This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
Debian Troubleshooting Guide is one symptom and one read on a Debian host you administer. Debian, not Ubuntu. Package names and the network file can differ.
Write the symptom in one sentence: what should work, what you observed, and which service or site. Then read the journal, plus /var/log/syslog and /var/log/auth.log.
AppArmor may be present. Do not disable it to make a package start. SELinux is not the Debian default. You do not reconfigure the host to see if the symptom moves.
If the hostname is wrong, stop. If the same read fails twice, stop. Do not reboot as the first step. Redact secrets before the output goes in the ticket.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.
Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Write the symptom and the hostname.
- Confirm you administer the host.
- Read one log or one status that matches the symptom.
- If a config is involved, run the config test and record the line.
- Redact secrets.
- Stop, or hand a single change to the how-to.
Mistakes that outlive the command
Debian troubleshooting goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- Changing the config to test a guess.
- The wrong host.
- Disabling a firewall or SELinux or AppArmor as a test.
- A reboot as the first step.
- A secret left in the pasted output.
- Several unrelated reads and no sentence.
Decisions to write down
One decision for Debian troubleshooting: The symptom is one sentence. The hostname matches. The first action is a read. No security control was disabled. Output with secrets is redacted. And a change, if needed, has its own how-to.
Checks before you call it done
Confirm this before you call the change done: The symptom is written. The hostname matches. One read is in the ticket. No config change was made as a test. Secrets are redacted. And the next step is one change or a stop. If one of those fails, stop.
# Troubleshoot by reading.
# Debian.
# Do not disable the firewall to test.
# Redact secrets.
# 192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.Before you leave the host
Debian Troubleshooting Guide ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.
192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.
One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.
A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a host you do not administer. You do not disable a firewall, AppArmor, or SELinux to make a check pass.
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