centos2ol_wrapper -- Wrapper with sanity checks for centos2ol

The script is downloadable from GitHub as a part of  Softpanorama sysadmin utilities

It incorporates several "no nonsense" checks that make success of the conversion more probable. I experienced around 30% failure rate in my early tests (mostly form rush and inexperience) and 10% of "hard failure" (or one server out of ten failed to report after the conversion was finished). Serious troubles include but not limited to  deletion of hundreds of vital RPMs ( due to my mistake made out  of frustration; but still it is regrettable that there is no protection from this kind  of errors), if safety measures are ignored. So failures due to the lack of pre-conversions checks is not a hypothetic scenario, especially failure on the state of rolling our Oracle RPMs, when the system in "transitional state" and can't be safely rebooted. It is an important safety measure if you convert multiple CentOS or RHEL servers to Oracle Linux and need to convert  important production servers.

The script accepts options -d, -b -p, -r (other than -h which print this help screen and -v for verbose output)

You can also adapt configuration parameters that set defaults for those options

See  Converting CentOS to Oracle Linux with centos2ol script for details

OPTIONS

• -b -- BASE directory -- directory for backup and temp files
• -v -- produces trace of script execution by setting bash -x option
• -r -- change the root password to new value before invoking centos2ol.sh script. If the length of the provided password less than 6, the default password centos2p is used. So -r 1 is equivalent to -r centos2p. This option is important in mass conversions. The situations when the conversion process runs into troubles and you do not know the root password (ssh does not work) are no uncommon
• -p -- proxy. For example -p www-proxy.mycompany.com
• -d -- debug mode
  • 0 -- Production mode in which centos2ol is launched from the wrapper. This is the default.
  • 1 -- Testing mode. Any value above zero blocks execution of centos2ol script and enables automatic saving of the script in the $HOME/Archive directory if the source was changed since the last invocation.
  • 2 -- Same as -d 1 but activates tracing via bash option -x (like option -v does)

PARAMETERS

Only one optional parameter is accepted -- path_to_centos2ol_script -- The fully qualified name of the conversion script (with path).  The default is /root/bin/centos2ol.sh. For example, the invocation

./centos2ol_wrapper -r -d 0 /tmp/centos2ol_plus.sh

will use /tmp location for the script centos2ol_plus.sh (assumed to be a modified version of the original centos2ol.sh script)

NEWS CONTENTS

• 20201230 : Switching from CentOS to Oracle Linux: a hands-on example ( Dec 15, 2020 Simon Coter Blog )
• 20201228 : centos2ol_wrapper ( centos2ol_wrapper, Dec 28, 2020 )

Old News ;-)

[Dec 30, 2020] Switching from CentOS to Oracle Linux: a hands-on example

In view of the such effective and free promotion of Oracle Linux by IBM/Red Hat brass as the top replacement for CentOS, the script can probably be slightly enhanced.

The script works well for simple systems, but still has some sharp edges. Checks for common bottlenecks should be added. For exmple scale in /boot should be checked if this is a separate filesystem. It was not done. See my Also, in case it was invoked the second time after the failure of the step "Installing base packages for Oracle Linux..." it can remove hundreds of system RPM (including sshd, cron, and several other vital packages ;-).

And failures on this step are probably the most common type of failures in conversion. Inexperienced sysadmins or even experienced sysadmins in a hurry often make this blunder running the script the second time.

It probably happens due to the presence of the line 'yum remove -y "${new_releases[@]}" ' in the function remove_repos, because in their excessive zeal to restore the system after error the programmers did not understand that in certain situations those packages that they want to delete via YUM have dependences and a lot of them (line 65 in the current version of the script) Yum blindly deletes over 300 packages including such vital as sshd, cron, etc. Due to this execution of the script probably should be blocked if Oracle repositories are already present. This check is absent.

After this "mass extinction of RPM packages," event you need to be pretty well versed in yum to recover. The names of the deleted packages are in yum log, so you can reinstall them and something it helps. In other cases system remain unbootable and the restore from the backup is the only option.

Due sudden surge of popularity of Oracle Linux due to Red Hat CentOS8 fiasco, the script definitely can benefit from better diagnostics. The current diagnostic is very rudimentary. It might also make sense to make steps modular in the classic /etc/init.d fashion and make initial steps shippable so that the script can be resumed after the error. Most of the steps have few dependencies, which can be resolved by saving variables during the first run and sourcing them if the the first step is not step 1.

Also, it makes sense to check the amount of free space in /boot filesystem if /boot is a separate filesystem. The script requires approx 100MB of free space in this filesystem. Failure to write a new kernel to it due to the lack of free space leads to the situation of "half-baked" installation, which is difficult to recover without senior sysadmin skills.

See additional considerations about how to enhance the script at http://www.softpanorama.org/Commercial_linuxes/Oracle_linux/conversion_of_centos_to_oracle_linux.shtml

Dec 15, 2020 Simon Coter Blog

... ... ...

