Resolv.conf overwritten by rubbish

sredna · 2017-05-02 10:30:54

Hi,

Since some time, I have had problems with resolv.conf. Nameservers from dhcp is not present in the file. I use NetworkManager and the setup is pretty standard.

[anders@archie ~]$ cat /etc/NetworkManager/NetworkManager.conf
# Configuration file for NetworkManager.
# See "man 5 NetworkManager.conf" for details.
dhcp=dhclient
dns=default

# Configuration for resolvconf(8)
# See resolvconf.conf(5) for details

resolv_conf=/etc/resolv.conf
# Anders: append google nameserver, workaround brokenness.
name_servers_append=8.8.8.8

# If you run a local name server, you should uncomment the below line and
# configure your subscribers configuration files below.
#name_servers=127.0.0.1

If I restart NetworkManager I initially get this (before the network connection is finished):

# Generated by resolvconf
domain bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5
nameserver 8.8.8.8

But after the connection is finished, it is rewritten to this:

[anders@archie ~]$ cat /etc/resolv.conf
# Generated by resolvconf
domain bbsyd.net
search bbsyd.net uvnet.itcfyn.adm
nameserver 127.0.0.1

So first, resolvconf writes the file as expected, but then later something (NetworkManager?) overwrites it.
Any hints on why this happens, and how to prevent it?

mrunion · 2017-05-02 12:32:13

Show us a list all the services you have running.

sredna · 2017-05-02 13:57:28

Hi mrunion, thanks for answering. I hope this is sufficient. My eyes fell on pdnsd, which I have now stopped, disabled and removed.

[anders@archie ~]$ systemctl -t service -a list-units
UNIT LOAD ACTIVE SUB DESCRIPTION
alsa-restore.service loaded active exited Save/Restore Sound Card State
alsa-state.service loaded inactive dead Manage Sound Card State (restore and store)
● auditd.service not-found inactive dead auditd.service
bluetooth.service loaded active running Bluetooth service
dbus.service loaded active running D-Bus System Message Bus
dm-event.service loaded inactive dead Device-mapper event daemon
emergency.service loaded inactive dead Emergency Shell
getty@tty1.service loaded inactive dead Getty on tty1
getty@tty2.service loaded active running Getty on tty2
getty@tty3.service loaded active running Getty on tty3
kmod-static-nodes.service loaded active exited Create list of required static device nodes for the current kernel
ldconfig.service loaded inactive dead Rebuild Dynamic Linker Cache
logrotate.service loaded inactive dead Rotate log files
lvm2-lvmetad.service loaded inactive dead LVM2 metadata daemon
man-db.service loaded inactive dead Update man-db cache
mkinitcpio-generate-shutdown-ramfs.service loaded inactive dead Generate shutdown-ramfs
● NetworkManager-wait-online.service loaded failed failed Network Manager Wait Online
NetworkManager.service loaded active running Network Manager
● pdnsd.service loaded failed failed proxy name server
● plymouth-quit-wait.service not-found inactive dead plymouth-quit-wait.service
● plymouth-quit.service not-found inactive dead plymouth-quit.service
● plymouth-start.service not-found inactive dead plymouth-start.service
polkit.service loaded active running Authorization Manager
rescue.service loaded inactive dead Rescue Shell
rtkit-daemon.service loaded active running RealtimeKit Scheduling Policy Service
sddm.service loaded active running Simple Desktop Display Manager
