Why doesn't the server boot on Linux Debian?

Question

linux

Hello.
After rebooting the server via ssh with the reboot command, the server no longer starts. You can not connect to it, pings do not go to it.
The hoster has the ability to restart it from the control panel, I tried it, but it did not help.
You can also boot into rescue mode and mount server disks to access information, but I don’t know how to use this, because I don’t know how to use it. I'm not very experienced with Linux.
Please tell me how to start the server.

Answer 1

(device md2): ext4_dx_add_entry: Directory index full!

This is the problem - the inodes overflowed.
You can find folders with a large number of files like this:

find <точка монтирования файловой системы> -type d | ( while read A; do B=`ls -l "$A" | wc -l`; if [ "$B" -gt 999 ] ; then echo $B $A; fi ; done)