nfsroot boot crash after systemd-networkd starts

Posted on Edited on In Views: Word count in article: 209 Reading time ≈ 1 mins.

Yesterday we found that nfsroot will get crash after systemd-networkd starts:

1
nfs: server 192.168.0.101 not responding, still trying

Root cause

Crash was happened after we importing eth.network for systemd-networkd, which will set ethernet as DHCP mode after system booting. We doubting that this setting will release the IP we set when boards was mounting nfsroot.

Solutions

As far as I know there are two solutions to avoid systemd-networkd breaking nfs connection:

  • KernelCommandLine=!nfsroot
1
2
3
4
5
6
7
[Match]
Name=eth0
KernelCommandLine=!nfsroot

[Network]
DHCP=ipv4

According to Linux manual page:

  KernelCommandLine=
      Checks whether a specific kernel command line option is set (or
      if prefixed with the exclamation mark unset). See
      "ConditionKernelCommandLine=" in systemd.unit(5) for details.

So KernelCommandLine=!nfsroot will prevent this config to be applied if we have set nfsroot in kernel command line.

  • CriticalConnection=true
1
2
3
4
5
6
7
8
9
[Match]
Name=eth0

[Network]
DHCP=ipv4

[DHCP]
CriticalConnection=true

According to Linux manual page:

   CriticalConnection=
      When true, the connection will never be torn down even if the
      DHCP lease expires. This is contrary to the DHCP specification,
      but may be the best choice if, say, the root filesystem relies on
      this connection. Defaults to false.

So with CriticalConnection=true the connection will not be dropped, which prevent nfs from disconnecting as well.