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Switch to a new master (primary) in MySQL InnoDB Cluster 8

Switching to a new master (or new primary if to use the new naming) in a MySQL 8 InnoDB Cluster is simple with the MySQL Shell console and the function of the cluster variable – setPrimaryInstance.

main menu — MySQL Shell with setPrimaryInstance

Why would someone need to do it manually? One of the reasons may be because one of the nodes is on the same physical server and thus suppose a smaller latency.

First, get a cluster object of the cluster by connecting to the cluster API with MySQL Shell:

[root@db-cluster-1 ~]# mysqlsh
MySQL Shell 8.0.28

Copyright (c) 2016, 2022, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its affiliates.
Other names may be trademarks of their respective owners.

Type '\help' or '\?' for help; '\quit' to exit.
 MySQL  JS > \connect clusteradmin@db-cluster-1
Creating a session to 'clusteradmin@db-cluster-1'
Fetching schema names for autocompletion... Press ^C to stop.
Your MySQL connection id is 166928419 (X protocol)
Server version: 8.0.28 MySQL Community Server - GPL
No default schema selected; type \use <schema> to set one.
 MySQL  db-cluster-1:33060+ ssl  JS > var cluster = dba.getCluster()

Second, show the status of the cluster to get the cluster topology and the exact nodes’ names, which will use as an argument of the setPrimaryInstance. Still, in the MySQL Shell Console:

 MySQL  db-cluster-1:33060+ ssl  JS > cluster.status()
{
    "clusterName": "mycluster1", 
    "defaultReplicaSet": {
        "name": "default", 
        "primary": "db-cluster-2:3306", 
        "ssl": "REQUIRED", 
        "status": "OK", 
        "statusText": "Cluster is ONLINE and can tolerate up to ONE failure.", 
        "topology": {
            "db-cluster-1:3306": {
                "address": "db-cluster-1:3306", 
                "memberRole": "SECONDARY", 
                "mode": "R/O", 
                "readReplicas": {}, 
                "replicationLag": null, 
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.28"
            }, 
            "db-cluster-2:3306": {
                "address": "db-cluster-2:3306", 
                "memberRole": "PRIMARY", 
                "mode": "R/W", 
                "readReplicas": {}, 
                "replicationLag": null, 
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.28"
            }, 
            "db-cluster-3:3306": {
                "address": "db-cluster-3:3306", 
                "memberRole": "SECONDARY", 
                "mode": "R/O", 
                "readReplicas": {}, 
                "replicationLag": null, 
                "role": "HA", 
                "status": "ONLINE", 
                "version": "8.0.28"
            }
        }, 
        "topologyMode": "Single-Primary"
    }, 
    "groupInformationSourceMember": "db-cluster-2:3306"
}

Keep on reading!

Install CentOS Stream 9 booting VNC installer with kexec

Lately, dedicated servers come with Remote management consoles like IPMI KVM or iLO, or DRAC, but they are still slow to initiate the process of installing a system.

Consider a server (dedicated or not) should be installed in a remote colocation with the help of only the server’s network. The system administrator just receives an administrative shell access and nothing more and the server should be installed with the proper and secured software, in this case, the CentOS Stream 9. Using kexec the user can boot a new kernel from a different Linux Distribution and initiate automated network installation of the system and it is not needed any Remote management consoles. The only thing needed is the ability of the current system/kernel to be able to use kexec, which is pretty standard for 8 to 10 years old Linux systems. There is a good chance the colocations’ rescue CD/DVD/USB flash drives or the PXE rescue images support kexec, because they tend to upgrade their rescue systems, which the user may boot if he has problems.
Still, using kexec to initiate another kernel or Linux Distribution like CentOS Stream 9 with VNC installer, for example, it a powerful tool to safely replace a currently running system with only shell access.
This article has chosen to start the CentOS Stream 9 VNC installer just for demonstration purposes. Booting a downloaded kernel may be used for just anything from booting a system over the network, booting an installer, booting an unattended automation installation, and so on. There are a couple of simple things to check before booting the new kernel.
This article will show just one use case – reinstalling a system with CentOS Stream 9 over the network using the CentOS VNC Install. The purpose is to show how simple, fast, and easy is to install a modern Linux system only by having console access. No scripts are required if manual installation is performed.
To boot a CentOS Stream 9 VNC Installer the kexec command needs the following options.

