[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

It's postfix@$INSTANCE.  If you don't have multi-instance setup, the
default instance is "-", so you would look for postfix@-, not postfix@.
This is discussed in README.Debian.  You should probably file a new bug
for this problem if you don't get it figured out.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Mark Sapiro]

This bug is back in Ubuntu 20.04 postfix/focal-updates,now
3.4.13-0ubuntu1.2

I'm not certain of my analysis, but I see two services

postfix.service -
[Unit]
Description=Postfix Mail Transport Agent
Conflicts=sendmail.service exim4.service
ConditionPathExists=/etc/postfix/main.cf

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/true
ExecReload=/bin/true

[Install]
WantedBy=multi-user.target
-
and
postfix@.service 
[Unit]
Description=Postfix Mail Transport Agent (instance %i)
Documentation=man:postfix(1)
PartOf=postfix.service
Before=postfix.service
ReloadPropagatedFrom=postfix.service
After=network-online.target nss-lookup.target
Wants=network-online.target

[Service]
Type=forking
GuessMainPID=no
ExecStartPre=/usr/lib/postfix/configure-instance.sh %i
ExecStart=/usr/sbin/postmulti -i %i -p start
ExecStop=/usr/sbin/postmulti -i %i -p stop
ExecReload=/usr/sbin/postmulti -i %i -p reload

[Install]
WantedBy=multi-user.target
-
It appears the intent of postfix@.service is to delay starting postfix.service 
until after networking is up, but it seems that systemd doesn't accept 
postfix@.service as a valid service

$ sudo systemctl status postfix@.service 
Failed to get properties: Unit name postfix@.service is neither a valid 
invocation ID nor unit name.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Launchpad Bug Tracker]

This bug was fixed in the package postfix - 3.1.4-4ubuntu1

---
postfix (3.1.4-4ubuntu1) zesty; urgency=medium

  * Use correct service dependencies in postfix@.service, to avoid racing
systemd-resolved at boot.  LP: #1519331.

 -- Steve Langasek   Sat, 03 Jun 2017
00:35:57 -0700

** Changed in: postfix (Ubuntu Zesty)
   Status: Fix Committed => Fix Released

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Łukasz Zemczak]

The reason for it not being released for zesty before was that it seemed
to have 3 undefined autopkgtest failures for sbuild. After looking into
those now, it seems that the sbuild autopkgtests seem to be constantly
failing for those 3 archs for all packages - so, (most likely) unrelated
to the postfix upload. I would say that's enough for me to get it
released.

On it now.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Aaron Peromsik]

Anything in particular holding the release of this fix for Zesty?

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Launchpad Bug Tracker]

This bug was fixed in the package postfix - 3.1.0-5ubuntu1

---
postfix (3.1.0-5ubuntu1) yakkety; urgency=medium

  * Use correct service dependencies in postfix@.service, to avoid racing
systemd-resolved at boot.  LP: #1519331.

 -- Steve Langasek   Sat, 03 Jun 2017
13:00:35 -0700

** Changed in: postfix (Ubuntu Yakkety)
   Status: Fix Committed => Fix Released

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

Test case confirmed also on yakkety.

** Tags removed: verification-needed-yakkety
** Tags added: verification-done-yakkety

** Tags removed: verification-needed

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

Ran through the full test case on zesty and confirmed that this works as
expected.

** Tags removed: verification-needed-zesty
** Tags added: verification-done-zesty

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Christophe Lyon]

I've installed the proposed the package (on zesty), removed my
workaround in /etc/rc.local, rebooted and it seems to work. Thanks!

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[pdecat]

Proposed package installed on zesty, workaround removed
(/etc/systemd/system/postfix@-.service.d/override.conf) and rebooted.


