"/dev/vda1" is 100% full

I have a problem with Ubuntu 16.04.2, that the server is full. This is because of the "vda1" that uses 100% of the disk:

Filesystem Size Used Avail Use% Mounted on
udev 991M 0 991M 0% /dev
tmpfs 201M 5.7M 195M 3% /run
/dev/vda1 9.7G 9.7G 0 100% /

I have checked for log files, but none of the files in /var/log is nearly big enough.

Searching for big files with find / -type f -size +100M -exec ls -lh {} \; gives a couple of big files, but nearly big enough that it should be full:

-r-------- 1 root root 128T Aug 14 10:18 /proc/kcore
find: ‘/proc/5938/task/5938/fdinfo/6’: No such file or directory
find: ‘/proc/5938/fdinfo/5’: No such file or directory
-rw-r----- 1 mysql mysql 512M Aug 14 10:17 /var/lib/mysql/ib_logfile0
-rw-r----- 1 mysql mysql 512M Aug 14 09:31 /var/lib/mysql/ib_logfile1
-rw------- 1 root root 204M Aug 14 10:16 /var/lib/fail2ban/fail2ban.sqlite3

I have tried commands like sudo apt autoremove to remove old packages, but the command cannot be run because of no space left on device. The same goes for ncdu which I cannot install because of full space.

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