I tried to install Jessie on a Lenovo X220 using netinst on USB
flash drive, without Ethernet connection, but with the non-free
iwlwifi drivers .deb on an SD card (either internal slot or USB
adaptor).

After the very early step of selecting the keyboard layout, the
installer seems to try to start X or something, but seems to fail.
The screen flashes "for ever" and installation cannot be
continued.

Workaround:

If I use Ethernet instead of Wifi and do not use the SD card,
the installation continues.

Btw, debian-7.8.0-amd64-netinst.iso shows the same behaviour.

Ok, that's *really* weird. I've been doing test installations
regularly on various X220 machines for *ages* and never seen this. Is
there anything special at all about your SD card? Is the machine
locked, or can you get to logs?

Hi,

W. Martin Borgert <debacle@debian.org> (2015-07-16):

Are you using the text mode installer or the graphical installer?
There's no X in the former, and X is started at the very beginning
(after syslinux prompt, but before any questions are asked) in the
latter.

Mraw,
KiBi.

Text mode.

You are right, it is not X. Something else that makes the screen
flash. Flashing frequency is about 2 Hz, way to fast for failing
X :~) I can see two ps entries with permanently changing pids:

{debian-installe} /bin/sh /sbin/debian-installer
/usr/share/debconf/frontend -- /bin/debconf-get debian-installer/theme

remember the 4th console :~)

It says more or less:

Jul 16 19:28:10 kernel: [  110.811848] main-menu[9666]: segfault at 1 ip 00007f16b6dccd8 sp 00007f
fe7cd124e8 error 4 in libc-2.19.so[7f1202d825000+19f000]

The SD card had - according to GParted a small unallocated area
first, and then an almost 4 GB fat32 partition. I changed this
to one partition and the problem is gone!

Thanks for the hint with the SD card - it was the real culprit.