The kexec commands need the following options:

Networking – device interface name, IP, netmask, gateway and DNS servers
Kernel options – these options will initiate scripts from the initramfs.
inst.vnc – a kernel option, which will start a VNC server with no password on the default port and network device. Using it with another inst.vncpassword=[PASSWORD] the VNC server will require the password – [PASSWORD]. The password should be a maximum of 8 characters because the VNC server will not start if it is with more!
inst.repo=[HTTP/HTTPS://repository] – a kernel option, which sets the CentOS HTTP/HTTPS repository.

The kexec command to boot the CentOS Stream 9 VNC Installer is:

kexec --initrd=./initrd.img -l ./vmlinuz --command-line="bootdev=eno1 ip=10.10.10.20::10.10.10.1:24:srv.example.com:eno1:none nameserver=8.8.8.8 inst.vnc inst.vncpassword=cha3hae4ahZaqueev1ee inst.repo=https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/"

The kernel (i.e. vmlinuz) and the initramfs (i.e. initrd.img) should be downloaded in the current directory before executing the above command. The above line will order the kernel to load the new kernel, but to boot it another command must be executed:

kexec -e

Keep on reading!

Run a docker container with bigger storage

By default, the Docker command-line utility docker runs containers with 10G storage, which in most cases is enough, but if the user wants to just run a specific container with bigger storage there is an option for the docker command:

docker run --storage-opt size=50G

The option size=50G will set the docker container storage for the current only run command!

Run a Ubuntu 22.04 Docker container with 50G root storage:

root@srv ~ # docker run --storage-opt size=50G -it ubuntu:22.04 bash
Unable to find image 'ubuntu:22.04' locally
22.04: Pulling from library/ubuntu
e96e057aae67: Pull complete 
Digest: sha256:4b1d0c4a2d2aaf63b37111f34eb9fa89fa1bf53dd6e4ca954d47caebca4005c2
Status: Downloaded newer image for ubuntu:22.04
root@4caab8c61157:/# df -h
Filesystem                                                                                          Size  Used Avail Use% Mounted on
/dev/mapper/docker-253:0-39459726-2f2d655687e5bd39620a2a083960ac969d8163b806152765a1fc166f0a82d3d9   50G  170M   50G   1% /
tmpfs                                                                                                64M     0   64M   0% /dev
tmpfs                                                                                               7.8G     0  7.8G   0% /sys/fs/cgroup
shm                                                                                                  64M     0   64M   0% /dev/shm
/dev/mapper/map-99f55d81-4132-42d4-9515-33d8cc11d3e2                                                3.6T  1.5T  2.2T  40% /etc/hosts
tmpfs                                                                                               7.8G     0  7.8G   0% /proc/asound
tmpfs                                                                                               7.8G     0  7.8G   0% /proc/acpi
tmpfs                                                                                               7.8G     0  7.8G   0% /proc/scsi
tmpfs

It’s worth mentioning this option “–storage-opt size=50G” is different from the “–storage-opt dm.basesize=50G“, the first one is used as a command argument to the docker command-line utility. The second one is used with the dockerd daemon to change the default Docker behavior from 10G to 50G storage. Note, either option cannot change the storage size of the already started container.

Migrate emails from GMail to another IMAP server with imapsync

It appears pretty easy to migrate an existing GMail account to another IMAP server, i.e. not GMail/Google server. There is an excellent synchronization tool – imapsync, which checks and downloads all the mails of an user account from one IMAP server to another IMAP server per user. The tool supports Google’s GMail accounts and their specific naming including the labels folders peculiarity (some folders in GMail may not have any physical emails, but just to show emails from another folders with specific labels). It’s worth mentioning that the imapsync works only only with GMail accounts, but it can be used to migrate from one IMAP server to another IMAP. The key here is the source and the destination server should support IMAP protocol.

Imapsync is an IMAP transfer tool. The purpose of imapsync is to migrate IMAP accounts or to backup IMAP accounts.

GMail will expose the labels as folders and in some early versions of the imapsync tool the emails with multiple labels may be shown in multiple folders and be duplicated. The version used here did not duplicate any email, even some emails were shown in multiple GMail folders.

There are two GMail settings to enable before proceeding with the migration:

Enable “Less secure app access” or if 2-Step-Verification is enabled use App Passwords
Enable IMAP, which is disabled by default.

