Linux Administrative Tasks

Scheduling Jobs with Cron

• Cron is a daemon that runs continuously and wakes up every minute to check tables for tasks to execute.
• These tables are known as crontabs and contain cron jobs.
• Cron is suitable for servers and systems that are constantly powered on.
• Each cron job is executed only if the system is running at the scheduled time.
• Cron can be used by ordinary users, each of whom has their own crontab, as well as the root user who manages system crontabs.

Alternative to Cron

• Anacron is suitable for systems that can be powered off (such as desktops or laptops).
• Anacron can only be used by root.

Localisation and Internationalisation

• Linux distributions can be configured to use custom localisation settings.
• These settings include region and language related definitions such as time zone, interface language, and character encoding.
• Applications rely on environment variables, system configuration files, and commands to decide the proper time and language to use.
• Adjustments to time and localisation settings are important for user experience and correct timing of system events.

File Permissions and Security

• /etc/passwd and /etc/group files are world readable and are shadowed for security reasons.
• When shadow passwords are used, an x is seen in the second field of these files.
• Encrypted passwords for users and groups are stored in /etc/shadow and /etc/gshadow, which are readable only by root and members belonging to the shadow group.

Cron and at Jobs Management

• Cron and at jobs can be managed by configuring user access to cron and at services.
• systemd timer units can be used to manage cron and at jobs.
• Files used for cron and at jobs management include /etc/cron.{d,daily,hourly,monthly,weekly}/, /etc/at.deny, /etc/at.allow, /etc/crontab, /etc/cron.allow, /etc/cron.deny, and /var/spool/cron/.