Merge pull request #5436 from thaJeztah/update_dockerd_docs

docs: add documentation for dockerd --feature flag

Author: thaJeztah

docs/reference/dockerd.md

@@ -57,6 +57,7 @@ Options:
       --exec-opt list                         Runtime execution options
       --exec-root string                      Root directory for execution state files (default "/var/run/docker")
       --experimental                          Enable experimental features
+      --feature map                           Enable feature in the daemon
       --fixed-cidr string                     IPv4 subnet for fixed IPs
       --fixed-cidr-v6 string                  IPv6 subnet for fixed IPs
   -G, --group string                          Group for the unix socket (default "docker")
@@ -971,6 +972,36 @@ Example of usage:
 }
 ```
 
+### <a name="feature"></a> Enable feature in the daemon (--feature)
+
+The `--feature` option lets you enable or disable a feature in the daemon.
+This option corresponds with the "features" field in the [daemon.json configuration file](#daemon-configuration-file).
+Features should only be configured either through the `--feature` command line
+option or through the "features" field in the configuration file; using both
+the command-line option and the "features" field in the configuration
+file produces an error. The feature option can be specified multiple times
+to configure multiple features. The `--feature` option accepts a name and
+optional boolean value. When omitting the value, the default is `true`.
+
+The following example runs the daemon with the `cdi` and `containerd-snapshotter`
+features enabled. The `cdi` option is provided with a value;
+
+```console
+$ dockerd --feature cdi=true --feature containerd-snapshotter
+```
+
+The following example is the equivalent using the `daemon.json` configuration
+file;
+
+```json
+{
+  "features": {
+    "cdi": true,
+    "containerd-snapshotter": true
+  }
+}
+```
+
 ### Daemon configuration file
 
 The `--config-file` option allows you to set any configuration option
@@ -1065,7 +1096,10 @@ The following is a full example of the allowed configuration options on Linux:
   "exec-opts": [],
   "exec-root": "",
   "experimental": false,
-  "features": {},
+  "features": {
+    "cdi": true,
+    "containerd-snapshotter": true
+  },
   "fixed-cidr": "",
   "fixed-cidr-v6": "",
   "group": "",

man/dockerd.8.md

@@ -31,6 +31,7 @@ dockerd - Enable daemon mode
 [**--exec-opt**[=*[]*]]
 [**--exec-root**[=*/var/run/docker*]]
 [**--experimental**[=**false**]]
+[**--feature**[=*NAME*[=**true**|**false**]]
 [**--fixed-cidr**[=*FIXED-CIDR*]]
 [**--fixed-cidr-v6**[=*FIXED-CIDR-V6*]]
 [**-G**|**--group**[=*docker*]]
@@ -222,6 +223,14 @@ $ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-ru
 **--experimental**=""
   Enable the daemon experimental features.
 
+**--feature**=*NAME*[=**true**|**false**]
+  Enable or disable a feature in the daemon. This option corresponds
+  with the "features" field in the daemon.json configuration file. Using
+  both the command-line option and the "features" field in the configuration
+  file produces an error. The feature option can be specified multiple times
+  to configure multiple features.
+  Usage example: `--feature containerd-snapshotter` or `--feature containerd-snapshotter=true`.
+
 **--fixed-cidr**=""
   IPv4 subnet for fixed IPs (e.g., 10.20.0.0/16); this subnet must be nested in
   the bridge subnet (which is defined by \-b or \-\-bip).