We published a blog post earlier this week that explains why , but here is the TL;DR version:

• Oracle Linux is free to download, distribute and use (even in production) and has been since its release over 14 years ago
• Installation media, updates and source code are all publicly available on the Oracle Linux yum server with no login or authentication requirements
• Since its first release in 2006, Oracle Linux has been 100% application binary compatible with the equivalent RHEL version. In that time, we have never had a compatibility bug logged.

For these reasons, we created a simple script to allow users to switch from CentOS to Oracle Linux about five years ago. This week, we moved the script to GitHub to allow members of the CentOS community to help us improve and extend the script to cover more CentOS respins and use cases.

The script can switch CentOS Linux 6, 7 or 8 to the equivalent version of Oracle Linux. Let's take a look at just how simple the process is.

Download the centos2ol.sh script from GitHub

The simplest way to get the script is to use curl :

$ curl -O https://raw.githubusercontent.com/oracle/centos2ol/main/centos2ol.sh
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 10747 100 10747 0 0 31241 0 --:--:-- --:--:-- --:--:-- 31241

If you have git installed, you could clone the git repository from GitHub instead.

Run the centos2ol.sh script to switch to Oracle Linux

To switch to Oracle Linux, just run the script as root using sudo :

$ sudo bash centos2ol.sh

Sample output of script run .

As part of the process, the default kernel is switched to the latest release of Oracle's Unbreakable Enterprise Kernel (UEK) to enable extensive performance and scalability improvements to the process scheduler, memory management, file systems, and the networking stack. We also replace the existing CentOS kernel with the equivalent Red Hat Compatible Kernel (RHCK) which may be required by any specific hardware or application that has imposed strict kernel version restrictions.

Switching the default kernel (optional)

Once the switch is complete, but before rebooting, the default kernel can be changed back to the RHCK. First, use grubby to list all installed kernels:

[demo@c8switch ~]$ sudo grubby --info=ALL | grep ^kernel
[sudo] password for demo:
kernel="/boot/vmlinuz-5.4.17-2036.101.2.el8uek.x86_64"
kernel="/boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64"
kernel="/boot/vmlinuz-4.18.0-193.el8.x86_64"
kernel="/boot/vmlinuz-0-rescue-0dbb9b2f3c2744779c72a28071755366"

In the output above, the first entry (index 0) is UEK R6, based on the mainline kernel version 5.4. The second kernel is the updated RHCK (Red Hat Compatible Kernel) installed by the switch process while the third one is the kernel that were installed by CentOS and the final entry is the rescue kernel.

Next, use grubby to verify that UEK is currently the default boot option:

[demo@c8switch ~]$ sudo grubby --default-kernel
/boot/vmlinuz-5.4.17-2036.101.2.el8uek.x86_64

To replace the default kernel, you need to specify either the path to its vmlinuz file or its index. Use grubby to get that information for the replacement:

[demo@c8switch ~]$ sudo grubby --info /boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64
index=1
kernel="/boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64"
args="ro crashkernel=auto resume=/dev/mapper/cl-swap rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet $tuned_params"
root="/dev/mapper/cl-root"
initrd="/boot/initramfs-4.18.0-240.1.1.el8_3.x86_64.img $tuned_initrd"
title="Oracle Linux Server (4.18.0-240.1.1.el8_3.x86_64) 8.3"
id="0dbb9b2f3c2744779c72a28071755366-4.18.0-240.1.1.el8_3.x86_64"

Finally, use grubby to change the default kernel, either by providing the vmlinuz path:

[demo@c8switch ~]$ sudo grubby --set-default /boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64
The default is /boot/loader/entries/0dbb9b2f3c2744779c72a28071755366-4.18.0-240.1.1.el8_3.x86_64.conf with index 1 and kernel /boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64

Or its index:

[demo@c8switch ~]$ sudo grubby --set-default-index 1
The default is /boot/loader/entries/0dbb9b2f3c2744779c72a28071755366-4.18.0-240.1.1.el8_3.x86_64.conf with index 1 and kernel /boot/vmlinuz-4.18.0-240.1.1.el8_3.x86_64

Changing the default kernel can be done at any time, so we encourage you to take UEK for a spin before switching back.

It's easy to access, try it out.

• Switch from CentOS to Oracle Linux
• Installation media and updates freely available from the Oracle Linux yum server .
• UEK source code on GitHub

For more information visit oracle.com/linux .

[Dec 28, 2020] centos2ol_wrapper Wrapper with sanity checks for centos2ol.

It incorporates several "no nonsense" checks that make success of the conversion more probable. I experienced around 30% failure rate iin my tests and 10% (or one server out of ten failed to report after the conversion was finished). Serious troubles include but not limited to deletion of hundreds of vital RPMs ( due to my mistake made out of frustration; nit stll no protection from this kind of errors), if safety measures are ignored. So failures due to the lack of pre-conversions checks is not a hypothetic scenario, especially failure on the state of rolling our Oracle RPMs, when the system in "transitional state" and can't be safely rebooted. It is an important safety measure if you convert multiple CentOS or RHEL servers to Oracle Linux and need to convert important production servers. Man page at centos2ol_wrapper. See Converting CentOS to Oracle Linux with centos2ol script for details

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Last modified: January 02, 2021