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7.2. Quick Reference
Common Exam Traps
| Trap | Correct Understanding |
|---|---|
systemctl enable vs start | enable = boot; start = now; need both for immediate + persistent |
usermod -G vs -aG | -G replaces all groups; -aG appends |
lvextend without resize2fs | LV grows but filesystem doesn't — always resize the filesystem too |
firewall-cmd without --permanent | Runtime only — lost on reload/reboot |
| SELinux Permissive mode | Logs denials but enforces NOTHING |
xfs_growfs argument | Use mount point, not device path |
rsync trailing slash | /source/ = contents; /source = directory itself |
nohup without & | Still runs in foreground — need both |
kill -9 on D state process | Cannot kill — it's waiting in kernel I/O |
git push | Pushes current branch only — not all branches |
touch /.autorelabel after recovery | Required on SELinux systems after password reset in recovery |
dd source/destination order | if= is source, of= is destination — reversed = disk destruction |
fsck on mounted filesystem | Never — will corrupt data; unmount first |
Distro Differences
| Task | RHEL/Rocky/Fedora | Debian/Ubuntu |
|---|---|---|
| Package manager | dnf | apt |
| Apache package | httpd | apache2 |
| Default firewall | firewalld | ufw |
| Default MAC | SELinux | AppArmor |
| Auth log | /var/log/secure | /var/log/auth.log |
| General log | /var/log/messages | /var/log/syslog |
| Init script dir | /etc/sysconfig/ | /etc/default/ |
| sudo group | wheel | sudo |
| Initramfs rebuild | dracut -f | update-initramfs -u |
| GRUB update | grub2-mkconfig -o /boot/grub2/grub.cfg | update-grub |
| Network config | NetworkManager / nmcli | Netplan / nmcli |
Written byAlvin Varughese
Founder•18 professional certifications