LinuC Level 1 Exam 102Study guide

Learn the configuration files read at login and shell startup: system-wide (/etc/profile, /etc/bash.bashrc) vs per-user (~/.bash_profile, ~/.bash_login, ~/.profile, ~/.bashrc, ~/.bash_logout) and their order, command substitution with alias, setting PATH, ./source, and lists (;, &&, ||).

Learn shell scripting—the heaviest topic on exam 102 (weight 6): the shebang (#!), execute permissions (chmod, chown), positional parameters ($0, $1..$n, $#, $*, $@, shift), exit status ($?, exit), conditionals (if, case), loops (for, while), shell functions, PATH-independent scripts, and debugging (bash -x, bash -v).

Learn the foundations of TCP/IP: IP addresses, subnet masks and CIDR notation, private vs public IP addresses, the natures of TCP, UDP, and ICMP, well-known ports (22/25/53/80/123/443), and the differences between IPv4 and IPv6.

Learn to view and change host network settings: the ip command (ip addr, ip route) and legacy ifconfig/route, interface up/down (ifup, ifdown), NetworkManager's nmcli, the hostname (/etc/hostname), basic resolution files (/etc/hosts, /etc/nsswitch.conf), the default route, and reachability checks with ping.

Learn to isolate network failures: reachability (ping, ping6), path tracing (traceroute, tracepath), name resolution checks (host, dig), port/connection inspection (ss, netstat, netcat), interface reconfiguration (ifconfig, ifup/ifdown, hostname), and fixing the routing table.

Learn the DNS client settings a host uses: specifying resolvers in /etc/resolv.conf (nameserver, search), querying remote DNS servers (host, dig), the relationship with /etc/hosts, testing with getent, and changing the order via /etc/nsswitch.conf.

Learn user and group management: useradd, userdel, usermod, groupadd, groupdel, groupmod, defaults (/etc/default/useradd) and the skeleton (/etc/skel/), the account databases (/etc/passwd, /etc/shadow, /etc/group), password management with passwd, and verification with getent and id.

Learn periodic and one-shot scheduling: cron (crontab syntax, /var/spool/cron/, /etc/crontab, /etc/cron.d/, cron.{hourly,daily,weekly,monthly}), one-time at (atq, atrm), catch-up runs with anacron (/etc/anacrontab), and access control (/etc/cron.allow, /etc/cron.deny, /etc/at.allow, /etc/at.deny).

Learn language and regional settings: internationalization (i18n) vs localization (l10n), locales and their variables (LANG, LC_ALL, LC_*), the locale command, character encodings (ASCII, Unicode, UTF-8, ISO-8859, ISO-2022-JP) with iconv conversion, and why LANG=C helps in scripts.

Learn to keep and synchronize system time: date and the hardware clock (hwclock), time zone configuration (/usr/share/zoneinfo/, /etc/localtime, /etc/timezone, TZ, tzselect, timedatectl), and NTP synchronization (ntpd, ntpdate, ntpq, chronyd, chronyc, pool.ntp.org).

Learn collecting, querying, and maintaining logs: rsyslog (facilities, priorities, and actions in rsyslog.conf, forwarding to a central log server), the systemd journal (journalctl queries and filters, journald.conf, /var/log/journal/), manual entries (logger, systemd-cat), and rotation with logrotate (/etc/logrotate.conf, /etc/logrotate.d/).

Learn on-host mail delivery basics: the MTA role and major implementations (postfix, exim), system-wide forwarding in /etc/aliases applied with newaliases, per-user forwarding via ~/.forward, and the mail and mailq commands.

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).

Learn to shrink the host attack surface: shadow passwords and blocking logins with /etc/nologin, stopping unused network services (systemctl, /etc/init.d/, chkconfig, service, legacy inetd/xinetd), and firewall overview (iptables, firewalld).

Learn protecting data and communication with public-key technology: OpenSSH client key management (ssh-keygen, ssh-agent, ssh-add), the major algorithms (RSA, ECDSA, Ed25519), SSH port forwarding (local/remote), and file encryption/signing with GnuPG (gpg, gpg-agent, ~/.gnupg/).

Learn what changes for Linux servers on public clouds: the division of responsibilities with on-premises (the management console, cloud-side firewalls, routing), the meaning of region selection (domestic/foreign constraints), ephemeral storage, provider-driven maintenance and reboots, and console access paths and authentication (multi-factor authentication, one-time passwords).

Learn the definition and traits of open source and its major licenses: the freedoms to use, modify, and redistribute published source code; that OSS remains a copyrighted work offered without warranty under continuous development; and the differences among copyleft licenses (GPL, AGPL, LGPL), permissive ones (BSD, MIT, Apache License), the middle-ground MPL, and the public domain.

Learn how communities sustain open source development: communication venues (mailing lists, forums, development sites like GitHub), the structure of maintainers and contributors, and stepping into the ecosystem through use, advocacy, and bug reports.