SCREENSHOT 1) Manage the current Google account options by clicking on the top right corner as shown in the screenshot.

Keep on reading!

git status and bus error on SSD – fix READ errors by recovering part of the file

SSD and Linux encryption may not be the best idea, especially without the TRIM (allow-discards) option (or never executed fstrim?). Nevertheless, this error may occur not only on an SSD device, but just where there is a corrupted file system or device.
In our case, the SSD has some read errors. Apparently, some files or some parts of files could not be read by the git command:

[myuser@dekstop kernel]# git status -v
Bus error 84/115708)

In the case of SSD bad reads, the only working solution is to find and overwrite the problem file(s) or remove the file(s) and recreate them. A more sophisticated solution is to dump the file with dd and skip errors option enabled to another location and then overwrite the old file with the new one. So only the corrupted area of the file will be lost, which in most cases is just one or two sectors, i.e. one or two 512 bytes of data.

STEP 1) Find the bad files with the find command.

Use find Linux command and read all the files with the cat Linux command, so a bad sector will output an input/output error on READ. On write errors won’t be generated, but the sector will be automatically moved to a healthy one (the bad sector is marked and never used more).

[myuser@dekstop kernel]#  find -type f -exec cat {} > /dev/null \;
cat: ./servers/logo_description.txt: Input/output error

If multiple files are found repeat the procedure with each file.

STEP 2) Copy the healthy portion of the file.

The easiest way to remove the error is just to delete the file (or overwrite it), but if the healthy portion of the file is desirable the dd utility may be used to recover it:
Keep on reading!

Show deleted partitions in use with blockdev –report

blockdev Linux command could show sector and size information for deleted partitions, which are still in use (i.e. mounted).
Deleting partitions in use their characters’ devices under /dev are preserved till the partitions are released from use and the kernel reloads the new partition table.
So before rebooting or releasing the deleted partitions blockdev may be used to report useful information for future recovery:

Delete the partitions with parted by just overwriting the partition table with empty one, for example:

[root@srv ~]# parted /dev/sda
GNU Parted 3.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: ATA Crucial_CT500MX2 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
 1      1049kB  34.3GB  34.3GB  primary                boot, raid
 2      34.4GB  34.9GB  537MB   primary                raid
 3      34.9GB  67.1GB  32.2GB  primary                raid
 4      67.1GB  500GB   433GB   extended               lba
 5      67.1GB  500GB   433GB   logical                raid
(parted) mklabel msdos
Warning: The existing disk label on /dev/sda will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? Yes
Error: Partition(s) 1, 2, 3, 4, 5 on /dev/sda have been written, but we have been unable to inform the kernel of the change, probably because
it/they are in use.  As a result, the old partition(s) will remain in use.  You should reboot now before making further changes.
Ignore/Cancel? Cancel
(parted) p
Model: ATA Crucial_CT500MX2 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags: 

Number  Start  End  Size  Type  File system  Flags

(parted) q

First, print the partition table, then delete all partitions by setting an empty new partition table!

Use blockdev to show the deleted partitions information.

[root@srv ~]# blockdev --report /dev/sda1 /dev/sda2 /dev/sda3 /dev/sda4 /dev/sdb5
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw   512   512  4096       2048     34359738368   /dev/sda1
rw   512   512  4096   67110912       536870912   /dev/sda2
rw   512   512  4096   68159488     32212254720   /dev/sda3
blockdev: cannot open /dev/sda4: No such file or directory.
rw   256   512  4096  131076096    432862658560   /dev/sdb5

The partitions, which are not in use, are removed from the kernel structures, so no information is available with blockdev. Their characters’ devices under /dev/ are removed, too.

The information such as the size of the partitions and the start sectors may be used to recover the partitions manually with fdisk, sfdisk, sgdisk or parted or even testdisk – testdisk official site. In fact, testdisk is the recommended way.

Copying partition table from one disk to another with older sfdisk under CentOS 7

Older version of sfdisk may still be used for msdos partition tables.
To copy the partition table from one disk to another using sfdisk a temporary file should be used to store the data for the partition table.

Here is an example of how to copy the msdos partition table from disk sda to disk sdb! Two simple commands

Dump the source (sda) partition table to a temporary file.
Redirect the standard input of the sfdisk utility with the above temporary file.

