/etc/hosts file was overwritten by WSL at some point

[ownmaster]

I had a hosts file with different content inside WSL for quite a long period of time (a few months at least, if not a year) and today I saw that it's content has been overwritten by System32\drivers\etc\hosts.
Now /etc/hosts starts with:

# This file is automatically generated by WSL based on the Windows hosts file:
# %WINDIR%\System32\drivers\etc\hosts. Modifications to this file will be overwritten.

I would like to understand:

1. Since I never added those lines manually, it must be added during some system update - if I remove these lines does it really mean, that the file inside WSL will not be overwritten?
2. Does WSL store a backup of this file somewhere, so I can restore it?
3. If I decide to enable automatic file generation, can I force this process somehow without system reboot?

Windows version: 10.0.16299.309

[benhillis]

The ability to disable automatic generation of the /etc/hosts file became available in build 17093 and is coming to stable builds of Windows in the next cumulative update which is due soon:
https://docs.microsoft.com/en-us/windows/wsl/wsl-config#set-wsl-launch-settings

[ownmaster]

@benhillis so, I assume that the answer for 2 other questions is 'no': there is no backup by WSL and user can't trigger file update manually?

[benhillis]

Unfortunately the old /etc/hosts file was not backed up. The generated hosts file will be re-created when a new instance is launched.

[ownmaster]

@benhillis seems that all existing WSL console sessions must be closed before new session can get an updated hosts file.

[benhillis]

@ownmaster - Correct, that is what I mean by a new instance.

[ajit555db]

Add the hosts as follows:

Open the following file in Notepad admin mode:
"C:\Windows\System32\drivers\etc\hosts"

add your hosts this at the end of the file e.g.

192.168.2.30 ubmaster
192.168.2.31 ubworker1
192.168.2.32 ubworker2
192.168.2.33 ubsrv

[CosmicCatnap]

Add the hosts as follows:

Open the following file in Notepad admin mode:
"C:\Windows\System32\drivers\etc\hosts"

add your hosts this at the end of the file e.g.

192.168.2.30 ubmaster
192.168.2.31 ubworker1
192.168.2.32 ubworker2
192.168.2.33 ubsrv

The issue in question is not how to find a workaround, its why WSL thinks it should be responsible for a core linux feature and why it transparently erases changes in a way that is against virtually every use case for WSL I can think of.. You should be given a blank hosts file because this issue was self-inflicted.

[treysis]

Additionally to the windows hosts file, Ubuntu adds some own entries at the end of /etc/hosts. What is the basis for these lines? I want to add ::1 localhost because for some reason Ubuntu's default decided that this would not be good. I disagree. It's the default on many systems, including Debian, Windows, and macOS.