Fix several issues in "Using sysctls in a Kubernetes Cluster" (#15248)

1. Replace net.ipv4.route.min_pmtu with net.core.somaxconn in the
   example of using unsafe sysctls in containers, since the former is not
   accessible within container namespace at all.

2. Not all net.* sysctls are namespaced. Explain the correct way to
   identify the namespaced networking sysctls.

content/en/docs/tasks/administer-cluster/sysctl-cluster.md

@@ -42,9 +42,9 @@ sudo sysctl -a
 
 ## Enabling Unsafe Sysctls
 
-Sysctls are grouped into _safe_  and _unsafe_ sysctls. In addition to proper
-namespacing a _safe_ sysctl must be properly _isolated_ between pods on the same
-node. This means that setting a _safe_ sysctl for one pod
+Sysctls are grouped into _safe_ and _unsafe_ sysctls. In addition to proper
+namespacing, a _safe_ sysctl must be properly _isolated_ between pods on the
+same node. This means that setting a _safe_ sysctl for one pod
 
 - must not have any influence on any other pod on the node
 - must not allow to harm the node's health
@@ -78,13 +78,13 @@ flag of the kubelet, e.g.:
 
 ```shell
 kubelet --allowed-unsafe-sysctls \
-  'kernel.msg*,net.ipv4.route.min_pmtu' ...
+  'kernel.msg*,net.core.somaxconn' ...
 ```
 
 For {{< glossary_tooltip term_id="minikube" >}}, this can be done via the `extra-config` flag:
 
 ```shell
-minikube start --extra-config="kubelet.allowed-unsafe-sysctls=kernel.msg*,net.ipv4.route.min_pmtu"...
+minikube start --extra-config="kubelet.allowed-unsafe-sysctls=kernel.msg*,net.core.somaxconn"...
 ```
 
 Only _namespaced_ sysctls can be enabled this way.
@@ -102,7 +102,10 @@ in future versions of the Linux kernel.
 - `kernel.msg*`,
 - `kernel.sem`,
 - `fs.mqueue.*`,
-- `net.*`.
+- The parameters under `net.*` that can be set in container networking
+  namespace. However, there are exceptions (e.g.,
+  `net.netfilter.nf_conntrack_max` and `net.netfilter.nf_conntrack_expect_max`
+  can be set in container networking namespace but they are unnamespaced).
 
 Sysctls with no namespace are called _node-level_ sysctls. If you need to set
 them, you must manually configure them on each node's operating system, or by
@@ -112,8 +115,8 @@ Use the pod securityContext to configure namespaced sysctls. The securityContext
 applies to all containers in the same pod.
 
 This example uses the pod securityContext to set a safe sysctl
-`kernel.shm_rmid_forced` and two unsafe sysctls `net.ipv4.route.min_pmtu` and
-`kernel.msgmax` There is no distinction between _safe_ and _unsafe_ sysctls in
+`kernel.shm_rmid_forced` and two unsafe sysctls `net.core.somaxconn` and
+`kernel.msgmax`. There is no distinction between _safe_ and _unsafe_ sysctls in
 the specification.
 
 {{< warning >}}
@@ -131,8 +134,8 @@ spec:
     sysctls:
     - name: kernel.shm_rmid_forced
       value: "0"
-    - name: net.ipv4.route.min_pmtu
-      value: "552"
+    - name: net.core.somaxconn
+      value: "1024"
     - name: kernel.msgmax
       value: "65536"
   ...

content/zh/docs/concepts/cluster-administration/sysctl-cluster.md

@@ -34,7 +34,10 @@ $ sudo sysctl -a
 - `kernel.msg*`（内核中SystemV消息队列相关参数），
 - `kernel.sem`（内核中信号量参数），
 - `fs.mqueue.*`（内核中POSIX消息队列相关参数），
-- `net.*`（内核中网络配置项相关参数）。
+- `net.*`（内核中网络配置项相关参数），如果它可以在容器命名空间里被更改。然而，也有一些特例
+  (例如，`net.netfilter.nf_conntrack_max` 和
+  `net.netfilter.nf_conntrack_expect_max`
+  可以在容器命名空间里被更改，但它们是非命名空间的)。
 
 Sysctls中非命名空间级的被称为 _节点级_ ，其必须由集群管理员手动设置，要么通过节点的底层Linux分布方式(例如，通过 `/etc/sysctls.conf`)，亦或在特权容器中使用Daemonset。
 
