Oracle. Error code ORA-12154 and Oracle client-free Setup

. Error code ORA-12154
I believe that as the Oracle database developers do not encounter "Ora-12154:tns: Unable to resolve the specified connection identifier", today I also encountered a similar situation, my solution to the summary, I hope to be able to meet the same problems of friends to provide help.
Problem Scenario Description:
Server-side version: Oracle 10.2.0.10
Client version: Oracle 10.2.0.10
Client Development tools: PL/SQL Developer
Through the client to connect to the server, the main file is configured by the client's Tnsnames.ora, on the basis of the original file added:
Sid alias =
(DESCRIPTION =
(Address_list =
(ADDRESS = (PROTOCOL = TCP) (HOST = server_ip) (PORT = 1521))
)
(Connect_data =
(SID = sid_name)
)
)
Cases:
dev_db =
(DESCRIPTION =
(Address_list =
(ADDRESS = (PROTOCOL = TCP) (HOST = 172.168.10.5) (PORT = 1521))
)
(Connect_data =
(SID = ora10)
)
)
When connecting dev_db via PL/SQL developer, the "Ora-12154:tns: Unable to resolve the specified connection identifier" is reported. (This problem has been encountered before, but the solution is not the same, because the specific problem is not the same.) ）

I'll tell you some of the solutions I know:
1. First check whether the server-side monitoring service is turned on, if it is not open, start its monitoring
Client: tnsping <tns_name>
Under Server Linux:
#>lsnrctl Status View monitoring status
#>lsnrctl Start Monitoring
2. Try the SQL plus connection, if the SQL plus connection succeeds, it means that your Tnsnames.ora content is wrong
My problem is in the alias dev_db in front of a space, this can be through a text editor (edit Plus,ue, etc.) to see if there are spaces, as long as there are spaces that is certainly not, and if the content is in the middle of the file, it will cause all the corresponding connection alias in the file is unsuccessful , if it is on the last side only its own connection alias is not successful, the other connection alias is still able to connect successfully. (Note: My Tnsnames.ora is configured with multiple DB instance connections, all with multiple connection aliases.) ）
Such as:
Space dev_db =
(DESCRIPTION =
(Address_list =
(ADDRESS = (PROTOCOL = TCP) (HOST = 172.168.10.5) (PORT = 1521))
)
(Connect_data =
(SID = ora10)
)
)
3. If you make sure that your Tnsnames.ora content is not wrong, then please delete all the files in the%oracle_home%\product\10.2.0\db_1\network\admin directory, then reconnect, you can generally solve the problem.
Note: The file in that directory is generated dynamically when you establish a connection, do not be afraid to delete the problem
4. Enter the main interface of the Plsql developer, select Cancel on the login screen without logging into the main interface, then select Menu Tools (Tools)-preferences (preferences), in the Settings window, select Oracle-connection (Connect), In the corresponding Settings window, locate the Oracle Home (Oracle home directory), select the version of the client that you installed locally, save the settings, and then restart Plsql Developer, then you can log in normally.

2: Client Oracle environment variable configuration
Configure Oracle_home=d:\programfiles\oracle-Set the Oracle installation path
Configure Tns_admin=d:\programfiles\oracle
Configure Nls_lang=simplified Chinese_china. ZHS16GBK set to Chinese character set
Modify path, increase;%O Racle_home% Content

Oracle. Error code ORA-12154 and Oracle client-free Setup