If you’ve had your phone for a while now and haven’t done a clean install or re-flashed the OS recently, there’s a good chance you can reclaim a significant amount of disk space by hoovering up the journal logs.
From the terminal you can see how much disk space the journal logs are currently occupying with…
sudo journalctl --disk-usage
Having just checked with a friends phone who re-flashed Amber approx 5 months ago, they had around 4GB worth of journal log files.
Before you can hoover them, you need to rotate the logs to archive them…
sudo journalctl --flush --rotate
If you need/want to have a clear out, you can clear them by time, file count or size.
To clear out by time, for example to keep the last 3 days of logs and clear everything else…
sudo journalctl --vacuum-time=3d
To clear out by files count, for example to keep the last 5 log files and clear everything else…
sudo journalctl --vacuum-files=5
To clear out by size, for example to keep the last 200 MB of logs and clear out everything else…
sudo journalctl --vacuum-size=200M
You should be able to combine the rotate with the vacuum, for example to flush and hoover everything except the logs of the last week…
sudo journalctl --flush --rotate --vacuum-time=1w
For me, I only check the logs for reproducible problems, so I have disabled journal logging for day to day and only enable it when I need/want to check for info/detail of a problem.