Docs Reference

Troubleshooting

Common problems and how to fix them.

Lantern does not start

Symptom Fix
wrote an example SNMP config … edit the credentials Normal on the first start with real devices: fill in snmp.json and start again.
listen tcp …: bind: address already in use Another program uses the port. Start on another port (Start Lantern.cmd 8080, or -addr 127.0.0.1:8080).
the SNMP collector needs a data directory NETMAP_DATA is set to an empty value. Unset it or point it at a folder.
A setting in snmp.json is rejected The message names the problem, for example discover: "10.0.0.0" is not a subnet. Subnets need a prefix length: 10.0.0.0/24.
Windows SmartScreen blocks it Preview builds are not signed yet. Check the SHA-256, then More info › Run anyway.

Devices are not polled

Open Settings › General › Polled devices (see Check collection).

  • No answer: check the address, that SNMP is enabled, the ACL allows the collector's address, and the firewall allows UDP 161. With SNMP v2c, a wrong community also shows as no answer.
  • Login failed: SNMPv3 user, protocols and passphrases must match the device exactly.
  • A device found through LLDP is not added: its management address must be inside a discover subnet. Phones and hosts are never added.
  • Enable LLDP (or CDP) on both switches. The LLDP on both ends check lists links seen from one side only.
  • A dash-dot link is inferred from one side; a dashed device is inferred, for example an unmanaged switch.

Sign-in

Problem Fix
Locked out after failed attempts Wait five minutes; throttling is per address and per username.
Forgot the only administrator's password Sign in as another administrator and reset it on the Users tab. With no other administrator: stop Lantern, rename users.json in the data folder, and start it again. It asks for a new first administrator (with the setup token from another computer). Directory and cloud accounts reappear when they next sign in; re-create other local accounts.
you are not in a group that has access Add the person to a mapped group, or add a mapping. Use Test connection (LDAP) or Try sign-in (cloud) to see their groups.
local accounts are limited to administrators Local accounts are set to Admins only; sign in with the directory or cloud account.
unknown host name; add it with -hosts Start Lantern with -hosts your.lantern.name.
Cloud sign-in says the redirect URI does not match Set Public address in Settings › Sign-in and register exactly the redirect URI shown.

See also the troubleshooting tables in LDAP and Active Directory, Microsoft Entra ID and Other OpenID Connect providers.

The page says Disconnected

The browser cannot reach the collector. The page keeps the last data it had, marks it as not current, and retries every two seconds. Check that Lantern is running (journalctl -u lantern, or lantern.log on Windows).

The page says the service is older than the page

You updated Lantern but an old copy is still running. Restart it and refresh the page.