A copying partition table is really useful when recovering from a drive failure in a Linux software raid. Sometimes it is difficult or just easier to create the exact layout as the source mirror disk!

mdadm --add /dev/md1 /dev/sdb2
mdadm: /dev/sdb2 not large enough to join array

Errors such as the above are easily resolved with just two commands. The new versions of disk programs align the partitions, which may be a problem for a software RAID to join in a partition.

STEP 1) Dump the source partition table.

The source partition table is from /dev/sda:

[root@srv ~]# sfdisk -d /dev/sda > part_table_sda
sfdisk: Warning: extended partition does not start at a cylinder boundary.
DOS and Linux will interpret the contents differently.

There is a warning about not aligned partition, which may cause problems when creating from scratch, so copying the partition table is the best option in such cases.

Here is what the temporary file part_table_sda with the partition table information contains:

[root@srv ~]# cat part_table_sda 
# partition table of /dev/sda
unit: sectors

/dev/sda1 : start=     2048, size= 67045376, Id=fd, bootable
/dev/sda2 : start= 67110912, size=  1048576, Id=fd
/dev/sda3 : start= 68159488, size= 62883840, Id=fd
/dev/sda4 : start=131043328, size=845729792, Id= f
/dev/sda5 : start=131076096, size=845434880, Id=fd

Keep on reading!

rsync server under CentOS 8 with SELinux enabled

Here is a quick and useful tip on how to run a rsync daemon under CentOS 8 with SELinux in Enforcing mode.
There are three basic steps:

rsync daemon installation and configuration.
firewall configuration.
SELinux configuration.

STEP 1) rsync daemon installation and configuration.

Under CentOS 8 rsync daemon files are in a separate rpm package rsync-daemon (more on the subject rsync daemon in CentOS 8):

[root@srv ~]# dnf install -y rsync-daemon
Last metadata expiration check: 2:45:48 ago on Thu Apr  7 07:40:42 2022.
Dependencies resolved.
==============================================================================================================
 Package                     Architecture          Version                        Repository             Size
==============================================================================================================
Installing:
 rsync-daemon                noarch                3.1.3-14.el8                   baseos                 43 k

Transaction Summary
==============================================================================================================
Install  1 Package

Total download size: 43 k
Installed size: 17 k
Downloading Packages:
rsync-daemon-3.1.3-14.el8.noarch.rpm                                           98 kB/s |  43 kB     00:00    
--------------------------------------------------------------------------------------------------------------
Total                                                                          81 kB/s |  43 kB     00:00     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                                                      1/1 
  Installing       : rsync-daemon-3.1.3-14.el8.noarch                                                     1/1 
  Running scriptlet: rsync-daemon-3.1.3-14.el8.noarch                                                     1/1 
  Verifying        : rsync-daemon-3.1.3-14.el8.noarch                                                     1/1 

Installed:
  rsync-daemon-3.1.3-14.el8.noarch                                                                            

Complete!

Keep on reading!

Change found sources for kernel version when packages need the kernel sources to compile

Multiple Gentoo packages may need kernel sources to compile. There are packages, which are external modules such as virtualbox-modules or video drivers or wifi drivers or more. All these packages expect the current loaded kernel sources are present and to use them when compiling the external kernel module. But sometimes the proper kernel sources are missing, those needed to compile the kernel module in such a way to load it in the currently loaded kernel.

This article is valid not only for Gentoo Linux distribution but any Linux and kernel sources. So, if the user needs to have properly configured kernel sources for the currently loaded kernel, this is one way to do it right.

Here is an example: Updated kernel, but no sources are kept and then the VirtualBox needs to update to a newer version, but with the missing kernel sources of the currently loaded kernel updating the VirtualBox will cause the VirtualBox to stop working!

root@srv ~ # uname -a
Linux srv 5.15.5-gentoo #2 SMP Tue Nov 30 16:08:49 EET 2021 x86_64 Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz GenuineIntel GNU/Linux
root@srv ~ # emerge -va app-emulation/virtualbox-modules

These are the packages that would be merged, in order:

[ebuild     U  ] app-emulation/virtualbox-modules-6.1.32:0/6.1::gentoo [6.1.26:0/6.1::gentoo] USE="dist-kernel -pax-kernel" 660 KiB

