Round 3: Troubleshooting¶
The troubleshooting round starts with a symptom and no instructions. Interviewers score the path more than the final answer: whether the candidate asks the right questions, forms hypotheses, and checks the cheapest and most likely causes first.
Method¶
- Restate the symptom in one sentence and confirm it: what fails, for whom, since when.
- Ask clarifying questions that split the problem: one user or all, always or since a change, one host or many.
- Form two or three hypotheses and say which is most likely and why.
- Check in order of cost: read-only commands first (
getent,id,journalctl,ss,df), changes last. - Fix the proven cause only, then verify with the same command that found it.
- Name the prevention: the control that stops a repeat.
Changing things before reading the evidence loses points
Restarting services, chmod 777 or setenforce 0 as a first step suggests guessing. Say what you would look at first, and what each result would mean.
Scenario Index¶
| Scenario | Symptom as asked | Modules |
|---|---|---|
| Cannot Log In or Use Sudo | "A user cannot log in, and another gets an error from sudo." | 04 Users and Access |
| Binary Won't Execute | "We copied tools to a new server and none of them run." | 01 Shell and CLI, 06 Package Management |
| Process Won't Die | "We ran kill -9 and the process is still there." | 07 Processes |
| Service Won't Start | "We deployed the new service and systemctl start fails." | 08 Systemd and Services, 09 Logging |
| Cron Job Not Running | "The script works when I run it, but the scheduled job produces nothing." | 01 Shell and CLI, 10 Scheduling |
| Disk Full | "The log says No space left on device, and deleting the big log did not help." | 02 Files and Filesystem, 07 Processes, 12 Storage |
| DNS Not Resolving | "The app cannot resolve api.shop.internal, but the DNS team says their server answers." | 13 Networking |
| Cannot SSH | "I can't SSH to the box that worked yesterday." | 14 SSH, 15 Security |
| Service Unreachable | "The service works on the server but clients can't connect." | 13 Networking, 15 Security |
| Cannot Reach Host | "This host can't reach another one on the network." | 13 Networking, 15 Security |
| TLS Certificate Errors | "curl fails on our internal HTTPS site with a certificate error." | 13 Networking, 15 Security |
| Permission Denied | "The app logs Permission denied on a file it should be able to read." | 05 Permissions, 12 Storage, 15 Security |
| Suspected Compromise | "This server is behaving strangely and we think it's compromised." | 07 Processes, 13 Networking, 15 Security |
| Server Slow | "The server feels slow. Everything is sluggish. Figure out why." | 07 Processes, 17 Performance |
| Too Many Open Files | "The app is logging Too many open files and dropping connections." | 02 Files and Filesystem, 17 Performance |
| Cannot Fork | "Every command says fork: retry: Resource temporarily unavailable." | 07 Processes, 17 Performance |
| Boot Failure | "The server was rebooted and never came back." | 12 Storage, 16 Boot and Recovery |
| High Load, Low CPU | "Load average is 40 but the CPUs are almost idle." | 07 Processes, 17 Performance, 18 Network Storage |
| High Memory and OOM | "This service keeps getting killed with exit code 137." | 07 Processes, 17 Performance, 19 Containers |