Difference between server-id and server_id in MySQL

Question

Running show variables like 'server%' shows server_id as variable name.

But in my.cnf , there's an entry for server-id (although commented out)

Is there any differece between the them?

Answer 1

They are same but as it is stated in this post , if your server-id is not changed by setting my.cfg you can try setting it by underscore

[mysqld]
server_id = 2

Answer 2

MySQL

4.2.9 Using Options to Set Program Variables :

...

If you like, underscores in a variable name can be specified as dashes. The following option groups are equivalent. Both set the size of the server's key buffer to 512MB:

 [mysqld] key_buffer_size=512M [mysqld] key-buffer-size=512M 

...

MariaDB

Server System Variables and mysqld Options :

...

By convention, server variables have usually been specified with an underscore in the configuration files, and a dash on the command line. You can however specify underscores as dashes - they are interchangeable.

...

Test MySQL

File: my.cnf

[mysqld]
. 
.
.
server_id=987
.
.
.

Command-Line:

$ mysql --execute="SELECT VERSION(), @@server_id"
+-----------+-------------+
| VERSION() | @@server_id |
+-----------+-------------+
| 8.0.13    |         987 |
+-----------+-------------+

File: my.cnf

[mysqld]
.
.
.
server-id=321
.
.
.

Command-Line:

$ sudo systemctl restart mysql

$ mysql --execute="SELECT VERSION(), @@server_id"
+-----------+-------------+
| VERSION() | @@server_id |
+-----------+-------------+
| 8.0.13    |         321 |
+-----------+-------------+