shadow.service loaded inactive dead Verify integrity of password and group files
● syslog.service not-found inactive dead syslog.service
systemd-ask-password-console.service loaded inactive dead Dispatch Password Requests to Console
systemd-ask-password-wall.service loaded inactive dead Forward Password Requests to Wall
systemd-backlight@backlight:intel_backlight.service loaded active exited Load/Save Screen Backlight Brightness of backlight:intel_backlight
systemd-binfmt.service loaded inactive dead Set Up Additional Binary Formats
systemd-firstboot.service loaded inactive dead First Boot Wizard
systemd-fsck-root.service loaded inactive dead File System Check on Root Device
systemd-fsck@dev-disk-by\x2duuid-07DE\x2d36F2.service loaded active exited File System Check on /dev/disk/by-uuid/07DE-36F2
systemd-hwdb-update.service loaded inactive dead Rebuild Hardware Database
systemd-initctl.service loaded inactive dead /dev/initctl Compatibility Daemon
systemd-journal-catalog-update.service loaded inactive dead Rebuild Journal Catalog
systemd-journal-flush.service loaded active exited Flush Journal to Persistent Storage
systemd-journald.service loaded active running Journal Service
systemd-logind.service loaded active running Login Service
systemd-machine-id-commit.service loaded inactive dead Commit a transient machine-id on disk
systemd-modules-load.service loaded active exited Load Kernel Modules
systemd-quotacheck.service loaded inactive dead File System Quota Check
systemd-random-seed.service loaded active exited Load/Save Random Seed
systemd-remount-fs.service loaded active exited Remount Root and Kernel File Systems
systemd-rfkill.service loaded inactive dead Load/Save RF Kill Switch Status
systemd-sysctl.service loaded active exited Apply Kernel Variables
systemd-sysusers.service loaded inactive dead Create System Users
systemd-timesyncd.service loaded active running Network Time Synchronization
systemd-tmpfiles-clean.service loaded inactive dead Cleanup of Temporary Directories
systemd-tmpfiles-setup-dev.service loaded active exited Create Static Device Nodes in /dev
systemd-tmpfiles-setup.service loaded active exited Create Volatile Files and Directories
systemd-udev-trigger.service loaded active exited udev Coldplug all Devices
systemd-udevd.service loaded active running udev Kernel Device Manager
systemd-update-done.service loaded inactive dead Update is Completed
UNIT LOAD ACTIVE SUB DESCRIPTION
alsa-restore.service loaded active exited Save/Restore Sound Card State
alsa-state.service loaded inactive dead Manage Sound Card State (restore and store)
● auditd.service not-found inactive dead auditd.service
bluetooth.service loaded active running Bluetooth service
dbus.service loaded active running D-Bus System Message Bus
dm-event.service loaded inactive dead Device-mapper event daemon
emergency.service loaded inactive dead Emergency Shell
getty@tty1.service loaded inactive dead Getty on tty1
getty@tty2.service loaded active running Getty on tty2
getty@tty3.service loaded active running Getty on tty3
kmod-static-nodes.service loaded active exited Create list of required static device nodes for the current kernel
ldconfig.service loaded inactive dead Rebuild Dynamic Linker Cache
logrotate.service loaded inactive dead Rotate log files
lvm2-lvmetad.service loaded inactive dead LVM2 metadata daemon