So far so good :)

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Andy Whitcroft]

Hello Erik, or anyone else affected,

Accepted postfix into zesty-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/postfix/3.1.4-4ubuntu1
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-zesty to verification-done-zesty. If it does not fix
the bug for you, please add a comment stating that, and change the tag
to verification-failed-zesty. In either case, details of your testing
will help us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: postfix (Ubuntu Zesty)
   Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-zesty

** Changed in: postfix (Ubuntu Yakkety)
   Status: In Progress => Fix Committed

** Tags added: verification-needed-yakkety

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

** Changed in: postfix (Ubuntu Yakkety)
   Status: Triaged => In Progress

** Changed in: postfix (Ubuntu Zesty)
   Status: Triaged => In Progress

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

** Description changed:

- Every now and then postfix installed on my laptop stops delivering
- mails. I detect this problem after wandering about no answers to my
- emails, or by checking the current mail queue, which should be empty
- when I am at the office.
+ [SRU Justification]
+ Race condition between resolvconf and postfix on startup leaves postfix with 
a different DNS server configuration in its chroot than is used on the host 
system, which may cause it to experience DNS resolution errors.
+ 
+ [Test case]
+ 1. Install postfix on a machine or container (not chroot) in the default 
configuration.
+ 2. Run 'sudo mkdir -p /etc/systemd/system/systemd-resolved.service.d ; echo 
-e '[Service]\nExecStartPre=/bin/sleep 20' | sudo tee 
/etc/systemd/system/systemd-resolved.service.d/lp1519331.conf'
+ 3. Reboot
+ 4. Confirm that /etc/resolv.conf and /var/spool/postfix/etc/resolv.conf 
differ.
+ 5. Install postfix from -proposed
+ 6. Reboot
+ 7. Confirm that /etc/resolv.conf and /var/spool/postfix/etc/resolv.conf match.
+ 8 Run 'sudo rm -f 
/etc/systemd/system/systemd-resolved.service.d/lp1519331.conf && sudo rmdir -p 
/etc/systemd/system/systemd-resolved.service.d'
+ 
+ [Regression potential]
+ Because we are changing the order of service initialization at boot, if there 
are other packages which have undeclared dependencies on postfix (or 
generically, on a running SMTP server), these services may now fail a race with 
postfix startup where they succeeded before.  This is highly unlikely, as a 
hard dependency on an SMTP service is unusual.
+ 
+ Because the postfix service will now depend on network-online.target, if
+ the system fails to reach this target postfix will not start, which
+ would be a serious regression.  Analysis shows that network-
+ online.target should always be reached at boot, regardless of whether
+ using ifupdown, network-manager, or networkd, and the only difference is
+ that postfix startup will be delayed a short while until the network is
+ fully configured.
+ 
+ 
+ [Original report]
+ Every now and then postfix installed on my laptop stops delivering mails. I 
detect this problem after wandering about no answers to my emails, or by 
checking the current mail queue, which should be empty when I am at the office.
  
  I use postfix to deliver all sent mail to the company SMTP server. The
  local postfix does not receive outside mail.
  
  The mail queue shows errors of the type:
  
  (Host or domain name not found. Name service error for name=
  type=: Host not found, try again)
  
  When I manually check host name resolution, it works fine. It seems,
  postfix either does not retry name resolution, or somehow name
  resolution fails for postfix, but not other programs. Network
  connectivity is fine when this problem occurs (I read my mail via IMAP
  w/o local message body cache from the same server used as smart host,
  use SSH to other hosts, and surf the web -- I never noticed network
  problems when the postfix mail delivery did not work).
  
  To remedy the situation I can just restart postfix and flush the mail
  queue. But I need to detect the problem, and postfix should™ recover on
  its own.
  
  I am using IPv6 privacy extensions (Ubuntu default) in a dual stack IPv4
  and IPv6 network. Both local (company) and remote servers are accessible
  via IPv6, thus I am actively using IPv6 for many connections. I have no
  idea if this is related to the problem, but the error shows a failure to
  resolve a quad A record.
  
  Mandatory information:
  1)
  $ lsb_release -rd
  Description:  Ubuntu 14.04.3 LTS
  Release:  14.04
  
  2)
  $ apt-cache policy postfix
  postfix:
-   Installed: 2.11.0-1ubuntu1
-   Candidate: 2.11.0-1ubuntu1
-   Version table:
-  *** 2.11.0-1ubuntu1 0
- 500 http://ftp.uni-kl.de/pub/linux/ubuntu/ trusty-updates/main amd64 
Packages
- 100 /var/lib/dpkg/status
-  2.11.0-1 0
- 500 http://ftp.uni-kl.de/pub/linux/ubuntu/ trusty/main amd64 Packages
+   Installed: 2.11.0-1ubuntu1
+   Candidate: 2.11.0-1ubuntu1
+   Version table:
+  *** 2.11.0-1ubuntu1 0
+ 500 http://ftp.uni-kl.de/pub/linux/ubuntu/ trusty-updates/main amd64 
Packages
+ 100 /var/lib/dpkg/status
+  2.11.0-1 0
+ 500 http://ftp.uni-kl.de/pub/linux/ubuntu/ trusty/main amd64 Packages
  