Total: 1 packages (1 upgrades), Size of downloads: 0 KiB

Would you like to merge these packages? [Yes/No] yes

>>> Verifying ebuild manifests

>>> Running pre-merge checks for app-emulation/virtualbox-6.1.32-r1

>>> Emerging (1 of 1) app-emulation/virtualbox-modules-6.1.32::gentoo
 * Fetching files in the background.
 * To view fetch progress, run in another terminal:
 * tail -f /var/log/emerge-fetch.log
 * vbox-kernel-module-src-6.1.32.tar.xz BLAKE2B SHA512 size ;-) ...                                                                                                                   [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     5.14.2-gentoo-x86_64-genkernel-NEW2
 * Checking for suitable kernel configuration options...                                                                                                                              [ ok ]
>>> Unpacking source...
>>> Unpacking vbox-kernel-module-src-6.1.32.tar.xz to /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work
>>> Source unpacked in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work
>>> Preparing source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...
>>> Source prepared.
>>> Configuring source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...
>>> Source configured.
>>> Compiling source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...

Here is the problem: the currently loaded kernel is version 5.15.5-gentoo and the emerge system finds only sources for 5.14.2-gentoo-x86_64-genkernel-NEW2, which will use to produce modules for the 5.14.2-gentoo-x86_64-genkernel-NEW2. It is obvious enough the modules compiled against kernel sources of 5.14.2-gentoo-x86_64-genkernel-NEW2 version won’t be possible to be loaded under the currently load kernel with version 5.15.5-gentoo.
Here is how to fix this:

Get the kernel sources for 5.15.5-gentoo in /usr/src/linux
Save the currently loaded kernel config in /usr/src/linux/.config
Load the configuration and prepare the kernel sources. No need to compile the kernel sources.

STEP 1) Get the kernel sources for 5.15.5-gentoo

emerge -v =gentoo-sources-5.15.5
rm -f /usr/src/linux
ln -s /usr/src/linux-5.15.5-gentoo /usr/src/linux

These commands will install the needed kernel version and a link to the kernel sources will be created.
Of course, change the kernel version to the proper version if needed.

STEP 2) Save the currently loaded kernel config in /usr/src/linux/.config

zcat /proc/config.gz > /usr/src/linux/.config

If the /proc/config.gz is missing, copy the configuration from the /boot for the currently loaded kernel:

cat /boot/config-5.15.5-gentoo > /usr/src/linux-5.15.5-gentoo/.config

STEP 3) Load the configuration and prepare the kernel sources.

No need to compile the whole kernel source tree. Just to commands to configure and prepare the kernel sources:

cd /usr/src/linux-5.15.5-gentoo
make oldconfig
make prepare

The commands take Here is the output of the last commands:

root@srv1 ~ # cd /usr/src/linux-5.15.5-gentoo
root@srv1 linux # make oldconfig
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  HOSTCC  scripts/kconfig/lexer.lex.o
  HOSTCC  scripts/kconfig/menu.o
  HOSTCC  scripts/kconfig/parser.tab.o
  HOSTCC  scripts/kconfig/preprocess.o
  HOSTCC  scripts/kconfig/symbol.o
  HOSTCC  scripts/kconfig/util.o
  HOSTLD  scripts/kconfig/conf
#
# configuration written to .config
#
root@srv1 linux # make prepare
  SYNC    include/config/auto.conf.cmd
  HOSTCC  arch/x86/tools/relocs_32.o
  HOSTCC  arch/x86/tools/relocs_64.o
  HOSTCC  arch/x86/tools/relocs_common.o
  HOSTLD  arch/x86/tools/relocs
  HOSTCC  scripts/selinux/genheaders/genheaders
  HOSTCC  scripts/selinux/mdp/mdp
  HOSTCC  scripts/bin2c
  HOSTCC  scripts/kallsyms
  HOSTCC  scripts/sorttable
  HOSTCC  scripts/asn1_compiler
  HOSTCC  scripts/extract-cert
  UPD     include/config/kernel.release
  UPD     include/generated/utsrelease.h
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  CC      scripts/mod/devicetable-offsets.s
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  UPD     include/generated/bounds.h
  CC      arch/x86/kernel/asm-offsets.s
  UPD     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND objtool
  HOSTCC  /usr/src/linux-5.15.5-gentoo/tools/objtool/fixdep.o
  HOSTLD  /usr/src/linux-5.15.5-gentoo/tools/objtool/fixdep-in.o
  LINK    /usr/src/linux-5.15.5-gentoo/tools/objtool/fixdep
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/exec-cmd.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/help.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/pager.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/parse-options.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/run-command.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/sigchain.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/subcmd-config.o
  LD      /usr/src/linux-5.15.5-gentoo/tools/objtool/libsubcmd-in.o
  AR      /usr/src/linux-5.15.5-gentoo/tools/objtool/libsubcmd.a
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/arch/x86/special.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/arch/x86/decode.o
  LD      /usr/src/linux-5.15.5-gentoo/tools/objtool/arch/x86/objtool-in.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/weak.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/check.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/special.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/orc_gen.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/orc_dump.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/builtin-check.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/builtin-orc.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/elf.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/objtool.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/libstring.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/libctype.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/str_error_r.o
  CC      /usr/src/linux-5.15.5-gentoo/tools/objtool/librbtree.o
  LD      /usr/src/linux-5.15.5-gentoo/tools/objtool/objtool-in.o
  LINK    /usr/src/linux-5.15.5-gentoo/tools/objtool/objtool

