RH134 Red Hat System Administration II notes in the margin

tags: `red hat, rhel8`

You will find here notes and links to official docs with information on products and technologies that described on RedHat Training.
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Course description: RH134 Red Hat System Administration II

:memo: Table of contents

RH134 Red Hat System Administration II notes in the margin
- :memo: Table of contents

1. Improve command line productivity

Run commands more efficiently by using advanced features of the Bash shell, shell scripts, and various utilities provided by Red Hat Enterprise Linux.

Book: Introduction to Linux

Book: Advanced Bash-Scripting Guide
Книга: Искусство программирования на языке сценариев командной оболочки

#!/bin/bash
# this sample script is ping computers in loop. 
# It uses conditional expression with color echo

for HOST in f{1..7}
do 
  echo -en "\nlets try ping $HOST: "
  if ping -c 1 -W 1 $HOST >/dev/null 2>&1
   then
    echo -e "\e[1;32m alive \e[0m" 
   else
    echo -e "\e[1;41m DEAD \e[0m"
  fi
done

YouTube Video: "Where GREP Came From - Computerphile" with Brian Kernighan

GNU website: GNU Grep 3.5 manual

Почему работать в консоли настолько приятно? Так задумано отцами-основателями Unix

Image Not Showing Possible Reasons

The image file may be corrupted
The server hosting the image is unavailable
The image path is incorrect
The image format is not supported

Learn More →

2. Schedule future tasks

Schedule commands to run in the future, either one time or on a repeating schedule.

Cron в Linux: история, использование и (внутреннее) устройство
Red Hat Enterprise Linux 7 System Administrator’s Guide: CHAPTER 24. AUTOMATING SYSTEM TASKS

Techmint Article: Cron Vs Anacron: How to Schedule Jobs Using Anacron on Linux
Putorius Article: Cron vs Anacron - Different Ways of Scheduling Jobs on Linux

Cron	Anacron
It’s a daemon	It’s not a daemon
Appropriate for server machines	Appropriate for desktop/laptop machines
Enables you to run scheduled jobs every minute	Only enables you to run scheduled jobs on daily basis
Doesn’t executed a scheduled job when the machine if off	If the machine if off when a scheduled job is due, it will execute a scheduled job when the machine is powered on the next time
Can be used by both normal users and root	Can only be used by root unless otherwise (enabled for normal users with specific configs)

Fedora Magazine: Systemd Timers for Scheduling Tasks

Let's create an alternative for this crontab job:
*/10 * * * * /usr/bin/date >> /tmp/date
Timers work directly with services' units. So we have to create /etc/systemd/system/date.service first:
[Unit]
Description=Prints date into /tmp/date file

[Service]
Type=oneshot
ExecStart=/usr/bin/sh -c '/usr/bin/date >> /tmp/date'
Then we have to create timer unit with the same name but with *.timer suffix /etc/systemd/system/date.timer:
[Unit]
Description=Run date.service every 10 minutes

[Timer]
OnCalendar=*:0/10

[Install]
WantedBy=timers.target
This config will run date.service every 10 minutes. You can also list all timers enabled in your system using systemctl list-timers command or systemctl list-timers –all to list all timers. Run systemctl start date.timer to enable timer.

You can also create timer with different name, i.e. task.timer. In this case you have specify service unit name:
Unit=date.service

Freedesktop man page: systemd.timer — Timer unit configuration
Freedesktop man page: systemctl — Control the systemd system and service manager

RedHat Knowledgebase: Why are there many tmpfs filesystems mounted on the server?
RedHat Knowledgebase: How to work with /dev/shm in Red Hat Enterprise Linux 7 and later
RedHat Knowledgebase: How do I restrict or modify size of /dev/shm?

RedHat Knowledgebase: How do I modify the size of tmpfs?
By default tmpfs is half of available system RAM

What Is /dev/shm And Its Practical Usage

Freedesktop man journald.conf: journald disk usage can grow up to 4GB

https://www.loggly.com/ultimate-guide/managing-journal-size/
https://www.loggly.com/ultimate-guide/linux-logging-with-systemd/#journald-configuration

3. Tune system performance

Improve system performance by setting tuning parameters and adjusting scheduling priority of processes.
Tuned is a system tuning service for Linux.

