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Cybersecurity Triage

Read-only

List Users with Login Shells

You need to list accounts with shell-like login programs.

Command

awk -F: '$7 ~ /sh$/ {print $1, $7}' etc/passwd

Before you run this

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

When not to use it: Do not disable accounts from this output alone; confirm ownership and operational use first.

Expected output

Usernames and login shells for accounts ending in sh.

System impact

Read-only. Nothing changes. The command reads account records and prints shell users.

Recovery / rollback: no state is changed.

When to use it

Use during account inventory, server handoff, or first-response checks.

When not to use it

Do not disable accounts from this output alone; confirm ownership and operational use first.

next steps

Related commands

Cybersecurity Triage Sensitive output

Find SSH Keys for nologin Users

A nologin shell does not automatically mean SSH keys are irrelevant.

comm -12 <(awk -F: '$7 !~ /(bash|sh|zsh)$/ {print $1}' /etc/passwd | sort) <(find /home -path '*/.ssh/authorized_keys' -printf '%h\n' 2>/dev/null | awk -F/ '{print $(NF-1)}' | sort)
Cybersecurity Triage Read-only

List Accounts with Login Shells

Login shells are the first account inventory to review.

awk -F: '$7 ~ /(bash|sh|zsh)$/ {printf "%s %s\n", $1, $7}' /etc/passwd
Cybersecurity Triage Sensitive output

Find Password-Enabled Accounts

A shell account with an unlocked password hash deserves extra attention.

sudo awk -F: '$2 !~ /^(!|\*)/ {print $1}' /etc/shadow
Cybersecurity Triage Sensitive output

Find SSH Key Users with sudo

The highest-priority access review starts where SSH keys and sudo overlap.

comm -12 <(find /home -path '*/.ssh/authorized_keys' -printf '%h\n' 2>/dev/null | awk -F/ '{print $(NF-1)}' | sort) <(awk -F: '$1=="sudo" {gsub(",","\n",$4); print $4}' /etc/group | sort)
Cybersecurity Triage Sensitive output

Extract SSH AllowUsers Accounts

AllowUsers turns SSH access into an explicit account list.

awk '/^AllowUsers/ {for (i = 2; i <= NF; i++) print $i}' etc/ssh/sshd_config
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.