Ropid · 2017-05-02 15:03:53

You can take a look at what NetworkManager etc. sent to resolvconf like this:

resolvconf -l

What do you see when you take a look at that before and after NetworkManager does its thing?

sredna · 2017-05-02 15:43:34

Here is a sequence:

[anders@archie ~]$ sudo systemctl restart NetworkManager
[sudo] adgangskode for anders: 
[anders@archie ~]$ resolvconf -l                        
# resolv.conf from wlp2s0.dhcp
# Generated by dhcpcd from wlp2s0.dhcp
domain bbsyd.net
search bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5

[anders@archie ~]$ resolvconf -l
# resolv.conf from wlp2s0.dhcp
# Generated by dhcpcd from wlp2s0.dhcp
domain bbsyd.net
search bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5

# resolv.conf from NetworkManager
# Generated by NetworkManager
search bbsyd.net
nameserver 127.0.0.1
nameserver 212.10.10.4
nameserver 212.10.10.5

[anders@archie ~]$ cat /etc/resolv.conf
# Generated by resolvconf
domain bbsyd.net
nameserver 127.0.0.1
[anders@archie ~]$

Looks weird, as the actual content is not equal to the output of resolvconf -l.

Last edited by sredna (2017-05-02 15:44:06)

Ropid · 2017-05-02 16:45:09

Yes, and it also ignores your "name_server_append=8.8.8.8" in the config. It's perhaps some program editing the /etc/resolv.conf file directly without going through resolvconf?

sredna · 2017-05-02 16:47:41

Yes, but what could it be??? That is the question

Ropid · 2017-05-02 17:44:59

I found a package "fatrace" in the AUR that can record file accesses of all running processes on the machine and works with the normal Arch kernel. It records everything and can't watch just a certain file, but you can filter with grep, so you could use it like this to track resolv.conf while you restart NetworkManager:

sudo fatrace | grep /etc/resolv\.conf

sredna · 2017-05-02 17:48:57

I ended up uninstalling openresolv (which provides resolvconf), since it is not required, and now I get a working resolv.conf:

[root@archie ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search bbsyd.net
nameserver 127.0.0.1
nameserver 212.10.10.4
nameserver 212.10.10.5
[root@archie ~]#

I still do not understand why the nameservers were removed.

rsmarples · 2017-05-03 09:34:01

sredna wrote:

Here is a sequence:

[anders@archie ~]$ sudo systemctl restart NetworkManager
[sudo] adgangskode for anders: 
[anders@archie ~]$ resolvconf -l                        
# resolv.conf from wlp2s0.dhcp
# Generated by dhcpcd from wlp2s0.dhcp
domain bbsyd.net
search bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5

[anders@archie ~]$ resolvconf -l
# resolv.conf from wlp2s0.dhcp
# Generated by dhcpcd from wlp2s0.dhcp
domain bbsyd.net
search bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5

# resolv.conf from NetworkManager
# Generated by NetworkManager
search bbsyd.net
nameserver 127.0.0.1
nameserver 212.10.10.4
nameserver 212.10.10.5

[anders@archie ~]$ cat /etc/resolv.conf
# Generated by resolvconf
domain bbsyd.net
nameserver 127.0.0.1
[anders@archie ~]$

Looks weird, as the actual content is not equal to the output of resolvconf -l.

Here's the key part

# resolv.conf from NetworkManager
# Generated by NetworkManager
search bbsyd.net
nameserver 127.0.0.1
nameserver 212.10.10.4
nameserver 212.10.10.5

So NetworkManager inserted a local nameserver.
Because of this, resolvconf will just list that in /etc/resolv.conf - the expectation is that this local name server will then have the rest of the DNS setup. But this requries exta config in resolvconf.conf, because it does not know what local resolver is in use or where it should store it's config files.
Luckily, you can configure openresolv to ignore this in resolvconf.conf like so

replace="nameserver/127.0.0.1/"

That will make the applied NetworkManager config look like this

# resolv.conf from NetworkManager
# Generated by NetworkManager
search bbsyd.net
nameserver 212.10.10.4
nameserver 212.10.10.5

Exactly the same, but the local name server removed.

Last edited by rsmarples (2017-05-03 09:35:12)

sredna · 2017-05-03 16:08:44

Thanks, but I did not find that in the manuals. Nor do I understand why NetworkManager adds a local nameserver - I did not knowingly ask it to, and no local nameserver is running. I can't figure out why. I did at one time experiment with running pdnsd, but that was a long time ago, som somewhere, NetworkManager is getting things wrong, even if it is just failing to document how to configure it properly.

rsmarples · 2017-05-03 16:44:16

The replace option is specified in resolvconf.conf(5).

Arch Linux

#1 2017-05-02 10:30:54

Resolv.conf overwritten by rubbish

#2 2017-05-02 12:32:13

Re: Resolv.conf overwritten by rubbish

#3 2017-05-02 13:57:28

Re: Resolv.conf overwritten by rubbish

#4 2017-05-02 15:03:53

Re: Resolv.conf overwritten by rubbish

#5 2017-05-02 15:43:34

Re: Resolv.conf overwritten by rubbish

#6 2017-05-02 16:45:09

Re: Resolv.conf overwritten by rubbish

#7 2017-05-02 16:47:41

Re: Resolv.conf overwritten by rubbish

#8 2017-05-02 17:44:59

Re: Resolv.conf overwritten by rubbish

#9 2017-05-02 17:48:57

Re: Resolv.conf overwritten by rubbish

#10 2017-05-03 09:34:01

Re: Resolv.conf overwritten by rubbish

#11 2017-05-03 16:08:44

Re: Resolv.conf overwritten by rubbish

#12 2017-05-03 16:44:16

Re: Resolv.conf overwritten by rubbish

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