  3)
  I expected postfix to deliver the queued mail. If there was a (temporary, 
perhaps very short) network problem, postfix should recover automatically after 
the problem was resolved.
  
  4)
  Postfix stopped delivering mails.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Bug Watch Updater]

** Changed in: postfix (Debian)
   Status: Unknown => Fix Released

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

Marking this high; racing /etc/resolv.conf setup at boot is not just a
desktop issue.

** Changed in: postfix (Ubuntu)
   Status: Confirmed => Fix Released

** Bug watch added: Debian Bug tracker #854475
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=854475

** Also affects: postfix (Debian) via
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=854475
   Importance: Unknown
   Status: Unknown

** Also affects: postfix (Ubuntu Zesty)
   Importance: Undecided
   Status: New

** Also affects: postfix (Ubuntu Yakkety)
   Importance: Undecided
   Status: New

** Changed in: postfix (Ubuntu Yakkety)
   Importance: Undecided => High

** Changed in: postfix (Ubuntu Zesty)
   Importance: Undecided => High

** Changed in: postfix (Ubuntu Yakkety)
 Assignee: (unassigned) => Steve Langasek (vorlon)

** Changed in: postfix (Ubuntu Zesty)
 Assignee: (unassigned) => Steve Langasek (vorlon)

** Changed in: postfix (Ubuntu Yakkety)
   Status: New => Triaged

** Changed in: postfix (Ubuntu Zesty)
   Status: New => Triaged

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

Adding the local recursive name server to
/etc/resolvconf/resolv.conf.d/base (see comment #34) solved the problem
of having an unusable /etc/resolv.conf at the time postfix copies it
during boot. Together with restarting postfix whenever /etc/resov.conf
changes solves my problems.

I would be happy to see a solution that works as well as my manual fixes
added to the postfix and resolv.conf packages.

Thanks,
Erik

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

I have just added something to the file
/etc/resolvconf/resolv.conf.d/base to try to have a useful
/etc/resolv.conf all the time:


```
# workaround for broken interactions with Postfix:
# fall back to the local name server 127.0.1.1
nameserver 127.0.1.1
```

Let's see how this plays out...

Thanks,
Erik

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

Hi,

I see two problems to solve to enable using Postfix on laptops with
changing network connectivity:

1. Copy a working /etc/resolve.conf on initial Postfix start-up
2. Adjust Postfix's copy of /etc/resolv.conf in 
/var/spool/postfix/etc/resolv.conf

Part 1 seems to be tackled with waiting for networking to come up. A
static default using 127.0.1.1 as DNS server might work as well, at
least for Ubuntu 14.04 LTS.

Part 2 can be solved similar to my comment #21, i.e. restarting Postfix
whenever the system resolv.conf changes by using the appropriate
infrastructure for this. Just copying the new file to the change root
might suffice and might be nicer.

My use case is well described by by Steve Langasek as "intermittently
online" machine. I want Postfix to store e-mails if there is no network
connectivity, and send them out, when network connectivity is available.

Back in the day this just worked. There was a static /etc/resolv.conf
and Postfix used the system resolv.conf file. Later enhancements made
/etc/resolv.conf dynamic and Postfix moved to a change root with a local
copy of an /etc/resolv.conf snapshot. Those two changes do not work
together correctly.

BTW, the current status on 14.04 LTS is that Postfix often copies
/etc/resolv.conf before this file is created correctly. Disabling and
then enabling the network (e.g. unplug cable, wait for NetworkManager to
notice, plug cable back in) resolves the issue iff a hook in
/etc/resolvconf/update.d/ picks up the change and updates Postfix. I use
the simple, but heavy-weight script described in comment #21 for this.

