從 Ubuntu 18.04 -> 20.04 升級後缺少 iptables 核心模組

從 Ubuntu 18.04 升級到 20.04 (focal) 後，缺少 iptables 核心模組：

root@server:~# iptables -L
modprobe: FATAL: Module ip_tables not found in directory /lib/modules/5.4.0-42-generic
iptables v1.8.4 (legacy): can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.

我嘗試了以下方法，但沒有解決問題：

sudo apt-get install --reinstall iptables

sudo apt-get install --reinstall linux-headers-$(uname -r)

sudo dpkg-reconfigure iptables
dkms autoinstall

還安裝了 linux-modules-extra

的輸出ls -R /var/lib/dkms是：

/var/lib/dkms:
dkms_dbversion  wireguard

/var/lib/dkms/wireguard:
1.0.20200611  kernel-5.4.0-42-generic-x86_64

/var/lib/dkms/wireguard/1.0.20200611:
5.4.0-42-generic  source

/var/lib/dkms/wireguard/1.0.20200611/5.4.0-42-generic:
x86_64

/var/lib/dkms/wireguard/1.0.20200611/5.4.0-42-generic/x86_64:
log  module

/var/lib/dkms/wireguard/1.0.20200611/5.4.0-42-generic/x86_64/log:
make.log

/var/lib/dkms/wireguard/1.0.20200611/5.4.0-42-generic/x86_64/module:
wireguard.ko

有什麼想法可以重新啟動 iptables 嗎？

在我的 Ubuntu 20.04 安裝中，該文件/lib/modules/5.4.0-40-generic/kernel/net/ipv4/netfilter/ip_tables.ko屬於linux-modules包，而不是linux-modules-extra. 重新安裝linux-modules應該可以解決問題：

sudo apt-get install --reinstall linux-modules-5.4.0-42-generic

引用自：https://serverfault.com/questions/1028682