RedHat Blog: Tuning Your System With Tuned

RHEL8 Docs: Monitoring and managing system status and performance: CHAPTER 2. GETTING STARTED WITH TUNED

RHEL8 Docs: Monitoring and managing system status and performance: CHAPTER 3. CUSTOMIZING TUNED PROFILES

YouTube Video: Linux processes, init, fork/exec, ps, kill, fg, bg, jobs

4. Control access to files with ACLs

Interpret and set access control lists (ACLs) on files to handle situations requiring complex user and group access permissions.

5. Manage SELinux security

Protect and manage the security of a server by using SELinux.
Manage basic storage
https://people.redhat.com/dwalsh/
https://danwalsh.livejournal.com/
YouTube: Red Hat Summit: Are you listening to what SELinux is telling you?

Image Not Showing Possible Reasons

The image file may be corrupted
The server hosting the image is unavailable
The image path is incorrect
The image format is not supported

Learn More →

SELinux Coloring Book

https://selinuxproject.org/page/Category:Notebook
https://freecomputerbooks.com/The-SELinux-Notebook-The-Foundations.html
https://www.amazon.com/SELinux-System-Administration-Sven-Vermeulen/dp/1787126951
https://www.amazon.com/SELinux-Example-Using-Security-Enhanced/dp/0131963694
https://www.amazon.com/Selinux-Source-Security-Enhanced-Linux/dp/0596007167

6. Create and manage storage devices, partitions, file systems, and swap spaces from the command line.

https://www.thomas-krenn.com/en/wiki/Linux_Storage_Stack_Diagram

RHEL8 Docs: Considerations in adopting RHEL 8: Btrfs has been removed

12.1.1. Btrfs has been removed
The Btrfs file system has been removed in Red Hat Enterprise Linux 8. 
This includes the following components:

- The btrfs.ko kernel module
- The btrfs-progs package
- The snapper package
You can no longer create, mount, or install on Btrfs file systems in 
Red Hat Enterprise Linux 8. The Anaconda installer and the Kickstart 
commands no longer support Btrfs.

7. Manage logical volumes

Create and manage logical volumes containing file systems and swap spaces from the command line.

RHEL8 Docs: Configuring and managing logical volumes

The Status of Storage Within Linux: LVM, Btrfs, and ZFS comparison

8. Implement advanced storage features

Manage storage using the Stratis local storage management system and use VDO volumes to optimize storage space in use.

Stratis Project

https://opensource.com/article/18/4/stratis-easy-use-local-storage-management-linux
https://opensource.com/article/18/4/stratis-lessons-learned

RHEL8 Docs: Managing file systems: Chapter 17. Managing layered local storage with Stratis

Red hat Interactive Lab: Stratis

RHEL8 Docs: Deduplicating and Compressing storage

https://www.redhat.com/en/blog/introducing-virtual-data-optimizer-reduce-cloud-and-premise-storage-costs

Red hat Interactive Lab: VDO

https://www.opennet.ru/opennews/art.shtml?num=51828

9. Access network-attached storage

Use the NFS protocol to administer network-attached storage.

RHEL8 Docs: System Design Guide Chapter: 29. Mounting NFS shares
RHEL8 Docs: Considerations in adopting RHEL 8 Chapter 12. File systems and storage

https://www.kernel.org/doc/html/latest/filesystems/autofs.html
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/nfs-autofs

https://www.freedesktop.org/software/systemd/man/systemd.automount.html
https://www.freedesktop.org/software/systemd/man/systemd.mount.html

Альтернатива демону autofs.Автомонтирование при помощи, юнитов systemd mount и automount.

Habr: Автомонтирование файловых систем с systemd

cat /etc/systemd/system/media-nfs.mount
[Unit]
Description=NFS share
[Mount]
What=server.url.example.com:/srv/nfs_share
Where=/media/nfs
Type=nfs4
Options=rw
DirectoryMode=0755


cat /etc/systemd/system/media-nfs.automount
[Unit]
Description=NFS share
Requires=network-online.target
[Automount]
Where=/media/nfs
TimeoutIdleSec=301
[Install]
WantedBy=graphical.target