The Oracle user password contains special characters and thus cannot be logged on. solution:

Today I encountered a strange problem:
Using sqlplus on the client allows normal users to log on, but neither system nor sys users can log on, prompting ORA-12154: TNS: unable to resolve the specified connection identifier
SQL> conn system @ webdata
Enter the password:
ERROR:
ORA-12154: TNS: Unable to parse the specified connection identifier
SQL> conn xgplat @ webdata
Enter the password:
Connected.
I thought the client was a 32-bit server. I used sqlplus to log on to the oracle server.
SQL> conn system @ webdata
Enter password:
ERROR:
ORA-12541: TNS: no listener
SQL> conn xgplat @ webdata
Enter password:
Connected.
I asked some people who are confused and confused about the problem. When someone said it was related to the password file, I thought that the password of my system/sys user contains a @ character.
For example, if my password is 123 @ 456, you can use sqlplus to Log On As sqlplus system/123 @ 456 @ webdata, in this way, sqlplus is understood as the connection string of the database after 123. In this way, an error is reported and a prompt is displayed, indicating that the specified connection identifier or no listener cannot be resolved.
After logging on to the server with sqlplus/as sysdba, change the password of sys/system and try again.

When the password of an Oracle Database User contains special characters such as @, the user can directly use the normal password for input. the login fails because oracle resolves the characters After @ into the network service name.
In the following example, the username is: wang and the password is oracle @ 1. The network service name is sun:

Linux platform: 'Wang/"oracle @ 1" '@ sun -- a double quotation mark password, one single quotation mark username + password, that is, 'username/"password"' @ service name
[11: 41: 14oracle @ dvd adump] $ sqlplus wang/oracle @ 1 @ sun
SQL * Plus: Release 11.2.0.1.0 Production on Tue Oct 30 11:41:24 2012
Copyright (c) 1982,200 9, Oracle. All rights reserved.
ERROR:
ORA-12532: TNS: invalid argument
[11: 42: 24oracle @ dvd adump] $ sqlplus 'wang/"oracle @ 1"' @ sun -- password for a double quotation mark extension, and username and password for a single quotation mark extension, that is: 'User name/"password" '@ service name
SQL * Plus: Release 11.2.0.1.0 Production on Tue Oct 30 11:42:25 2012
Copyright (c) 1982,200 9, Oracle. All rights reserved.
Connected:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0-Production
With the OLAP and Data Mining options
Wang @ SUN>

Windows Platform: Wang/"" oracle @ 1 "@ sun -- three double quotation marks for password extension, that is, username/" "password" "@ service name
C: \ Users \ wanglei. ITADMIN> sqlplus wang/oracle @ 1 @ sun
SQL * Plus: Release 11.2.0.1.0 Production on Tuesday October 30 13:20:00 2012
Copyright (c) 1982,201 0, Oracle. All rights reserved.
ERROR:
ORA-12154: TNS: Unable to parse the specified connection identifier
Enter the User Name:
C: \ Users \ wanglei. ITADMIN> sqlplus wang/"" oracle @ 1 "@ sun -- password added with three double quotes, that is, username/" "password" @ service name
SQL * Plus: Release 11.2.0.1.0 Production on Tuesday October 30 13:20:30 2012
Copyright (c) 1982,201 0, Oracle. All rights reserved.
Connect:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0-Production
With the OLAP and Data Mining options