FAILOVER(8)

NAME

failover - UPS Failover Driver

SYNOPSIS

failover -h

failover -a UPS_NAME [OPTIONS]

Note	This man page only documents the specific features of the failover driver. For information about the core driver, see nutupsdrv(8).

DESCRIPTION

The failover driver acts as a smart proxy for multiple "real" UPS drivers. It connects to and monitors these underlying UPS drivers through their local UNIX sockets (or Windows named pipes), continuously evaluating health and suitability for "primary" duty according to a set of user configurable rules and priorities.

At any given time, failover designates one UPS driver as the primary, and presents its commands, variables and status to the outside world as if it were directly talking to that UPS. From the perspective of the clients (such as upsmon(8) or upsc(8)), the failover driver behaves like any single UPS, abstracting away the underlying redundancy, and allowing for seamless transitioning between all monitored UPS drivers and their datasets.

The driver dynamically promotes or demotes the primary UPS driver based on:

Socket availability and communication status
Data freshness and UPS online/offline indicators
User-defined status filters (e.g., presence or absence of OL, LB, …)
Administrative override via control commands (force.primary, force.ignore)

If the current primary becomes unavailable or no longer meets the criteria, the driver automatically fails over to a more suitable driver. During transitions, it ensures that any data is switched out instantly, without the upsd(8) considering it as stale or the clients acting on any previously degraded status.

When no suitable primary is available, a configurable fallback state is entered:

Keep last primary and declare the data as stale
Raise ALARM and declare the data as stale
Raise ALARM and set forced shutdown (FSD)

Different communication media can be used to connect to individual UPS drivers (e.g., USB, Serial, Ethernet). failover communicates directly at the socket level and therefore does not rely on upsd(8) being active.

EXTRA ARGUMENTS

This driver supports the following settings:

port=drivername-devicename,drivername2-devicename2,…

Required. Specifies the local sockets (or Windows named pipes) of the underlying UPS drivers to be tracked. Entries must either be a path or follow the format drivername-devicename, as used by NUT’s internal socket naming convention (e.g. usbhid-ups-myups). Multiple entries are comma-separated with no spaces.

inittime=seconds

Optional. Sets a grace period after driver startup during which the absence of a primary is tolerated. This allows time for underlying drivers to initialize. For networked connections or drivers that require "lock-picking" their communication protocol, consider increasing this value to accommodate potential longer delays. Defaults to 30 seconds.

deadtime=seconds

Optional. Sets a grace period in seconds after which a non-responsive UPS driver is considered dead. Defaults to 30 seconds.

relogtime=seconds

Optional. Time interval in which repeated connection failure logs are emitted for a UPS, reducing log spam during unstable conditions. Defaults to 5 seconds.

noprimarytime=seconds

Optional. Duration to wait without a suitable primary UPS driver before entering the configured fallback mode (fsdmode). Defaults to 15 seconds.

maxconnfails=count

Optional. Number of consecutive connection failures allowed per UPS driver before entering into the cooldown period (coolofftime). Defaults to 5.

coolofftime=seconds

Optional. Cooldown period during which the driver pauses reconnect attempts after exceeding maxconnfails. Defaults to 15 seconds.

fsdmode=0|1|2

Optional. Defines the behavior when no suitable primary UPS driver is found after noprimarytime has elapsed. Defaults to 0.

0: Do not demote the last primary, but mark its data as stale. This is similar to how a regular UPS driver would behave when it loses its connection to the target UPS device. upsmon(8) will act on the last known (online or not) status, and decide itself whether that UPS should be considered critical.
1: Demote the primary, raise ALARM, and mark the data as stale after an additional few seconds have elapsed (ensuring full propagation). This will cause upsmon(8) to detect that a device previously in an alarm state has lost its connection, consider the UPS driver critical, and possibly trigger a forced shutdown (FSD) due to depletion of MINSUPPLIES.
2: Demote the primary, raise ALARM, and immediately set FSD. This will set FSD from the driver side and preempt upsmon(8) from raising it itself. This mode is for setups where immediate shutdown is warranted, regardless of anything else, and getting FSD out to the clients as fast as just possible.

checkruntime=0|1|2|3

Optional. Controls how battery.runtime values are used to break ties between non-fully-online UPS devices at priority 3 or lower. Has no effect on initial priority selection or when strictfiltering is enabled. Defaults to 1.