Thanks,
Erik

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

On Mon, May 15, 2017 at 09:59:22PM -0700, Steve Langasek wrote:
> > - The penalty of pulling in network-online.target is simply that for the
> > local case postfix is started a bit later then necessary during boot.

> There's no reason that this *should* be true for an intermittently-online
> machine.  The network-online.target is specifically defined so that services
> are not started until the network connection is actually up; or put another
> way, if a system is booted and can't get a network connection, those
> services are not started.  We don't just start them at some random point,
> that would defeat the purpose.

So, I just noticed that NetworkManager-wait-online uses --timeout:

ExecStart=/usr/bin/nm-online -s -q --timeout=30

which means this delays services at most 30 seconds at boot.

And you can ignore my blather about this preventing services from running.
Sorry!

(I'm not convinced that having a timeout is actually sensible behavior, but,
well, it's what's implemented.)

-- 
Steve Langasek   Give me a lever long enough and a Free OS
Debian Developer   to set it on, and I can move the world.
Ubuntu Developerhttp://www.debian.org/
slanga...@ubuntu.com vor...@debian.org

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

Hi Scott,

Adding the Debian bug on Cc:.

On Mon, May 15, 2017 at 10:12:41PM -, Scott Kitterman wrote:
> On Monday, May 15, 2017 08:49:42 PM you wrote:
> > On Mon, May 15, 2017 at 06:45:21PM -, Scott Kitterman wrote:
> > > I'm getting close to uploading a fix for this to Debian, so you might wait
> > > for that.

> > It looks like you've implemented this using the network-online.target
> > approach, which as you mentioned might not DTRT for the localhost-only use
> > case.  Did you decide that this is negligible?

> That was the advice I got from the Debian systemd maintainers (that the 
> impact 
> would be negligible).

Ok, the analysis on the Debian bug looks rather shallow to me:

> - The penalty of pulling in network-online.target is simply that for the
> local case postfix is started a bit later then necessary during boot.

There's no reason that this *should* be true for an intermittently-online
machine.  The network-online.target is specifically defined so that services
are not started until the network connection is actually up; or put another
way, if a system is booted and can't get a network connection, those
services are not started.  We don't just start them at some random point,
that would defeat the purpose.

So the case I described is still not handled here - a postfix setup that has
no dependency on the network interface bring-up (for binding), such as the
default config, will nevertheless be blocked from starting until there is a
network, including in cases where this is much more than a mere startup
timing distinction.

Now, you can't have a single unit config that simultaneously meets Russell's
request from the original bug report, to defer startup until a given bind
address is available, and the case I describe above, where you care about
postfix running even when the network is not up.  I would argue that the
case I outlined is more important to get right out of the box, since it
requires no changes to the default postfix config whereas Russell's use case
does.  But it's your decision as maintainer which to support as the default;
I just won't SRU the network-online.target change into any Ubuntu stable
releases because it would introduce a regression.

> > For the case of a server which always has a network connection, this works
> > fine.  For the case of a standalone system with no configured network
> > connection, it probably also works fine.  But for the case of e.g. a laptop
> > that sometimes has network and sometimes doesn't, if the system comes up
> > without network, postfix will not start and you will not have local
> > delivery.  Is this the behavior you expect with your change?

> I tested this and if you're using NetworkManager at least there's some magic 
> that happens which causes systemd to restart postfix once the network is 
> available.  Part of the reason I was having so much trouble replicating 
> problems others were seeing was getting NM to quit 'helping' as the test 
> system I was using also has a desktop installed.

Do you really mean that it restarts postfix when the network is available,
or is it starting postfix for the first time?  The expected behavior is that
postfix doesn't start at all until the network is up.  This is managed via
/lib/systemd/system/NetworkManager-wait-online.service in both Ubuntu and
Debian.

(FWIW in the process of confirming this, I have identified a bug at least in
Ubuntu, related to LP: #1569649, whereby NetworkManager-wait-online is not
enabled on some systems that have been continuously upgraded from Ubuntu
pre-releases.  I'm working on fixing this now.)

> > Ultimately I want to SRU this into affected stable Ubuntu releases, so would
> > want a regression-free change.
> > 
> > I see you are also setting After=nss-lookup.target.  For the bug reported
> > here - which is about DNS resolution specifically - would it not suffice to
> > have postfix declare this After=nss-lookup.target, and for systemd-resolved
> > to be sequenced before it?

