Re: Automatically populate resolv.conf when new DNS is acquired

2018-06-27 Thread Brian Inglis 
On 2018-06-27 03:31, john doe wrote:
> Good morning  Brian, bottom posting.
> By Windows Admin you mean "Windows Admin Center"?

Line wrapped - Windows Admin Tools - on W10 - or search for event (log) viewer

> I'm using Cygwin on a laptop (win 7 pro) and sadly, if I'm not mistaking,
> "Windows Admin" is not available on non-server platform.

May be Administrative Tools on W7

> If I can't find a way to determine when my DNS changes I can clearly emulate
> an hourly cron job by using "task scheduler".

If you're using DHCP it could potentially change when your lease expires,
sometimes a couple of days, (depends on your router settings or ISP: my external
IP changes every few months, internal and DNS never) or if on WiFi, when you
connect to a new AP.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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Re: Automatically populate resolv.conf when new DNS is acquired

2018-06-27 Thread john doe 

Good morning  Brian, bottom posting.

On 6/26/2018 4:18 PM, Brian Inglis wrote:

On 2018-06-26 04:33, john doe wrote:

In gnupg2 the use of dirmngr utility is required to interact with a keyserver.
Dirmngr requires that '/etc/resolv.conf' be populated with my name servers.
That means that everytime the dns changes (new network ...) I need to manually
edit that file.
How can I let Cygwin update that file whenever the DNS is changed?


Attached an awk script to generate resolv.conf from Windows ipconfig /all
output, run from .cygwin_profile (sourced under Cygwin from login .bash_profile)
using the stanza below: it only replaces an existing writable /etc/resolv.conf
when the content changes - touch, chown, chmod /etc/resolv.conf to enable.

# update /etc/resolv.conf if changed
c=/etc/resolv.conf
test -w $c  && \
i=$(/usr/bin/which -- ipconfig) && \
r=$(/usr/bin/which -- resolv.awk)   && \
t=$(/bin/mktemp -t -- resolv.conf.$$.)  && \
if $i /all | $r  >  $t; then
 /usr/bin/cmp -s -- $t $c   || \
 /bin/cp -fv -- $t $c
 /bin/rm -f -- $t
fi

unset c i r t

This could be used in a bash script run from a Windows scheduled task when a
relevant DHCP event occurs: you can find DHCP events by checking Windows Admin
Tools/Event Viewer/Window Logs/System/Filter Current Log/Event
Sources/Dhcp-Client,DHCPv6-Client, or a similar PowerShell script.



Thanks for the awk script and the explanation on how to use it! :)

By Windows Admin you mean "Windows Admin Center"?
I'm using Cygwin on a laptop (win 7 pro) and sadly, if I'm not 
mistaking, "Windows Admin" is not available on non-server platform.


If I can't find a way to determine when my DNS changes I can clearly 
emulate an hourly cron job by using "task scheduler".


Many thanks for the task scheduler hint and for your help.

--
John Doe

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Re: Automatically populate resolv.conf when new DNS is acquired

2018-06-26 Thread Brian Inglis 
On 2018-06-26 04:33, john doe wrote:
> In gnupg2 the use of dirmngr utility is required to interact with a keyserver.
> Dirmngr requires that '/etc/resolv.conf' be populated with my name servers.
> That means that everytime the dns changes (new network ...) I need to manually
> edit that file.
> How can I let Cygwin update that file whenever the DNS is changed?

Attached an awk script to generate resolv.conf from Windows ipconfig /all
output, run from .cygwin_profile (sourced under Cygwin from login .bash_profile)
using the stanza below: it only replaces an existing writable /etc/resolv.conf
when the content changes - touch, chown, chmod /etc/resolv.conf to enable.

# update /etc/resolv.conf if changed
c=/etc/resolv.conf
test -w $c  && \
i=$(/usr/bin/which -- ipconfig) && \
r=$(/usr/bin/which -- resolv.awk)   && \
t=$(/bin/mktemp -t -- resolv.conf.$$.)  && \
if $i /all | $r  >  $t; then
/usr/bin/cmp -s -- $t $c|| \
/bin/cp -fv -- $t $c
/bin/rm -f  -- $t
fi

unset c i r t

This could be used in a bash script run from a Windows scheduled task when a
relevant DHCP event occurs: you can find DHCP events by checking Windows Admin
Tools/Event Viewer/Window Logs/System/Filter Current Log/Event
Sources/Dhcp-Client,DHCPv6-Client, or a similar PowerShell script.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
#!/usr/bin/awk -f
# resolv.awk - create Windows resolv.conf from ipconfig /all output

{ sub( /\r/, "", $NF) } # trim \r

# collect DNS domain suffixes
/D[Nn][Ss]\sSuffix[^:]*:\s\S/   { domain[$NF] = $NF }

# collect DNS search suffixes
/Search\sList[^:]*:\s\S/{ search[$NF] = $NF }

# collect DNS server IP addresses
/DNS\sServers[^:]*:\s\S/{ dns = 1 } # enable

dns && $NF ~ /^[0-9.]+$/{ nameserver[++ns] = $NF }  # collect

dns && $NF !~ /^[0-9.]+$/   { dns = 0 } # disable

# output unique resolv.conf entries
END {
for (n = 1; n <= ns; ++n)   { print "nameserver", nameserver[n] }

for (d in domain)   { print "domain", domain[d] }

p = "search"

for (s in search)   {
printf "%s %s", p, search[s]
p = ""
}

if (!p) { print p }
}


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