cant boot ubuntu server 18.04, ram exhausted?

Question

so i have ubuntu server 18.04, when i try to boot, alot of "depends" fail to start thus i cant boot the server

going to recovery mode i saw one line says memory exhausted, in recovery mode i use free -m and top i see really my memory is stuck at 7.8GB

top output:

KiB Mem : 8040724 total, 135060 free, 7873212 used, 32452 buff/cache

last thing i was doing is importing something to PostgreSQL, and it was stuck at around this much, even after finishing the import, so i restarted and never made it back

btw tried

#sync; echo 1 > /proc/sys/vm/drop_caches
#sync; echo 2 > /proc/sys/vm/drop_caches
#sync; echo 3 > /proc/sys/vm/drop_caches

still same problem

Answer 1

well, i didnt figure out what i did wrong, so i reinstalled the server. and while doing the steps again i noticed where i did go wrong. i was 'following' the steps of this guide: How to Set Up OpenStreetMap Tile Server on Ubuntu 18.04

at one step i should edit /etc/sysctl.conf

sudo nano /etc/sysctl.conf

and add certain value (depending on my setup) to vm.nr_hugepages, for guide it was:

vm.nr_hugepages = 7950

They use 7950 because they have a lot of virtual memory?. so this value is fetal for my setup!