CS AO case studies

CS AO · Put your knowledge to work in context.

The Certified Specialist Administrator (CS AO) is a vendor-neutral, multiple-choice credential aimed at people who run and maintain server or platform systems day to day: junior-to-mid-level system administrators, infrastructure engineers broadening their scope, and support staff moving into an operations role. It validates that you can reason about a live estate rather than recite trivia - covering system administration fundamentals, installation and deployment, user and access management, storage and file systems, networking and connectivity, security and hardening, monitoring, backup and recovery, and structured troubleshooting. The CS AO case studies are 5 cases and about 5,306 words.

/var is full but du says 61 GB - the deleted-inode decision

app-prod-07 runs RHEL 9 with /var as a 500 GB ext4 filesystem on an LVM logical volume. At 02:14 the on-call engineer receives an alert: filesystem /var at 100 percent.

1,022 words, about 5 min 2

Departed contractor, a shared deploy account, and a two-hour Sunday window

Acme's platform team runs 180 Ubuntu 22.04 virtual machines. Authentication is centralised in FreeIPA, but sudo rules are still local files in /etc/sudoers.d and engineers' SSH public keys live in each user's ~/.ssh/authorized keys.

1,043 words, about 5 min 3

MTU 9000 database, MTU 1500 API tier, and an ICMP block

Your team runs a three-tier application in a single datacentre. Web servers on 10.20.10.0/24 call api servers on 10.20.11.0/24, which open PostgreSQL connections to db-prod-01 at 10.20.20.15:5432.

1,074 words, about 5 min 4

Backup window overrun, an 82 percent repository, and an RTO nobody has tested

backup-prod-01 runs nightly backups of a PostgreSQL database of 1.2 TB and a 6 TB NFS file share to a deduplicating appliance whose repository is 82 percent full and growing about 1.2 TB per month after deduplication. The job window is 22:00 to 04:00 over a single 1 GbE link.

1,104 words, about 6 min 5

Six weeks to the QSA: patching, root SSH, auditd, SELinux, and a vendor who will not move

Forty RHEL 8 servers run a vendor-supplied Java application in cardholder-data scope. A CIS Level 1 scan puts the fleet at 64 percent compliance.

1,063 words, about 5 min