Linux Labs

User administration and sudo

Accounts, memberships, and restricted delegation.

Disks and filesystems

Blocks and inodes, sparse files, finding what uses the space, and mounting you can verify.

Logical volumes and snapshots

LVM layers, growing a volume with its ext4, snapshot space and the limits of a rollback.

A new disk

A disk with no filesystem, the partition table, a labelled ext4 and an fstab entry by UUID with nofail.

Packages and software installation

Archives and installed packages, dependencies, indexes, the package database record, installing, upgrading and removing.

Users and permissions

Identity, file and directory permissions, and focused repairs.

Schedules and logs

Selecting journal records, cron jobs and systemd timers, log rotation and journal retention.

Backup and recovery

What goes into a tar archive, where files land on extraction, how to check a copy, how rsync picks files and where --delete acts.

Help and the shell

Arguments, help, expansion, and PATH.

Text and editors

Reading tools and verification of edits.

Quiz: CPU, memory and OOM

The load average, the R and D states, the CPU queue and nice; free and available, the OOM killer within a service ceiling and drop-ins.

Quiz: DNS and SSH

Check how you find the cause when a name will not resolve or SSH will not let you in.

Quiz: git for configuration

What was changed in a config and by whom, how to get the working version back without rewriting history, and how to update a server's working copy while keeping a local edit.

Quiz: nginx

How nginx picks a site and a file, and where to look for the cause of a proxy's 502.

Quiz: PostgreSQL

A refused connection stage by stage — network, the pg_hba.conf rule, the password — and a dump restored into a separate database.

Quiz: TLS

A certificate's expiry, name and issuer, reissuing with the same key, the chain in nginx and the redirect to HTTPS.

Quiz: addresses and routes

Interface addresses and prefixes, route selection and persistent network configuration with Netplan.

Quiz: logins and passwords

Password policy with pwquality, login lockout with faillock, a fail2ban jail on the systemd journal and checking the ban.

Quiz: boot and time

The boot chain and the start queue, unit ordering and dependencies, systemd-analyze verify, the zone in a cron schedule, chrony and stepping the clock.

Quiz: a container from the inside

Image and container, the main process and docker logs, port publishing, the environment and the restart policy.

Quiz: limits and kernel parameters

Process and service limits, LimitNOFILE in a drop-in, kernel parameters and sysctl.d, waiting for the disk, iostat, pidstat and ionice.

Quiz: navigation and paths

Absolute and relative paths, moving between directories, hidden names and finding a file.

Quiz: reliable scripts

Exit statuses, curl checks, set -euo pipefail, a script in a timer's service and an flock lock.

Quiz: several containers

How containers find each other by name, and how to bring up, fix and take down a docker compose stack.

Quiz: images and data

Building an image from a Dockerfile, layers, tags and the build cache; where a container keeps data — the container layer, a volume, a host directory — and the permissions on its files.

Quiz: confinement and audit

A service as root and its confinement with User= and systemd, an AppArmor denial and a profile edit, an audit rule and finding who changed a file.

Quiz: file operations

Check the resulting state after creation, copying, and moving.

Quiz: your first commands and Linux components

Check your understanding of system components and command output.

Quiz: first playbooks

An inventory and the UNREACHABLE answer, ad-hoc commands and the CHANGED and SUCCESS statuses, a module playbook, a handler, a template and a trial run.

Quiz: searching and editing text

How to find lines with a pattern, change them with sed without an editor and add up a column with awk.

Quiz: ports and firewall

Who listens on a port and on which address, refusal, timeout and error answers, nftables rules for a single source.

Quiz: streams and pipelines

Where a command's output and errors go, and how to answer a question with a pipeline.

Quiz: processes and signals

Find the right process, free the terminal, and stop a program so that it saves its work.

Quiz: terminal workflow

Check editing, history, paging, and interruption.

Quiz: resources and security

Exit code 137 and OOMKilled, the --memory and --cpus limits, docker stats, the process user and --user.

Quiz: networking between hosts

Check how you find the side and the stage of a fault when a service does not answer a neighbouring machine.

Quiz: scripts

How to run a script, pass it arguments with spaces, test files and answer with an exit status.

Quiz: systemd services

Service state and autostart, restarts after a crash, diagnosing a failure and applying a unit change.

Quiz: what a process is doing

strace and system calls, /proc/<PID>/fd and lsof, kernel messages about ext4 errors, segfaults and OOM.

Quiz: what a server exposes

An inventory of listening services, binding to 127.0.0.1, a default-drop nftables filter, deleted files after an upgrade and needrestart.