> According to the Debian systemd people, the systemd-resolved is superfluous.  
> It's nss-lookup.target that I wanted all along.

Well, in theory yes, but in practice I see nothing - including
systemd-resolved - that's wired up to this target in Debian or Ubuntu.  The
nss-lookup target does nothing:

$ systemctl status nss-lookup.target
● nss-lookup.target - Host and Network Name Lookups
   Loaded: loaded (/lib/systemd/system/nss-lookup.target; static; vendor preset:
   Active: inactive (dead)
 Docs: man:systemd.special(7)
$ journalctl -u nss-lookup.target
-- No entries --
$

Oh, if you happen to also install bind, then you get this target.  But
that's not the common case.

So your current unit deps work *only* because you are also depending on
network-online.target, and resolvconf handling happens before
network-online.  The After=nss-lookup.target is a complete no-op.  I think
we should fix that so that it's *not* a no-op, but that means touching a few
more moving pieces.

Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

On Monday, May 15, 2017 08:49:42 PM you wrote:
> On Mon, May 15, 2017 at 06:45:21PM -, Scott Kitterman wrote:
> > I'm getting close to uploading a fix for this to Debian, so you might wait
> > for that.
> 
> It looks like you've implemented this using the network-online.target
> approach, which as you mentioned might not DTRT for the localhost-only use
> case.  Did you decide that this is negligible?

That was the advice I got from the Debian systemd maintainers (that the impact 
would be negligible).

> For the case of a server which always has a network connection, this works
> fine.  For the case of a standalone system with no configured network
> connection, it probably also works fine.  But for the case of e.g. a laptop
> that sometimes has network and sometimes doesn't, if the system comes up
> without network, postfix will not start and you will not have local
> delivery.  Is this the behavior you expect with your change?

I tested this and if you're using NetworkManager at least there's some magic 
that happens which causes systemd to restart postfix once the network is 
available.  Part of the reason I was having so much trouble replicating 
problems others were seeing was getting NM to quit 'helping' as the test 
system I was using also has a desktop installed.

> Ultimately I want to SRU this into affected stable Ubuntu releases, so would
> want a regression-free change.
> 
> I see you are also setting After=nss-lookup.target.  For the bug reported
> here - which is about DNS resolution specifically - would it not suffice to
> have postfix declare this After=nss-lookup.target, and for systemd-resolved
> to be sequenced before it?

According to the Debian systemd people, the systemd-resolved is superfluous.  
It's nss-lookup.target that I wanted all along.

There's a very helpful (at least for me) discussion in the last few entries in 
the Debian bug.  Reviewing that would be better advice than I have for what's 
safe/not as I cribbed from Michael Biebl's suggestions after just enough 
research to be able to convince myself I wasn't cargo culting.

Scott K

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

On Mon, May 15, 2017 at 06:45:21PM -, Scott Kitterman wrote:
> I'm getting close to uploading a fix for this to Debian, so you might wait
> for that.

It looks like you've implemented this using the network-online.target
approach, which as you mentioned might not DTRT for the localhost-only use
case.  Did you decide that this is negligible?

For the case of a server which always has a network connection, this works
fine.  For the case of a standalone system with no configured network
connection, it probably also works fine.  But for the case of e.g. a laptop
that sometimes has network and sometimes doesn't, if the system comes up
without network, postfix will not start and you will not have local
delivery.  Is this the behavior you expect with your change?

Ultimately I want to SRU this into affected stable Ubuntu releases, so would
want a regression-free change.

I see you are also setting After=nss-lookup.target.  For the bug reported
here - which is about DNS resolution specifically - would it not suffice to
have postfix declare this After=nss-lookup.target, and for systemd-resolved
to be sequenced before it?

-- 
Steve Langasek   Give me a lever long enough and a Free OS
Debian Developer   to set it on, and I can move the world.
Ubuntu Developerhttp://www.debian.org/
slanga...@ubuntu.com vor...@debian.org

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

I'm getting close to uploading a fix for this to Debian, so you might wait for 
that.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Steve Langasek]

I am seeing this issue on Ubuntu 17.04.