And from now on whenever the kernel sources are needed to compile modules or libraries against, the proper kernel sources will be used of the currently loaded kernel.
The Gentoo emerge command from the begging of this article, but this time with the properly configured kernel sources. The VirtualBox modules are compiled against the loaded kernel, so loading them is not an issue anymore!

root@srv ~ # uname -a
Linux srv 5.15.5-gentoo #2 SMP Tue Nov 30 16:08:49 EET 2021 x86_64 Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz GenuineIntel GNU/Linux
root@srv ~ # emerge -va app-emulation/virtualbox-modules

These are the packages that would be merged, in order:

[ebuild     U  ] app-emulation/virtualbox-modules-6.1.32:0/6.1::gentoo [6.1.26:0/6.1::gentoo] USE="dist-kernel -pax-kernel" 660 KiB

Total: 1 packages (1 upgrades), Size of downloads: 0 KiB

Would you like to merge these packages? [Yes/No] yes

>>> Verifying ebuild manifests

>>> Running pre-merge checks for app-emulation/virtualbox-6.1.32-r1

>>> Emerging (1 of 1) app-emulation/virtualbox-modules-6.1.32::gentoo
 * Fetching files in the background.
 * To view fetch progress, run in another terminal:
 * tail -f /var/log/emerge-fetch.log
 * vbox-kernel-module-src-6.1.32.tar.xz BLAKE2B SHA512 size ;-) ...                                                                                                                   [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     5.15.5-gentoo-gentoo
 * Checking for suitable kernel configuration options...                                                                                                                              [ ok ]
>>> Unpacking source...
>>> Unpacking vbox-kernel-module-src-6.1.32.tar.xz to /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work
>>> Source unpacked in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work
>>> Preparing source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...
>>> Source prepared.
>>> Configuring source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...
>>> Source configured.
>>> Compiling source in /var/tmp/portage/app-emulation/virtualbox-modules-6.1.32/work ...
....
....
root@srv ~ # modprobe vboxdrv
Feb 15 14:15:10 www kernel: vboxdrv: loading out-of-tree module taints kernel.
Feb 15 14:15:10 www kernel: vboxdrv: Found 4 processor cores
Feb 15 14:15:10 www kernel: vboxdrv: TSC mode is Invariant, tentative frequency 2394461773 Hz
Feb 15 14:15:10 www kernel: vboxdrv: Successfully loaded version 6.1.32 r149290 (interface 0x00320000)
Feb 15 14:15:10 www kernel: VBoxNetFlt: Successfully started.

CentOS 8.2 (RHEL 8.2) and above including CentOS Stream 9

SCREENSHOT 1) Manage the current Google account options by clicking on the top right corner as shown in the screenshot.

STEP 1) Find the bad files with the find command.

STEP 2) Copy the healthy portion of the file.

Use blockdev to show the deleted partitions information.

STEP 1) Dump the source partition table.

STEP 1) rsync daemon installation and configuration.

STEP 1) Get the kernel sources for 5.15.5-gentoo

STEP 2) Save the currently loaded kernel config in /usr/src/linux/.config

STEP 3) Load the configuration and prepare the kernel sources.