RH134 - ch04s05

System crontabs have an extra column: Username.
System crontab files in /etc/crontab and /etc/cron.d/*.
Scripts controlled by /etc/anacrontab in /etc/cron.{hourly,daily,weekly,monthly}/.

Objectives

After completing this section, students should be able to:

Schedule recurring system tasks.

Scheduling recurring system jobs with cron

System cron jobs

Apart from user cron jobs, there are also system cron jobs.

System cron jobs are not defined using the crontab command, but are instead configured in a set of configuration files. The main difference in these configuration files is an extra field, located between the Day-of-Week field and the Command field, specifying under which user a job should be run.

The /etc/crontab has a useful syntax diagram in the included comments.

 # For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

System cron jobs are defined in two locations: /etc/crontab and /etc/cron.d/*. Packages that install cron jobs should do so by placing a file in /etc/cron.d/, but administrators can also use this location to more easily group related jobs into a single file, or to push jobs using a configuration management system.

There are also predefined jobs that run every hour, day, week, and month. These jobs will execute all scripts placed in /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly/, and /etc/cron.monthly/ respectively. Please note that these directories contain executable scripts, and not cron configuration files.

Note

Make sure to make any scripts you place in these directories executable. If a script is not made executable (e.g., with chmod +x), it will not be run.

The /etc/cron.hourly/* scripts are executed using the run-parts command, from a job defined in /etc/cron.d/0hourly. The daily, weekly, and monthly jobs are also executed using the run-parts command, but from a different configuration file: /etc/anacrontab.

In the past, /etc/anacrontab was handled by a separate daemon (anacron), but in Red Hat Enterprise Linux 7, the file is parsed by the regular crond daemon. The purpose of this file is to make sure that important jobs will always be run, and not skipped accidentally because the system was turned off or hibernating when the job should have been executed.

The syntax of /etc/anacrontab is different from the other cron configuration files. It contains exactly four fields per line:

Period in days
Once per how many days this job should be run.
Delay in minutes
The amount of time the cron daemon should wait before starting this job.
Job identifier
This is the name of the file in /var/spool/anacron/ that will be used to check if this job has run. When cron starts a job from /etc/anacrontab, it will update the timestamp on this file. The same timestamp is used to check when a job has last run in the past.
Command
The command to be executed

/etc/anacrontab also contains environment variable declarations using the syntax NAME=value. Of special interest is START_HOURS_RANGE: Jobs will not be started outside of this range.

References

crond(8), crontab(1), and crontab(5), anacron(8), and anacrontab(5) man pages

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Is It possible to reset root password when the system is on multi-user.target?

jennifer1987

27 lip 2023

Hi thereWell, i have a question, Is It possible to reset root password when the system is on multi-user.target? I was not be able to found a foro o some information related with this and another question that I have, If the grub menu dont show up, is it posible to reset the root password?

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Red Hat System Administration II (RH134)

Haley_Ruccio

21 lip 2023

Build the skills to perform the key tasks needed to become a full-time Linux administratorRed Hat System Administration II (RH134) is the second part of the RHCSA training track for IT professionals who have already attended Red Hat System Administration I. The course goes deeper into core Linux system administration skills in storage configuration and management, installation and deployment of Red Hat Enterprise Linux, management of security features such as SELinux, control of recurring system tasks, management of the boot process and troubleshooting, basic system tuning, and command-line automation and productivity. This course assumes that students have attended Red Hat System Administration I (RH124).Experienced Linux administrators who seek rapid preparation for the RHCSA certification should instead start with RHCSA Rapid Track (RH199).This course is based on Red Hat Enterprise Linux 9.0.Course summaryInstall Red Hat Enterprise Linux using scalable methodsAccess security files, file systems, and networksExecute shell scripting and automation techniquesManage storage devices, logical volumes, and file systemsManage security and system accessControl the boot process and system servicesRun containersAudience for this courseThis course is geared toward Windows system administrators, network administrators, and other system administrators who are interested in supplementing current skills or backstopping other team members, in addition to Linux system administrators who are responsible for these tasks:Configuring, installing, upgrading, and maintaining Linux systems using established standards and proceduresProviding operational supportManaging systems for monitoring system performance and availabilityWriting and deploying scripts for task automation and system administrationRecommended trainingSuccessful completion of Red Hat System Administration I (RH124) is recommended.Experienced Linux administrators seeking to accelerate their path toward becoming a Red Hat Certified System Administrator should start with the RHCSA Rapid Track course (RH199).Take our free assessment to gauge whether this offering is the best fit for your skills.Technology considerationsThere are no special technology requirements.This course is not designed for bring your own device (BYOD).Internet access is not required, but is recommended to allow students to research and access Red Hat online resources.

Welcome to the Red Hat System Administration II (RH134) group in the Red Hat Learning Community!

Deanna

18 lip 2023

We are excited to launch a space dedicated to the Red Hat Training course Red Hat System Administration II! To gain the most value from this group - click the "Join Group" button in the upper right hand corner.We encourage group members to collaborate in this group to discuss topics, ask questions, share best practices and tips, provide course feedback, and share their accomplishments as it relates to RH134.Read more about Red Hat System Administration II here.

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