/var/spool/postfix/etc/resolv.conf is pointing at 192.168.122.1, which
is the IP of my libvirt bridge - this is a result of dnsmasq interfacing
with resolvconf, so that the host system can resolve local hostnames of
guests on the bridge.

It's fine that 192.168.122.1 is listed (aside from the part where I've
killed the dnsmasq there for unrelated reasons), but this differs from
the host resolv.conf, which points to 127.0.0.53 first.  We should
*always* be pointing to 127.0.0.53 (systemd-resolved) on Ubuntu 16.10
and later.  The fact that we aren't means postfix is racing systemd-
resolved at boot.

I think it should be a sufficient fix for this bug, on 16.10 and later,
to have /lib/systemd/system/postfix.service declare After=systemd-
resolved.service.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[pdecat]

Same issue here on zesty, empty /var/spool/postfix/etc/resolv.conf after
reboot.

Applying solution from #24 works it around:

```
# printf "[Unit]\nAfter=network-online.target\n" | sudo SYSTEMD_EDITOR=tee 
systemctl edit postfix@-.service
```

Current working configuration:

```
# systemctl cat postfix@-.service
# /lib/systemd/system/postfix@.service
[Unit]
Description=Postfix Mail Transport Agent (instance %i)
Documentation=man:postfix(1)
PartOf=postfix.service
ReloadPropagatedFrom=postfix.service

[Service]
Type=forking
GuessMainPID=no
ExecStartPre=/usr/lib/postfix/configure-instance.sh %i
ExecStart=/usr/sbin/postmulti -i %i -p start
ExecStop=/usr/sbin/postmulti -i %i -p stop
ExecReload=/usr/sbin/postmulti -i %i -p reload

[Install]
WantedBy=multi-user.target

# /etc/systemd/system/postfix@-.service.d/override.conf
[Unit]
After=network-online.target
```

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[gil]

Another confirmation that this bug is still present in Zesty, and that
the solution in #24 has worked fine for me so far.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[hambling]

Had the same problem before Zesty and used some of the fixes described
here to have postfix restart through rc.local file after waiting a few
minutes. The bug is still persistent for me after upgrading to Zesty.
What does fix it for me though is adding the "After" line to the Unit:
/lib/systemd/system/postfix@.service

After=network-online.target

Note: it did not work to make this change to the postfix.service unit.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Eugene Crosser]

I experience this on Zesty, on an always-on machine, that however relies
on DHCP for network configuration.

I would argue that this is an upstream bug, or if you want a design
flaw.

It is perfectly normal for resolv.conf to change at arbitrary moments.
Examples are VPN and alternative redundant connectivity for a host. It
seems wrong for a server to rely on a static snapshot of network
configuration, because that configuration may change with time.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Bill Duetschler]

Can confirm that this bug exists on Zesty.  It occurs on my desktop
machine which has network available at boot time via cabled ethernet.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

I am using the following script saved as
/etc/resolvconf/update.d/postfix:

```
#! /bin/sh

# restart Postfix whenever resolv.conf changes, because Postfix creates
# a local copy of the file for use from inside its chroot

/usr/sbin/service postfix restart

```

That works reliably when changing network connectivity, e.g. going from
cabled Ethernet to WLAN or vice versa. It does not always work during
boot.

I use Ubuntu 14.04 LTS (and I do not dare to update my work notebook to
16.04 LTS, because it needs to actually work...).

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

As I see it, the only reliable methods found to date are described in
message #7
(https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331/comments/7),
message #17
(https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331/comments/17),
and message #19
(https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331/comments/19).

I like the idea of using a standard resolv.conf unless a more specific
one is found on Postfix startup, as proposed in #7, but that is a hack
and might lead to problems for "non-standard" DNS configurations, or
changes in the Ubuntu way of configuring DNS.

A _reliable_ way of restarting on every change of /etc/resolv.conf to
pick up the change would be the "right thing to do." AFAIU that should
be done by placing a script in /etc/resolveconf/updated.d/. That script
could possibly look just like that from message #19. I am going to try
something like that, perhaps it works. I hope resolvconf still exists in
the systemd world...

