How to set sharepoint site to read only

How to set sharepoint site to read only?

 set sharepoint site to read only is required while doing the Migration from On-premise to online.

The steps are same for all: 2010, 2013 and 2016.  

We can achieve this in  3 options as shown below.

Through Central Administration:

1. Go to Central Admin > Application Management > Configure quotas and locks.
2. Select the site collection which should be read-only and select the “Read-Only” radio button. Click OK.
3. Now, browse the site collection and we can see a message on the top saying, “This site is read-only at the farm administrator’s request”.
4. when the site is set to read-only,user can only view the document or download a copy of it.
   

Through Database:

1. Select the content database and go to its Properties.
2. Click on Options menu from the left-hand side of the window and under the "State" section, set “Database Read-Only” to “True”, as shown in the image below.
3. Now, the content database is in read-only mode.

Through PowerShell:

I hope the above information will help you to resolve the issue, in case of any queries/questions regarding the above mentioned information then please let me know. I would be more than happy to help you as well as resolves your issues, Thank you.