@@ -71,7 +74,7 @@ Sysctls被分为 _安全的_ 和 _不安全的_ sysctls。同一节点上的pods
 sysctls。 _不安全的_ sysctls 会打上kubelet标识，在逐节点的基础上被启用，例如：
 
 ```shell
-$ kubelet --experimental-allowed-unsafe-sysctls 'kernel.msg*,net.ipv4.route.min_pmtu' ...
+$ kubelet --experimental-allowed-unsafe-sysctls 'kernel.msg*,net.core.somaxconn' ...
 ```
 
 只有 _命名空间级_ sysctls 可以使用该方法启用。
@@ -89,7 +92,7 @@ metadata:
   name: sysctl-example
   annotations:
     security.alpha.kubernetes.io/sysctls: kernel.shm_rmid_forced=1
-    security.alpha.kubernetes.io/unsafe-sysctls: net.ipv4.route.min_pmtu=1000,kernel.msgmax=1 2 3
+    security.alpha.kubernetes.io/unsafe-sysctls: net.core.somaxconn=1024,kernel.msgmax=1 2 3
 spec:
   ...
 ```

content/zh/docs/tasks/administer-cluster/sysctl-cluster.md

@@ -136,7 +136,7 @@ flag of the kubelet, e.g.:
 
 ```shell
 $ kubelet --allowed-unsafe-sysctls \
-  'kernel.msg*,net.ipv4.route.min_pmtu' ...
+  'kernel.msg*,net.core.somaxconn' ...
 ```
 <!--
 For minikube, this can be done via the `extra-config` flag:
@@ -144,7 +144,7 @@ For minikube, this can be done via the `extra-config` flag:
 如果您使用 minikube，可以通过 `extra-config` 参数来配置：
 
 ```shell
-$ minikube start --extra-config="kubelet.AllowedUnsafeSysctls=kernel.msg*,net.ipv4.route.min_pmtu"...
+$ minikube start --extra-config="kubelet.AllowedUnsafeSysctls=kernel.msg*,net.core.somaxconn"...
 ```
 <!--
 Only _namespaced_ sysctls can be enabled this way.
@@ -173,7 +173,10 @@ in future versions of the Linux kernel.
 - `kernel.msg*`,
 - `kernel.sem`,
 - `fs.mqueue.*`,
-- `net.*`.
+- `net.*`（内核中网络配置项相关参数），如果它可以在容器命名空间里被更改。然而，也有一些特例
+  (例如，`net.netfilter.nf_conntrack_max` 和
+  `net.netfilter.nf_conntrack_expect_max`
+  可以在容器命名空间里被更改，但它们是非命名空间的)。
 
 <!--
 Sysctls with no namespace are called _node-level_ sysctls. If you need to set
@@ -190,11 +193,11 @@ applies to all containers in the same pod.
 
 <!--
 This example uses the pod securityContext to set a safe sysctl
-`kernel.shm_rmid_forced` and two unsafe sysctls `net.ipv4.route.min_pmtu` and
+`kernel.shm_rmid_forced` and two unsafe sysctls `net.core.somaxconn` and
 `kernel.msgmax` There is no distinction between _safe_ and _unsafe_ sysctls in
 the specification.
 --->
-此示例中，使用 Pod SecurityContext 来对一个安全的 sysctl 参数 `kernel.shm_rmid_forced` 以及两个非安全的 sysctl 参数 `net.ipv4.route.min_pmtu`和 `kernel.msgmax` 进行设置。在 Pod 规格中对 _安全的_ 和 _非安全的_ sysctl 参数不做区分。
+此示例中，使用 Pod SecurityContext 来对一个安全的 sysctl 参数 `kernel.shm_rmid_forced` 以及两个非安全的 sysctl 参数 `net.core.somaxconn`和 `kernel.msgmax` 进行设置。在 Pod 规格中对 _安全的_ 和 _非安全的_ sysctl 参数不做区分。
 
 {{< warning >}}
 <!--
@@ -214,8 +217,8 @@ spec:
     sysctls:
     - name: kernel.shm_rmid_forced
       value: "0"
-    - name: net.ipv4.route.min_pmtu
-      value: "552"
+    - name: net.core.somaxconn
+      value: "1024"
     - name: kernel.msgmax
       value: "65536"
   ...