How can I free up space to log into Oracle using sqlplus as sysdba? I don't know what I may eliminate. The current directory appears to be full when I run the command df -k to check the amount of free space there.
You can do following things to free the space
1. Look at the DIAG DESTINATION, such as /u01/app/oracle/diag/, if your Oracle installation is on your root drive. If there are a lot of outdated trace files there, you can erase them without risk using adrci.
2. CHECK for RMAN Backup log, sometime this is also allocating the space.
3. Check for dba_directories view for the datapump location and delete the old dumps
4. Check CRONTAB -l for schedule scripts and their log file and delete the obsolete.
5. If OEM is configure, check for the logs and delete it as OEM generates more logs and allocate more space.
6. Some time Archives are not being cleared due to RMAN is failing. Check for the RMAN backups and Run the full backup and then take the archive backup and clear the archived backup from RMAN.