数据库：oracle 19.12
系统：rhel 8.4
问题描述：oracle用户下ORACLE_HOME/network/admin/目录下sqlnet.ora文件存在时，sqlplus / as sysdba连接数据库异常，不存在时sqlplus / as sysdba连接正常
[oracle@dbserver admin]$ mv sqlnet01.ora sqlnet.ora
[oracle@dbserver admin]$ cat sqlnet.ora 
# sqlnet.ora Network Configuration File: /u01/app/oracle/product/19.12.0/db_1/network/admin/sqlnet.ora
# Generated by Oracle configuration tools.

# This file is actually generated by netca. But if customers choose to 
# install "Software Only", this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES,EZCONNECT) 
[oracle@dbserver ~]$ sqlplus / as sysdba

SQL*Plus: Release 19.0.0.0.0 - Production on Sat Jul 23 15:52:11 2022
Version 19.12.0.0.0

Copyright (c) 1982, 2021, Oracle.  All rights reserved.

ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name: 
ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name: 
ERROR:
ORA-01017: invalid username/password; logon denied


SP2-0157: unable to CONNECT to ORACLE after 3 attempts, exiting SQL*Plus
[oracle@dbserver admin]$ mv sqlnet.ora sqlnet01.ora
[oracle@dbserver ~]$ sqlplus / as sysdba

SQL*Plus: Release 19.0.0.0.0 - Production on Sat Jul 23 15:52:45 2022
Version 19.12.0.0.0

Copyright (c) 1982, 2021, Oracle.  All rights reserved.


Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.12.0.0.0

其实asm单实例环境在grid用户下ORACLE_HOME/network/admin目录下也有一个sqlnet.ora
[grid@dbserver grid]$ cd network/admin
[grid@dbserver admin]$ ll
total 16
-rw-r-----. 1 grid oinstall  558 Sep 11  2021 listener.ora
drwxr-xr-x. 2 grid oinstall   64 Apr 17  2019 samples
-rw-r--r--. 1 grid oinstall 1536 Feb 14  2018 shrept.lst
-rw-r-----. 1 grid oinstall  177 Sep 11  2021 sqlnet.ora
-rw-r--r--. 1 grid oinstall  402 Jul  4 10:15 tnsnames.ora
oracle用户下的sqlnet.ora是笔者后面添加用作测试，将其删掉后，就可以通过操作系统认证的方式连接数据库.
[oracle@dbserver admin]$ ll
total 12
drwxr-xr-x. 2 oracle oinstall   64 Jul  9 09:54 samples
-rw-r--r--. 1 oracle oinstall 1536 Feb 14  2018 shrept.lst
-rw-r--r--. 1 oracle oinstall  449 Jul 23 15:39 sqlnet.ora
-rw-r-----. 1 oracle oinstall 1274 Jul 21 17:34 tnsnames.ora