RHEL Tutor

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What New Feature added in REHL 8

Overview

RHEL 8 is based on Fedora 28 and uses upstream Linux kernel 4.18. This release provides a stable, secure and good foundation for hybrid cloud deployments to support customer’s workloads.

Architectures

Red Hat Enterprise Linux 8 provides support for following architectures.

1. AMD and Intel 64-bit architectures

2. The 64-bit ARM architecture

3. IBM Power Systems, Little Endian

4. IBM Z

New features in RHEL 8

1. RHEL 8 developer friendly means fewer efforts needed for setup or configuration. A developer can start working on codes easily without wasting many efforts in setting up the environment for it.

2. RHEL 8 is based on Fedora 28 and uses upstream Linux kernel 4.18 and kernel name is Ootpa.

3. RHEL 8 comes with pre-enabled the two main repositories: BaseOS and Application Stream (AppStream)

4. Linux containers included in the bag.

5. cockpit is available by default in RHEL repos. Cockpit is a web-based tool used by the sysadmin to manage systems.

6. KDE environment is removed from RHEL 8

7. GNOME v3.28 is added in RHEL 8.

8. RHEL 8 uses Wayland as default display server instead

of X.org

9. Startis is new volume management tool introduced.

10. XFS file system now supports shared copy on write data extents functionality.

11. LUKS2 encryption format (default) introduced which replaces legacy LUKS1 format.

12. DNF is rolling out behind YUM v4.

13. RPM v4.14 is distributed in RHEL 8 which validates entire package contents before starting an installation.

14. iptables are replaced by nftables.

15. OpenLDAP is no more available.

16. It has composer included. Its used to deploy custom images in the cloud.

17. Few software versions upgraded in RHEL 8 are Python 3.6, Nginx 1.14, Apache 2.4.35, PHP 7.2, Ruby 2.5, Perl 5.26, Databases like MariaDB 10.3, MySQL 8.0, PostgreSQL 10, PostgreSQL 9.6, and Redis 4.0

18. OS content is available through pre-enabled repository BaseOS.

19. In RHEL 7 supports 64TB of physical ram but RHEL8 Supports up to 4PB of physical memory.

20. nfsnobody user replaced by nobody.

21. KVM supports 5 level paging, increasing physical and virtual address space used by host or guest.

22. OpenSSH package has been upgraded to 7.8p1, and it removed the support for SSH version 1 protocol.

23. RHEL 8 now comes with qemu-kvm v2.12. This version provides few enhancements like UEFI guest boot, vCPU hot plug and hot unplug, guest I/O threading and Q35 machine type.

24. Removal of Btrfs filesystem support from RHEL8.

Thanks.....!!

Shutdown,Reboot, suspend and hibernation the system

Redhat Linux,Cent OS and Oracle Linux Machine Shutdown,Reboot,Suspend and hibernate commands.

There are many commands are available to shutdown and reboot .

To shutdown the system:

init 0
poweroff
halt
shutdown -h now
systemctl poweroff
systemctl halt
telinit 0

To reboot the system:

init 6
reboot
shutdown -r now
systemctl reboot
telinit 6

To suspend the system:

systemctl suspend

To put the system into hibernation:

systemctl hibernate

Linux file command with example

file command is used to determine the file type. It does not care about the extension used for file. It simply uses file command and tell us the file type. It has several options.

Syntax:

file <filename>

1) How to determine the file type of a file

# file Karun.txt

File.txt: ASCII text

2)How to determine filesystem type of partition using file command

the -s flag enables reading of block or character files .

# file –s /dev/sda1

/dev/sda1: SGI XFS filesystem data (blksz 4096, inosz 256

, v2 dirs)

cal command in Linux with example

About cal

The cal command displays a simple, formatted calendar in your terminal.

If no options are specified, cal display the current month in your terminal, with the current day highlighted.

