How to free up disk space? which logs/directories to clean?
You can change the default retention policy of oracle log and trace files.  

Source: https://streetkiter.wordpress.com/2011/04/06/do-you-really-need-one-year-old-logs-and-traces-for-your-oracle-database/

Relevant extract:
There are two parameters: SHORTP_POLICY (default 720 hours) and LONGP_POLICY (default 8720 hours). so SHORTP_POLICY is 30 days while LONGP_POLICY is 365 days.

From the commandline run "adrci". In adrci, use the following commands.

adrci&gt; show homes
....(homes are listed)...
adrci&gt; set home diag/....(the location)
adrci&gt; show control
.... (current settings are listed) ....
adrci&gt; set control (SHORTP_POLICY = 168)
adrci&gt; set control (LONGP_POLICY = 720)


And now the traces are dropped after one week (SHORTP) or one month (LONGP).