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Cybersecurity Triage

Read-only

Find Held Packages Blocking Patches

Patch simulation shows kept-back packages and you need to see whether apt holds are part of the reason.

Command

apt-mark showhold | sed 's/^/held: /'

Before you run this

System impact: Read-only. Low when scoped to the shown target.

When not to use it: Do not remove holds automatically; confirm why each package was held and who owns the risk.

Expected output

Held package names prefixed with held: for quick review.

System impact

Read-only. Nothing changes. apt-mark prints held package names and sed labels them for incident notes.

Recovery / rollback: no state is changed.

When to use it

Use before blaming repositories, mirrors, or dependency conflicts for missing security updates.

When not to use it

Do not remove holds automatically; confirm why each package was held and who owns the risk.

next steps

Related commands

Cybersecurity Triage Read-only

Prove a Package Candidate Is From Security

The package name is not enough; the candidate repository tells the patch story.

apt-cache policy openssl | sed -n '/Installed:/p;/Candidate:/p;/security/p'
Cybersecurity Triage Dry run

Dry-Run Unattended Security Upgrades

Unattended upgrades can explain what they would patch before they patch it.

unattended-upgrade --dry-run --debug 2>&1 | sed -n '/Packages that will be upgraded:/,/^$/p'
Cybersecurity Triage Read-only

Check Whether Patches Require Reboot

Some security fixes are not complete until the host boots the new kernel or libraries.

test -f /var/run/reboot-required && printf 'reboot-required\n' && cat /var/run/reboot-required.pkgs
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.

  • LPIC-1 style command-line practice
  • LFCS style performance-task practice
  • Linux+ style troubleshooting review

Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.