Linux Survival Basics
Read-onlyShow Failed systemd Units
A VPS feels unhealthy, but checking services one by one wastes time and misses failed timers, mounts, and sockets.
Command
systemctl --failed --no-pagerBefore you run this
System impact: Read-only. Low when scoped to the shown target.
When not to use it: Do not use it as the only health check; a service can be running but still misconfigured or returning bad responses.
Expected output
Failed unit rows such as backup.service or app-worker.service.
System impact
Read-only. Nothing changes. The command prints units whose current systemd state is failed.
Recovery / rollback: no state is changed.
When to use it
Use after deploys, reboots, package upgrades, or alerts when you need the fastest systemd health snapshot.
When not to use it
Do not use it as the only health check; a service can be running but still misconfigured or returning bad responses.
next steps
Related commands
Show Failed Mount Units
systemd often records mount failures as failed units.
systemctl --failed --no-pager
Read the Failure Cause in systemctl Status
The status page often tells you the failed startup step before you open every log.
systemctl status app-worker --no-pager --lines=50
Map systemd Timers to Services
A timer is only half the scheduled job. The service is the payload.
systemctl list-timers --all --no-pager --plain | awk 'NR==1 || /\.timer/ {print $(NF-1), "->", $NF}'
Show a Service LimitNOFILE
A shell ulimit is not the service limit.
systemctl show nginx -p LimitNOFILE --no-pager
Compare Failure Output With the Effective Unit
Put the failed step next to the unit config that created it.
systemctl status app-worker --no-pager --lines=50 && systemctl cat app-worker
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.