvm-sysupgra
de.img.gz
Saving config files...
[…]
Upgrade completed
Rebooting system...
packet_write_wait: Connection to 192.168.122.218: Broken pipe
Okay, 0.7.4~118 auf 0.7.9~107 aktualisiert. Und, tut das?
wusel@ysabell:~$ ssh root@192.168.122.218
sh: /usr/bin/xauth: not found
[…]
OS: Chaos Calmer, r49389 FW: 0.7.9~107
HW: Westmere E56xx/L56xx/X56xx (Nehalem-C)
root@33332-FWTest-f26e:~# ip addr show br-wan
7: br-wan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
link/ether 52:55:00:14:f2:6e brd ff:ff:ff:ff:ff:ff
inet 192.168.122.218/24 brd 192.168.122.255 scope global br-wan
valid_lft forever preferred_lft forever
inet6 fe80::5055:ff:fe14:f26e/64 scope link
valid_lft forever preferred_lft forever
root@33332-FWTest-f26e:~# head -6 /etc/config/system
config system
option timezone 'CET-1CEST,M3.5.0,M10.5.0/3'
option hostname '33332-FWTest-f26e'
option staticwanmac '52:55:00:14:f2:6e'
Ja! 
Okay, und wenn man von 0.7.9 in den Config-Mode geht?
root@33332-FWTest-f26e:~# uci set gluon-setup-mode.@setup_mode[0].enabled=1
root@33332-FWTest-f26e:~# uci commit
root@33332-FWTest-f26e:~# uci get gluon-setup-mode.@setup_mode[0].enabled
1
root@33332-FWTest-f26e:~# reboot
root@33332-FWTest-f26e:~# Connection to 192.168.122.218 closed.
wusel@ysabell:~$ telnet 192.168.122.218
Trying 192.168.122.218...
Connected to 192.168.122.218.
[…]
OS: Chaos Calmer, r49389 FW: 0.7.9~107
HW: Westmere E56xx/L56xx/X56xx (Nehalem-C)
root@33332-FWTest-f26e:/# Connection closed by foreign host.
wusel@ysabell:~$ ssh root@192.168.122.218 uptime
sh: /usr/bin/xauth: not found
02:47:12 up 0 min, load average: 0.00, 0.00, 0.00
wusel@ysabell:~$
Im Config-Mode im Web den Branch auf “rawhide” gesetzt, durchgeklickt, es kam zum Reboot … und der Knoten blieb bei seiner MAC/seiner IP.
0.7.9~107 ist auf http://firmware.4830.org/ verfügbar; bitte, wo möglich, gegen 0.7.4~118- und 0.7.5~29-Basisfirmware testen …