[config]: Add hostname command to config CLI (sonic-net#669)

Signed-off-by: Sangita Maity <sangitamaity0211@gmail.com>

config/main.py

@@ -556,6 +556,25 @@ def load_minigraph():
     click.echo("Please note setting loaded from minigraph will be lost after system reboot. To preserve setting, run `config save`.")
 
 
+#
+# 'hostname' command
+#
+@config.command('hostname')
+@click.argument('new_hostname', metavar='<new_hostname>', required=True)
+def hostname(new_hostname):
+    """Change device hostname without impacting the traffic."""
+
+    config_db = ConfigDBConnector()
+    config_db.connect()
+    config_db.mod_entry('DEVICE_METADATA' , 'localhost', {"hostname" : new_hostname})
+    try:
+        command = "service hostname-config restart"
+        run_command(command, display_cmd=True)
+    except SystemExit as e:
+        click.echo("Restarting hostname-config  service failed with error {}".format(e))
+        raise
+    click.echo("Please note loaded setting will be lost after system reboot. To preserve setting, run `config save`.")
+
 #
 # 'portchannel' group ('config portchannel ...')
 #

doc/Command-Reference.md

@@ -221,6 +221,7 @@ This command lists all the possible configuration commands at the top level.
     acl                    ACL-related configuration tasks
     bgp                    BGP-related configuration tasks
     ecn                    ECN-related configuration tasks
+    hostname               Change device hostname without impacting traffic
     interface              Interface-related configuration tasks
     interface_naming_mode  Modify interface naming mode for interacting...
     load                   Import a previous saved config DB dump file.
@@ -1636,6 +1637,26 @@ The list of the WRED profile fields that are configurable is listed in the below
 
 Go Back To [Beginning of the document](#SONiC-COMMAND-LINE-INTERFACE-GUIDE) or [Beginning of this section](#ECN-Configuration-And-Show-Commands)
 
+# Update Device Hostname Configuration Commands
+
+This sub-section of commands is used to change device hostname without traffic being impacted.
+
+**config hostname <new_hostname>**
+This command is used to change device hostname without traffic being impacted.
+
+- Usage: config hostname [OPTIONS] <new_hostname>
+
+        Change device hostname without impacting the traffic.
+ Options:
+  -?, -h, --help  Show this message and exit.
+
+- Examples:
+  ```
+  admin@lnos-x1-a-csw06:~$ sudo config hostname CSW06
+  Running command: service hostname-config restart
+  Please note loaded setting will be lost after system reboot. To preserve setting, run `config save`.
+  ```
+
 # Interface Configuration And Show-Commands
 
 ## Interface Show Commands