Chapter 5 · Security·v1.0.0·Updated 7/6/2026·~13 min
What's changed: Initial version (topic 1.10, subtopics 1.10.1–1.10.4)
5.1Performing Security Administration Tasks
Key points
Learn routine host security checks: auditing SUID/SGID files (find -perm), password aging (chage, passwd, usermod), discovering open ports (ss, netstat, nmap, lsof, fuser), login visibility (who, w, last), resource limits (ulimit), sudo (/etc/sudoers, su), and auto-logout (TMOUT).
Security is recurring inspection work, not set-and-forget. This section stocks the audit toolbox: find dangerous files, manage account expiry, count open doors, and see who is inside.
5.1.1File audits and password aging
- Audit SUID/SGID with
find / -perm -4000(SUID) and-perm -2000(SGID). Unexpected SUID files are privilege-escalation fuel—inventory them regularly (applying 2.1 knowledge). - Password aging via chage (
chage -l user01shows status;-M 90= 90-day maximum;-d 0= force change at next login). passwd and usermod offer some equivalents. - Login visibility: who (current logins), w (plus activity and load), last (login history, from /var/log/wtmp).
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