One of the PhoneLab participants accidentally forgot the PIN code for his phone, thus can not access the phone at all. There are tremendous tutorials online on how to solve this. This is what I tested and worked.
Since PhoneLab devices are flashed with Clockworkmod recovery, I reboot the
phone (Nexus 5) into recovery mode, mount /system and /data partitions, adb
shell into the phone, and delete these two files: /data/system/password.key
and /data/system/gesture.key. Then the problem was fixed: no lock screen after
powering on the phone.
These are two methods that I tried yet failed. Both have something to do
with the settings.db file.
adb shell
cd /data/data/com.android.providers.settings/databases
sqlite3 settings.db
update system set value=0 where name='lock_pattern_autolock';
update system set value=0 where name='lockscreen.lockedoutpermanently';
.quit
And this one (from xda-developers forum):
adb shell
sqlite3 /data/data/com.android.providers.settings/databases/settings.db
sqlite> update secure set value=65536 where name='lockscreen.password_type';
sqlite> .exit
# exit
adb reboot