Oracle21cをRPMパッケージでインストールする方法

3.1 Modify the initialization script, note that you need to change it to your own service name and character set, etc.
vim /etc/init.d/oracledb_ORCLCDB-21c 
Change the contents to the following:
export ORACLE_HOME=/opt/oracle/product/21c/dbhome_1
export ORACLE_SID=ORA21C
export TEMPLATE_NAME=General_Purpose.dbc
export CHARSET=ZHS16GBK
export PDB_NAME=ORA21CPDB
export LISTENER_NAME=LISTENER
export NUMBER_OF_PDBS=1
export CREATE_AS_CDB=true
3.2 Since the custom service name has been changed, you need to copy a configuration file.
scp /etc/sysconfig/oracledb_ORCLCDB-21c.conf /etc/sysconfig/oracledb_ORA21C-21c.conf 
3.3 Execute the script for database initialization
/etc/init.d/oracledb_ORCLCDB-21c configure
# Note that this step may take a bit longer and you need to wait for successful execution
# This is where the CentOS8 error occurs, causing subsequent failures. 
3.4 Modify the environment variables to make it possible to log in to the database and set NLS_LANG so that sqlplus can display Chinese information properly.
vim /etc/profile.d/oracle21c.sh
export ORACLE_HOME=/opt/oracle/product/21c/dbhome_1
export PATH=$PATH:/opt/oracle/product/21c/dbhome_1/bin
export ORACLE_SID=ORA21C
export NLS_LANG='SIMPLIFIED CHINESE_CHINA.AL32UTF8'
Save and switch the user and it will take effect.
3.5 Login to the database and change the oracle system administrator password
passwd oracle
su - oracle
sqlplus / as sysdba
alter user system identified by yournewpassword ;
3.6 Note that you need to add a procedure that will automatically open the pdb at boot time
CREATE TRIGGER open_all_pdbs
   AFTER STARTUP ON DATABASE
BEGIN
   EXECUTE IMMEDIATE 'alter pluggable database all open';
END open_all_pdbs;
/

4.1 Modify the configuration file
vim /etc/oratab
# Note that the N is changed to Y
ORA21C:/opt/oracle/product/21c/dbhome_1:Y
4.2 Set the startup script
vim /usr/bin/oracle.sh
# Add the following content
#! /bin/bash
# script For oracle19c.service
/opt/oracle/product/21c/dbhome_1/bin/lsnrctl start
/opt/oracle/product/21c/dbhome_1/bin/dbstart /opt/oracle/product/19c/dbhome_1
4.3 Setting Executable Permissions
chmod 777 /usr/bin/oracle.sh
4.4 Set up a service, and set it to start automatically on boot
vim /etc/systemd/system/oracle21c.service
# Add the following

[Unit]
Description=Oracle21c
After=syslog.target network.target

[Service]
LimitMEMLOCK=infinity
LimitNOFILE=65535
Type=oneshot
RemainAfterExit=yes
User=oracle
Environment="ORACLE_HOME=/opt/oracle/product/21c/dbhome_1"
ExecStart=/usr/bin/oracle.sh

[Install]
WantedBy=multi-user.target

# Set up bootup
systemctl enable oracle21c
4.5 Reboot the machine for verification. The service is ready to use. 

Download a package for rlwrap on my end
rlwrap-0.43-5.el8.x86_64.rpm
Put it on the machine and run
yum localinstall rlwrap-0.43-5.el8.x86_64.rpm

Modify the previous environment variables and add an alias
alias sqlplus='rlwrap sqlplus'
# Note that there should be no spaces before or after the equal sign.