0: Disabled. No runtime comparison is done. The first candidate with the best priority is selected according to the order of the port argument.
1: Compare battery.runtime. The UPS with the higher value is preferred. If the value is missing or invalid, the UPS cannot win the tie-break.
2: Compare battery.runtime.low. The UPS with the higher value is preferred. If the value is missing or invalid, the UPS cannot win the tie-break.
3: Compare both variables strictly. The UPS is preferred only if it has both a higher battery.runtime and battery.runtime.low value. If either is missing or invalid, the UPS cannot win the tie-break.

strictfiltering=0|1

Optional. If set to 1, only UPS drivers matching the configured status filters are considered for promotion to primary. If set to 0, the hard-coded default logic is also considered when no status filters match (read more about this in the section PRIORITIES). Defaults to 0.

status_have_any=OL,CHRG,…

Optional. If any of these comma-separated tokens are present in a UPS driver’s ups.status, it passes this status filtering criteria. Defaults to unset.

status_have_all=OL,CHRG,…

Optional. All listed comma-separated tokens must be present in ups.status for the UPS driver to pass this status filtering criteria. Defaults to unset.

status_nothave_any=OB,OFF,…

Optional. If any of these comma-separated tokens are present in ups.status, the UPS driver does not pass this status filtering criteria. Defaults to unset.

status_nothave_all=OB,LB,…

Optional. If all of these comma-separated tokens are present in ups.status, the UPS driver does not pass this status filtering criteria. Defaults to unset.

Note

The status_* arguments are primarily intended to adjust the weighting of UPS drivers, allowing some to be prioritized over others based on their status. For example, a driver reporting OL might be preferred over one reporting ALARM OL. While strictfiltering can be enabled, status filters are most effective when used in combination with the default set of connectivity-based PRIORITIES. For more details, see the respective section further below.

IMPLEMENTATION

The port argument in the ups.conf(5) should reference the local driver sockets (or Windows named pipes) that the "real" UPS drivers are using. A basic default setup with multiple drivers could look like this:

  [realups]
     driver = usbhid-ups
     port = auto

  [realups2]
     driver = usbhid-ups
     port = auto

  [failover]
     driver = failover
     port = usbhid-ups-realups,usbhid-ups-realups2

Any upsmon(8) clients would be set to monitor the failover UPS.

The driver fully supports setting variables and performing instant commands on the currently elected primary UPS driver, which are proxied and with end-to-end tracking also being possible (upscmd(1) and upsrw(1) -w). You may notice some variables and commands will be prefixed with upstream., this is to clearly separate the upstream commands from those of failover itself.

For your convenience, additional administrative commands are exposed to directly influence and override the primary election process, e.g. for maintenance:

<socketname>.force.ignore [seconds] prevents the specified UPS driver from being selected as primary for the given duration, or permanently if a negative value is used. A value of 0 resets this override and re-enables selection.
<socketname>.force.primary [seconds] forces the specified UPS driver to be treated with the highest priority for the given duration, or permanently if a negative value is used. A value of 0 resets this override.

Calling either command without an argument has the same effect as passing 0, but only for that specific override - it does not affect the other.

PRIORITIES

As outlined above, primaries are dynamically elected based on their current state and according to a strict set of user influenceable priorities, which are:

0 (highest): UPS driver was forced to the top by administrative command.
1: UPS driver has passed the user-defined status filters.
2: UPS driver has fresh data and is online (in status OL).
3: UPS driver has fresh data, but may not be fully online.
4 (lowest): UPS driver is alive, but may not have fresh data.

The UPS driver with the highest calculated priority is chosen as primary, ties are resolved through order of the socket names given within the port argument.

For the user-defined status filters, the following internal order is respected:

status_nothave_any (first)
status_have_all
status_nothave_all
status_have_any (last)

If strictfiltering is enabled, priorities 2 to 4 are not applicable.

If no user-defined status filters are set, the priority 1 is not applicable.

Note	The base requirement for any election is the UPS socket being connectable and the UPS driver having published at least one full batch of data during its lifetime. UPS driver not fulfilling that requirement are always disqualified.

RATIONALE

In complex power environments, presenting a single, consistent source of UPS information to upsmon(8) is sometimes preferable to monitoring multiple independent drivers directly. The failover driver serves as a bridge, allowing upsmon(8) to make decisions based on the most suitable available data, without having to interpret conflicting inputs or degraded sources.

Originally designed for use cases such as dual-PSU systems or redundant communication paths to a single UPS, failover also supports more advanced setups - for example, when multiple UPSes feed a shared downstream load (via STS/ATS switches), or when drivers vary in reliability. In these cases, the driver can be combined with external logic or scripting to dynamically adjust primary selection and facilitate graceful degradation. Such setups may also benefit from further integration with the clone family of drivers, such as clone(8) or clone-outlet(8), for greater granularity and monitoring control down to the outlet level.

Additionally, in more niche scenarios, some third-party NUT integrations or graphical interfaces may be limited to monitoring a single UPS device. In such cases, failover can help by exposing only the most relevant or highest-priority data source, allowing those tools to operate within their constraints without missing critical information.

Ultimately, this driver enables more nuanced power monitoring and control than binary online/offline logic alone, allowing administrators to respond to degraded conditions early - before they escalate into critical events or require upsmon(8) to take action.

LIMITATIONS

When using failover for redundancy between multiple UPS drivers connected to the same underlying UPS device, data is not multiplexed between the drivers. As a result, some data points may be available in some drivers but not in others.

For checkruntime considerations, the unit of both battery.runtime and battery.runtime.low is assumed to be seconds. UPS drivers that report these values using different units are considered non-compliant with the NUT variable standards and should be reported to the NUT developers as faulty.

AUTHOR

Sebastian Kuttnig <sebastian.kuttnig@gmail.com>