** Description changed:
+ [ Impact ]
+
+ nfs-server.service (part of the nfs-utils package) has insufficient
+ dependencies to start correctly in a setting where the NFS exports list
+ contains DNS hostnames (not in local hosts file) or netgroups served via
+ network (for example sssd).
+
+ This issue can negatively impact users that, for example, cannot easily
+ resort to using IP addresses directly in the /etc/exports file, and need
+ to use hostnames instead in order to be able to mount NFS shares over
+ the network.
+
+ [ Test Case ]
+
+ You can reproduce the issue by following the instructions below. Adjust
+ the Ubuntu release on "images:ubuntu/hirsute" accordingly.
+
+ $ lxc launch images:ubuntu/hirsute nfs-utils-bug1918141 --vm
+ $ lxc shell nfs-utils-bug1918141
+ # apt update
+ # apt install -y nfs-kernel-server
+ # mkdir /testshare
+ # cat >> /etc/exports << EOF
+ /testshare ubuntu.com(ro,sync,no_subtree_check)
+ EOF
+ # systemctl edit --full systemd-networkd.service
+
+ You will have to:
+
+ - Comment out the "Wants=" line.
+ - Remove "network.target" from the "Before=" line.
+ - Add a new "After=fakenet.service" line.
+ - Add a new "Wants=fakenet.service" line.
+ - Add the following line in the "[Service]" section:
+
+ ExecStartPre=/bin/sleep 10
+
+ # systemctl edit --force --full fakenet.service
+
+ This new service file will contain:
+
+ [Unit]
+ Description=Fake network.target
+ DefaultDependencies=no
+ After=systemd-udevd.service network-pre.target systemd-sysusers.service
systemd-sysctl.service
+ Before=network.target multi-user.target shutdown.target
+ Conflicts=shutdown.target
+ Wants=network.target
+
+ [Service]
+ Type=oneshot
+ ExecStart=/bin/true
+
+ [Install]
+ WantedBy=multi-user.target
+
+ # systemctl enable fakenet.service
+ # systemctl disable systemd-resolved
+ # systemctl mask systemd-resolved
+ # rm /etc/resolv.conf
+ # cat > /etc/resolv.conf << EOF
+ nameserver 8.8.8.8
+ EOF
+ # reboot
+
+ After a few seconds, you can enter the VM again:
+
+ $ lxc shell nfs-utils-bug1918141
+ # sleep 20 && systemctl status nfs-server.service
+ ● nfs-server.service - NFS server and services
+ Loaded: loaded (/lib/systemd/system/nfs-server.service; enabled; vendor
preset: enabled)
+ Active: active (exited) since Tue 2021-03-16 20:51:42 UTC; 39s ago
+ Process: 310 ExecStartPre=/usr/sbin/exportfs -r (code=exited,
status=0/SUCCESS)
+ Process: 311 ExecStart=/usr/sbin/rpc.nfsd $RPCNFSDARGS (code=exited,
status=0/SUCCESS)
+ Main PID: 311 (code=exited, status=0/SUCCESS)
+
+ Mar 16 20:51:41 nfs-utils-bug1918141 systemd[1]: Starting NFS server and
services...
+ Mar 16 20:51:41 nfs-utils-bug1918141 exportfs[310]: exportfs: Failed to
resolve ubuntu.com
+ Mar 16 20:51:41 nfs-utils-bug1918141 exportfs[310]: exportfs: Failed to
resolve ubuntu.com
+ Mar 16 20:51:42 nfs-utils-bug1918141 systemd[1]: Finished NFS server and
services.
+
+ As you can see, the service was started but exportfs failed to resolve
+ the hostname.
+
+ [Where problems could occur]
+
+ This fix has been applied upstream for quite a while now, and is even
+ part of a release, so it has been extensively tested by users and other
+ distributions that have more recent nfs-utils. I cannot easily envision
+ problems with the proposed changes but:
+
+ * If the user has manually modified the nfs-server.service file without
+ taking proper precautions (i.e., editin the file directly on
+ /lib/systemd/system/ instead of using "systemctl edit"), then he might
+ experience a conflict when installing a new version of the file, and his
+ modifications will be lost. However, this falls under the "local
+ configuration issue", in my opinion.
+
+ [ Original Description ]
+
nfs-server.service has insufficient dependencies to start correctly in a
setting where the nfs exports list contains DNS host names (not in local
hosts file) or netgroups served via network (for example sssd).
Typical failures listed by systemctl status nfs-server.service are:
Mar 08 14:16:52 server.example.com exportfs[844]: exportfs: Failed to resolve
client1.example.com
Mar 08 14:16:52 server.example.com exportfs[844]: exportfs: Failed to resolve
client2.example.com
-
- Our workaround is to add the appropriate dependecies in
/etc/systemd/system/nfs-server.service.d/dependencies.conf like so:
+ Our workaround is to add the appropriate dependecies in
+ /etc/systemd/system/nfs-server.service.d/dependencies.conf like so:
----------------------8<----------------------------
[Unit]
# nfs-server.service runs exportfs on startup, thus we need to be able to
# do host and netgroup lookups which requires network to be online.
After=network-online.target nss-lookup.target nss-user-lookup.target
----------------------8<----------------------------
While nfs-server.service do depend on network.target, that only means
that the network has been configured. On physical hardware it can take
significantly longer for the network to come online (8+ seconds for our
10G NICs). Also note that we configure static IP:s via systemd-networkd,
things might behave differently when using DHCP, network-manager etc. In
any case, depending on network.target is almost always wrong, and
network-online.target is usually the right one.
nss-lookup.target is needed to ensure that DNS resolution works, and
nss-user-lookup.target is the best approximation to ensure that netgroup
resolution via sssd or equivalent works. Usually things "just works"
even without these dependencies, but to ensure correct startup they
should be present.
It should be noted that this seems to once have been fixed in Ubuntu,
but has been lost along the way for quite some time. When googling I
find for example https://code.launchpad.net/~ubuntu-branches/ubuntu/wily
/nfs-utils/wily-201507271018/+merge/265946 that fixes the network.target
vs network-online.target dependency, but it has since been lost in the
wind it seems.
** Also affects: nfs-utils (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: nfs-utils (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: nfs-utils (Ubuntu Hirsute)
Importance: Undecided
Assignee: Sergio Durigan Junior (sergiodj)
Status: Confirmed
** Also affects: nfs-utils (Ubuntu Groovy)
Importance: Undecided
Status: New
** Changed in: nfs-utils (Ubuntu Bionic)
Status: New => Confirmed
** Changed in: nfs-utils (Ubuntu Focal)
Status: New => Confirmed
** Changed in: nfs-utils (Ubuntu Groovy)
Status: New => Confirmed
** Changed in: nfs-utils (Ubuntu Bionic)
Assignee: (unassigned) => Sergio Durigan Junior (sergiodj)
** Changed in: nfs-utils (Ubuntu Groovy)
Assignee: (unassigned) => Sergio Durigan Junior (sergiodj)
** Changed in: nfs-utils (Ubuntu Focal)
Assignee: (unassigned) => Sergio Durigan Junior (sergiodj)
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https://bugs.launchpad.net/bugs/1918141
Title:
nfs-server.service needs name resolution and network online
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