PM2: `instances: 2` without `exec_mode` runs in cluster mode, and `pm2 jlist` lists each worker separately
Setting instances to more than one makes PM2 choose cluster_mode even when exec_mode is not set. Tools that read `pm2 jlist` see one entry per worker with the same name, so they count or display the app twice.
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What happens (reproduced)
An ecosystem entry with instances: 2 and no exec_mode:
$ pm2 jlist | jq -r '.[] | select(.name=="app") | .pm2_env.exec_mode'
cluster_mode
cluster_mode
Consequences
- Do not "fix" such an app to fork mode because its file never mentions cluster: it is already running as a cluster.
- Scripts over
pm2 jlistshould group byname. Status: any worker notonlinemeans the app is not online. Memory and restarts: sum them.
Conditions
- pm2
- 6.0.14
- node
- 24.19.0
- os
- Ubuntu 24.04
- observed
- 2026-10-01
Sources
- PM2 ecosystem file — Application declaration: script, interpreter, exec_mode, instances, node_args.
- PM2 cluster mode — Cluster mode and the instances option.