Install ncdu, then sudo ncdu -x /var it’ll tell you what is taking up space, then if you tell us, we can help you identify how to minimize it and keep it low.

See what’s using the space. This will list any dirs using >100MiB:

sudo du -h -d 5 -t 100M /var

You can use du -sh to figure out what’s using most of the space. Something along the line of:

sudo -i
du -sh /home /usr /var
du -sh /var/*
du -sh /var/log/*
# etc

If it’s one of your log files (likely), you can run something like tail -n 100 /var/log/[culprit] or tail -F /var/log/[culprit] to see what is being flooded in this log file exactly. Then you can try to fix it.

We can’t really help until you tell us what’s using the space. Could be databases, could be docker, could be logs.

I use… du -xh --max-depth 2 /var/ | sort -h

If you suspect that the issue is journald, you can use the following command to check how much space it is using:

journalctl --disk-usage

Rather than periodically running journalctl --vacuum-size=500 to free up space, you can just limit the journal by adding the following to a new file such as /etc/systemd/journald.conf.d/size.conf:

[Journal]
SystemMaxUse=512M

This will limit the journal from using more than 512MB. That said, if journald is filling up fast, then something is spamming your logs and you could run journalctl -a -f to get a sense of what is being written to your logs.

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If it’s an ssd you should try running fstrim manually.

https://linuxhint.com/fstrim-linux-command/