Saxuality

As I am not Oracle DBA and I am performing maintenance tasks very infrequently I usually get stuck with even simple issues like that archive log is full and database cannot start.

I bit misleading is also error raised during database startup: ORA-03113: end-of-file on communication channel

Real error cause can be found in the alert log:
$ less /u01/app/oracle/diag/rdbms/orcl/orcl/alert/log.xml 

Following steps can help:

1. From sqlplus run command: startup mount;
2. Delete archive logs using RMAN: connect target sys/sys@orcl; and then delete archivelog all;
3. Finally just remount database from sqlplus: shutdown; and startup;