4Essential System Services

• 4.1Managing System Time

  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).

• 4.2System Logging

  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/).

• 4.3Mail Transfer Agent (MTA) Basics

  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.