WSL2: resolver ignores LOCALDOMAIN env variable

[joslinpr]

Windows Build Number

Microsoft Windows [Version 10.0.18363.1621]

WSL Version

• WSL 2
• WSL 1

Kernel Version

Linux version 5.10.43.3-microsoft-standard-WSL2 (oe-user@oe-host) (x86_64-msft-linux-gcc (GCC) 9.3.0, GNU ld (GNU Binutils) 2.34.0.20200220) #1 SMP Wed Jun 16 23:47:55 UTC 2021

Distro Version

CentOS Linux release 7.9.2009 (Core)

Other Software

Not applicable.

Repro Steps

# cat /etc/resolv.conf
# This file was automatically generated by WSL. To stop automatic generation of this file, add the following entry to /etc/wsl.conf:
# [network]
# generateResolvConf = false
nameserver <Windows IP>

# nslookup SERVER
Server:     <Windows IP>
Address:    <Windows IP>

# export LOCALDOMAIN="domainA.example.com domainB.example.com domainC.example.com"
# nslookup SERVER
Server:     <Windows IP>
Address:    <Windows IP>
** server can't find SERVER: NXDOMAIN

# sudo bash -c "cat /etc/resolv.tmpl >> /etc/resolv.conf"
# cat /etc/resolv.conf
# This file was automatically generated by WSL. To stop automatic generation of this file, add the following entry to /etc/wsl.conf:
# [network]
# generateResolvConf = false
nameserver <Windows IP>
search example.com domainA.example.com domainB.example.com domainC.example.com

# nslookup SERVER
Server:     <Windows IP>
Address:    <Windows IP>

Non-authoritative answer:
SERVER.domainA.example.com  canonical name = SERVER.domainB.example.com.
Name:   SERVER.domainB.example.com
Address: <redacted> #  <--- correct address returned.

Expected Behavior

resolver seems to be ignoring environment variables.

On RHEL 7.9, setting LOCALDOMAIN overrides any search directive in /etc/resolv.conf. This is documented in the man pages (man resolv.conf):

The search keyword of a system's resolv.conf file can be overridden on a per-process basis by setting the environment variable LOCALDOMAIN to a space-separated list of search domains.

# cat /etc/resolv.conf
search          domainA.example.com example.com
nameserver      <redacted>
nameserver      <redacted>

# LOCALDOMAIN="domainB.example.com example.com" nslookup SERVER
Server:         <redacted>
Address:        <redacted>

Non-authoritative answer:
SERVER.domainA.example.com   canonical name = SERVER.domainB.example.com.
Name:   SERVER.domainB.example.com
Address: <redacted>

• In my organization, "hostname" is set to shortname, not a fully qualified domain name.
• It appears /etc/resolv.conf is recreated each time a wsl session starts? A file with a "search" directive is overwritten. The address added to resolv.conf is the correct IP for my Windows laptop.
• I cannot use generateResolvConf = false because my IP address changes.

Actual Behavior

resolver fails unless there is a domain or search directive containing the proper domain. Adding a LOCALDOMAIN environment variable does not fix the problem.

Diagnostic Logs

I have created a GIST with the output of
strace nslookup host.example.com
and
LOCALDOMAIN="domainB.example.com" strace nslookup host.example.com.

To my casual inspection they look identical.

[benhillis]

For WSL2 the DNS resolver runs on the host, so the Linux environment variables will not be respected.

[joslinpr]

Thanks for responding. So this will remain "working as intended"?

Guess I'll hack up a file watcher or cron job to camp on /etc/resolv.conf.

[mat-m]

Thanks for responding. So this will remain "working as intended"?

Guess I'll hack up a file watcher or cron job to camp on /etc/resolv.conf.

You can chattr +i as suggested in #5420

[microsoft-github-policy-service]

This issue has been automatically closed since it has not had any activity for the past year. If you're still experiencing this issue please re-file this as a new issue or feature request.

Thank you!