1. To Print Current month calendar

cal

2. Display previous/current/next month calendar using single command

cal -3

3. To Display particular month of the year calendar

cal -m 12

4. Print number of days in year using -j option

cal -m 12

5. Display the calendar for December of this year.

cal -m 12

6. To Display specified year calendar

cal 2010

How to set Hardware Clock Date Time using hwclock command

How to set Hardware Clock Date Time using hwclock command

hwclock is a utility for accessing the hardware clock, also referred to as the Real Time Clock (RTC). The hardware clock is independent of the operating system you use and works even when the machine is shut down. This utility is used for displaying the time from the hardware clock.

Hardware clock is also called as BIOS clock. You can change the date and time of the hardware clock from the BIOS.

The hardware clock stores the values of: year, month, day, hour, minute, and second. It is not able to store the time standard, local time or Coordinated Universal Time (UTC), nor set the Daylight Saving Time (DST).

1. Display Hardware Clock Date and Time

Just type hwclock, which will display the date and time of your system’s hardware clock. This is the same date and time that you’ll see from the BIOS screen. You can also use option -r, or –show to display the date and time.

# hwclock
Sat 18 Aug 2018 08:26:12 AM PDT  -0.312862 seconds

# hwclock -r
Sat 18 Aug 2018 08:20:54 AM PDT  -0.109748 seconds

# hwclock --show
Sat 18 Aug 2018 08:21:12 AM PDT  -0.640982 seconds

2. Set Hardware Clock Date and Time Manually

To Set the Hardware Clock to a Specific Date and Time

The following will set the date to Aug 11th, 2013. Please note that if you don’t specify the time, it will be set to 12:00:00 AM.

# hwclock --set --date 8/19/2018

# hwclock
Sun 19 Aug 2018 12:00:04 AM PDT  -0.703489 seconds

You can also set both date and time at the same time as shown below. Please note that it will use the local time by default.

# hwclock --set --date "8/19/2018 23:10:45"

# hwclock
Sun 19 Aug 2018 11:10:48 PM PDT  -0.562862 seconds

3. Copy System Time to Hardware Time

You really want to make sure your hardware clock has the same date and time as the system clock. As you see currently there is a difference between the system clock and hardware clock time.

# date
Sat Aug 18 08:16:17 PDT 2018

# hwclock
Sat 18 Aug 2018 08:26:53 AM PDT  -0.687841 seconds

So, use the hwclock command as shown below to set the hardware clock same as system clock.

hwclock --systohc

How to set and view system date & time using date command

How to set and view system date & time using date command

date command is used to display the system date and time. date command is also used to set date and time of the system.

1. To display the current date and local time, type the following at a shell prompt:

# date

Mon Sep 17 17:30:24 EDT 2018

2. To display the current date and time in UTC, type the following at a shell prompt:

 # date -u

Mon Sep 17 17:30:24 UTC 2018

3. To change the current date & time, run the date command with the --set or -s option as root:

# date –s ’17-sep-2018 17:00’

4. To change the current time

# date –s 15:40:30

Using - -date or –d option for displaying past dates:

· Date and time of 2 years ago.

Command:

$date --date="2 year ago"

Output:

Sat Oct 10 23:42:15 PDT 2019

· Date and time of 5 seconds ago.

Command:

$date --date="5 sec ago"

Output:

Tue Oct 10 23:45:02 PDT 2018

· Date and time of previous day.

Command:

$date --date="yesterday"

Output:

Mon Oct 9 23:48:00 PDT 2018

· Date and time of 2 months ago.

Command:

$date --date="2 month ago"

Output:

Thu Aug 10 23:54:51 PDT 2018

· Date and time of 10 days ago.

Command:

$date --date="10 day ago"

Output:

Sat Sep 30 23:56:55 PDT 2018

Using - -date option for displaying future date:

· Date and time of upcoming particular week day.

Command:

$date --date="next tue"

Output:

Tue Oct 17 00:00:00 PDT 2018

· Date and time after two days.

Command:

$date --date="2 day"

Output:

Fri Oct 13 00:05:52 PDT 2018

· Date and time of next day.

Command:

$date --date="tomorrow"

Output:

Thu Oct 12 00:08:47 PDT 2018

· Date and time after 1 year on the current day.

Command:

$date --date="1 year"

Output:

Thu Oct 11 00:11:38 PDT 2019