Thanks,
Erik

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Ross Patterson]

The only workaround I could get to work was to restart postifx on
network up by adding `/etc/network/if-up.d/999local` with the following
contents:

```
#!/bin/sh -e
# Called when a new interface comes up
# Local workarounds

# Fix postfix boot up issue:
# https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331
service postfix restart >/dev/null 2>&1
```

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Ross Patterson]

FWIW, I tried a bunch of different combinations of After, BindsTo,
PartOf, and ReloadPropagatedFrom in /lib/systemd/system/postfix.service
and none of them addressed the issue.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Christophe Lyon]

In case it helps other people, here is the workaround I use, in /etc/rc.local:
=
while ! grep -q nameserver /etc/resolv.conf
do
  sleep 30
done
cp /etc/resolv.conf /var/spool/postfix/etc/resolv.conf
/etc/init.d/postfix restart
=

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Mark C Davis]

Just tried this with Zesty and Postfix 3.1.4-4.  I have ipv4 dhcp, ipv6
static and resolv.conf.  After reboot /var/spool/postfix/etc/resolv.conf
did not have any addresses in it.

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

On Monday, January 30, 2017 09:33:36 PM you wrote:
> Which package was updated to fix this problem in Zesty? I could try to
> upgrade it only (I'm not ready to upgrade the whole distro).

postfix

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Christophe Lyon]

Which package was updated to fix this problem in Zesty? I could try to
upgrade it only (I'm not ready to upgrade the whole distro).

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

It would be nice if someone who is having this problem could test
3.1.4-2 or later on Zesty to see if the problem is fixed (I think it
is).

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[pataluna]

>@Marius Gedminas (mgedmin)
>Curiously, I never saw this problem on my laptop in Ubuntu versions 
>up to and including 16.04 LTS. 
>I'm seeing a lot of this problem ever since I upgraded to 16.10 LTS.

I experienced the same issues when deploying Ubuntu 16.10 to a new
MiniPC (opposed to Ubuntu 14.x that worked fine).

I have finally found an automated solution for this: enable the
NetworkManager-wait-online.service and deploy a custom script that
restarts the postfix service +-5 minutes after the machine has booted
(assuming that the wireless connection is active by then).

A. Enable this.
It is a generic approach that might be beneficial for other service than 
Postfix as well so I keep it in the script.

systemctl enable NetworkManager-wait-online.service; systemctl status 
NetworkManager-wait-online.service;


B. Add a customer Systemd timer + service
@info The timer will start ONCE, {x} minutes after the machine was booted.

nano /etc/systemd/system/mjd-restart-postfix-after-wlan-connected.timer
[Unit]
Description=(timer)mjd-restart-postfix-after-wlan-connected
[Timer]
OnBootSec=5min
[Install]
WantedBy=timers.target


nano /etc/systemd/system/mjd-restart-postfix-after-wlan-connected.service
[Unit]
Description=mjd-restart-postfix-after-wlan-connected
[Service]
Type=oneshot
ExecStart=/bin/sh -ec "systemctl restart postfix; systemctl status postfix; 
uname -a | /usr/bin/mailx -s \"Server  (`hostname`): postfix was restarted.\" 
yourem...@gmail.com"



MYUNIT=mjd-restart-postfix-after-wlan-connected
MYTIMER=${MYUNIT}.timer
systemctl enable ${MYTIMER};  systemctl status ${MYTIMER}; 
systemctl list-units --all | grep "${MYUNIT}"
systemctl status ${MYUNIT}


C. Restart
reboot
# wait 5 minutes

D. Check

MYUNIT=mjd-restart-postfix-after-wlan-connected
MYTIMER=${MYUNIT}.timer
systemctl status ${MYTIMER}


If the contents of these 2 config files (one of Resolve and one of Postfix) are 
not the same then the issue is PROBLEMATIC (Postfix started before LAN/WLAN 
gets connected).
cat /etc/resolv.conf
cat /var/spool/postfix/etc/resolv.conf


E. Info
@doc https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331
@doc https://wiki.archlinux.org/index.php/Systemd/Timers
@doc qshape deferred
@doc cat /var/log/syslog | egrep "NetworkManager|postfix"

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Re: [Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

On Monday, December 19, 2016 08:58:24 AM you wrote:
> > This is about how we integrate postfix and networking in Debian (and
> 
> thus Ubuntu). It's not an upstream issue. Removing the needs-upstream-
> report tag.
> 
> By "upstream", I meant Debian. I'm not aware of a separate bug tag for
> that. What should I be using instead of needs-upstream-report when it
> needs to go to the Debian BTS?

