Configuring network interfaces with netplan on Ubuntu, and testing changes without losing the connection

Goal

Change a static IP, route or bonding setup on Ubuntu 22.04/24.04 through netplan without risking a lockout on a remote box.

Prerequisites

Root access; know which renderer is active (networkd is the default on Server, NetworkManager on Desktop); a session type that survives a brief network blip (console access is safer than SSH for the final apply).

Steps

1. Locate the existing configuration, normally one file under /etc/netplan/*.yaml. Netplan's YAML reference notes the renderer key names "the tool that will be used to set up your configuration. Valid values are networkd and NetworkManager", defaulting to networkd when unset.
2. Edit or add a file with the desired settings, for example a static address:

   network:
     version: 2
     ethernets:
       eth0:
         addresses: [192.0.2.10/24]
         routes:
           - to: default
             via: 192.0.2.1
         nameservers:
           addresses: [192.0.2.1]
   

3. Keep the YAML files readable by root only (chmod 600 /etc/netplan/*.yaml); current netplan warns about world-readable files because they can hold Wi-Fi keys and other secrets. Validate syntax without applying: netplan generate, which renders the backend configuration into a temporary location and fails loudly on a YAML or schema error.
4. On any session where a mistake could cut connectivity, use netplan try instead of netplan apply directly. netplan try "takes a netplan configuration, applies it, and automatically rolls it back if the user does not confirm the configuration within a time limit" (120 seconds by default, changeable with --timeout).
5. Confirm by pressing Enter within the timeout; if the session is already lost, do nothing — the automatic revert restores the previous configuration.
6. Once confirmed, run netplan apply if you edited further, then verify with ip addr show eth0 and ip route.

Expected result

ip addr shows the new address immediately after a confirmed netplan try/apply; a wrong configuration reverts on its own within the timeout and connectivity returns without manual recovery.

Limits and test basis

Some configurations (STP-enabled bridges, for instance) can take over a minute to settle, which the tool's own known-issues note flags as a case where the default timeout may be too short. No reboot is required; a re-login may be needed only if the change altered the interface used for the current session. Debian's classic alternative, ifupdown, keeps interface definitions in /etc/network/interfaces instead of YAML, applied with ifup/ifdown rather than a renderer; it has no equivalent try-and-rollback command, so changes there should be tested from console access directly.