why the oracle with ORA-01034 and ORA-27101 startup container

[jiasha]

while container started, i go in this container and i working sqlplus,but there wasn`t some infomation of connection.
unreal@ubuntu:~$ sudo docker exec -it 22daa352f0b0 /bin/bash
[sudo] password for unreal:
root@22daa352f0b0:/# su oracle
oracle@22daa352f0b0:/$ $ORACLE_HOME/bin/sqlplus / as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Tue Mar 12 10:59:33 2019

Copyright (c) 1982, 2014, Oracle. All rights reserved.

Connected to an idle instance.

SQL>
---------------------------------------end------------------
start logs
unreal@ubuntu:~$ sudo docker logs 22daa352f0b0
found files in /u01/app/oracle/oradata Using them instead of initial database
ORA-00821: Specified value of sga_target 768M is too small, needs to be at least 1108M
Starting web management console
BEGIN DBMS_XDB.sethttpport(8080); END;

ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
Session ID: 0 Serial number: 0

[IMPORT] Not a first start, SKIPPING Import from Volume '/docker-entrypoint-initdb.d'
[IMPORT] If you want to enable import at any state - add 'IMPORT_FROM_VOLUME=true' variable

Database ready to use. Enjoy! ;)