In this particular case, at least one of the Debian postfix maintainers reads 
Ubuntu bugs, so it's not needed.

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
  started, such as on a laptop

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Robie Basak]

> This is about how we integrate postfix and networking in Debian (and
thus Ubuntu). It's not an upstream issue. Removing the needs-upstream-
report tag.

By "upstream", I meant Debian. I'm not aware of a separate bug tag for
that. What should I be using instead of needs-upstream-report when it
needs to go to the Debian BTS?

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
  started, such as on a laptop

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Erik Auerswald]

I like the solution proposed in message #7. :-)

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

This is about how we integrate postfix and networking in Debian (and
thus Ubuntu).  It's not an upstream issue.  Removing the needs-upstream-
report tag.

** Tags removed: needs-upstream-report

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Robie Basak]

** Tags added: needs-upstream-report

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Scott Kitterman]

In the postfix service file (/lib/systemd/system/postfix.service), if
you change:

After=network.target

to:

Requires=network-online.target
After=network-online.target

does that solve your problem?

Note: this is not a general solution as it breaks setups that only
interface with localhost.

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Marius Gedminas]

I'm currently testing the following workaround:

--- /usr/lib/postfix/configure-instance.sh.orig 2016-11-14 
09:24:03.832342133 +0200
+++ /usr/lib/postfix/configure-instance.sh  2016-11-14 09:19:20.336826008 
+0200
@@ -120,6 +120,8 @@
if [ -f /${file} ]; then rm -f ${file} && cp /${file} ${file}; fi
if [ -f  ${file} ]; then chmod a+rX ${file}; fi
done
+# an empty resolv.conf is useless -- ubuntu bug LP: #1519331
+grep -q nameserver etc/resolv.conf || echo nameserver 127.0.1.1 >> 
etc/resolv.conf
# ldaps needs this. debian bug 572841
(echo /dev/random; echo /dev/urandom) | cpio -pdL --quiet . 2>/dev/null 
|| true
rm -f usr/lib/zoneinfo/localtime

It seems to work for me.

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Marius Gedminas]

Curiously, I never saw this problem on my laptop in Ubuntu versions up
to and including 16.04 LTS.  I'm seeing a lot of this problem ever since
I upgraded to 16.10 LTS.

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: postfix (Ubuntu)
   Status: New => Confirmed

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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Robie Basak]

Thank you for taking the time to report this bug and helping to make
Ubuntu better.

Importance -> Low since this doesn't affect the primary use of Postfix
as a server MTA, but only with network-manager on a desktop machine.

FWIW, I use msmtp. I can't queue mails when offline, but otherwise it
works fine for me.

It might be worth checking what the situation is on Debian for this use
case. There may be a valid bug in Debian as well, and it would be better
to follow what Debian do in this case I think.

** Summary changed:

- Mail delivery fails until restarting postfix
+ Postfix cannot resolve DNS if network was unavailable when it was started, 
such as on a laptop

** Changed in: postfix (Ubuntu)
   Importance: Undecided => Low

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  Postfix cannot resolve DNS if network was unavailable when it was
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[Bug 1519331] Re: Postfix cannot resolve DNS if network was unavailable when it was started, such as on a laptop

[Robie Basak]

Thank you for taking the time to report this bug and helping to make
Ubuntu better.

Importance -> Low since this doesn't affect the primary use of Postfix
as a server MTA, but only with network-manager on a desktop machine.

FWIW, I use msmtp. I can't queue mails when offline, but otherwise it
works fine for me.

It might be worth checking what the situation is on Debian for this use
case. There may be a valid bug in Debian as well, and it would be better
to follow what Debian do in this case I think.

** Summary changed:

- Mail delivery fails until restarting postfix
+ Postfix cannot resolve DNS if network was unavailable when it was started, 
such as on a laptop

** Changed in: postfix (Ubuntu)
   Importance: Undecided => Low

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Title:
  Postfix cannot resolve DNS if network was unavailable when it was
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