That worked for me too...sort of. Here's the details:
At first, I plugged my arch USB drive into my main desktop, but I got this error when I tried to chroot:
$this->bbcode_second_pass_code('', '
failed to run command `/bin/bash': Exec format error
')
I guess it's because I'm trying to chroot into an ARM system via an amd64 host, so I booted up my outdate but working (pre-systemd) tonido arch image via a USB hub, then I plugged in the new (non-working) USB drive along side it and chrooted in that way.
I ran "systemctl enable sshd.socket" as nicux recommended, and I got this output:
$this->bbcode_second_pass_code('', 'ln -s '/usr/lib/systemd/system/sshd.socket' '/etc/systemd/system/sockets.target.wants/sshd.socket'')
Then I tried booting it and I got this error when I tried to SSH:
$this->bbcode_second_pass_code('', 'ssh_exchange_identification: Connection closed by remote host')
Obviously enough it's because I hadn't run "ssh-keygen -A". Once I did that, I was able to successfully SSH in with the default root/root username/pass!
In summary, the whole process was:
$this->bbcode_second_pass_code('', '
#this first line may vary for you. sda is my working (pre-systemd) arch drive, sdb is the partition I'm working on with a fresh arch image.
mount /dev/sdb1 /mnt/usb
cd /mnt/usb
mount -t proc proc proc/
mount -t sysfs sys sys/
mount -o bind /dev dev/
mount -t devpts pts dev/pts/
chroot /mnt/usb
systemctl enable sshd.socket
ssh-keygen -A
')
However, the first thing I tried was removing the two extra lines in /etc/network.d/wired-eth0 (to see if they were part of the solution or not). vi wouldn't open the file, though (no error message or anything). So I tried "pacman -Syu" and I got this output:
$this->bbcode_second_pass_code('', '
:: Synchronizing package databases...
error: failed to update core (unable to lock database)
error: failed to update extra (unable to lock database)
error: failed to update community (unable to lock database)
error: failed to update alarm (unable to lock database)
error: failed to update aur (unable to lock database)
error: failed to synchronize any databases
error: failed to init transaction (unable to lock database)
error: could not lock database: Read-only file system
')
Following this thread (it's not quite the same, but worth a shot), I plugged the USB drive into my desktop machine and ran fsck. It came up clean, and I'm still getting the Read-only file system error. So I guess I'm stuck again. Great progress, though!