VBoxManage: error: Failed to initialize COM! NS_ERROR_FILE_TARGET_DOES_NOT_EXIST (0x80520006)

What an error! And the VirtualBox stopped loading anymore! This error:

myuser@srv ~ $ VBoxManage list vms
VBoxManage: error: Failed to initialize COM! (hrc=NS_ERROR_FILE_TARGET_DOES_NOT_EXIST)

and here with the GIU, which offers a little bit more information about the error ID:
This error occurs despite the successfully loaded VirtualBox kernel modules!

main menu
VBoxManage: error: Failed to initialize COM! NS_ERROR_FILE_TARGET_DOES_NOT_EXIST (0x80520006)

The two errors are the same and hint there is a file missing (or files?)? In our case, after upgrading from virtualbox-bin (a binary package) to a virtualbox (a package, which actually builds the VirtualBox on the system) under Gentoo, but apparently, this error could occur to everyone, who tries to build yourself the VirtualBox bundle.

The solution is simple: just DO NOT CHANGE the installation path of the Virtualbox software, which by default is /opt/VirtualBox.

The path is hardcoded in the sources and cannot be changed! At present version 6.1.16, we could not find a build option to change it! Of course, the linking /opt/VirtualBox would do the trick to move the installation physically away from the /opt, but the path must be valid /opt/VirtualBox.

In Gentoo, the emerge default installation goes to “/usr/lib64/virtualbox“, so the maintainer of the package changed the path and Virtualbox stopped working! Or a user build it and install it in any other location should link the /opt/VirtualBox to the installation directory. For example, in Gentoo, the fix will be:

root@srv ~ $ ln -s /usr/lib64/virtualbox /opt/VirtualBox
root@srv ~ $ exit
myuser@srv ~ $ VBoxManage list vms
"gentoo_raw" {55346caf-04db-4d88-831a-111111111111}
"diskless" {44346caf-c952-5555-b8a3-111111111111}
"diskless-linux" {44346caf-424f-487f-ae8d-111111111111}
"centos7-netinstall" {44346caf-4e86-441b-8d1e-111111111111}

A simple link would bring back Virtualbox to live.


Probably, there is a configuration file “xpti.dat” in two or more locations: ~/.config/VirtualBox/xpti.dat and ~/.VirtualBox/xpti.dat, which is generated on every start of a VirtualBox. In the file there are configuration lines like:
Keep on reading!

removing the default kernel in CentOS 8 – remove elrepo kernel

Removing the default kernel aka the loaded kernel in CentOS 8 maybe challenging because the package is protected and cannot be removed by the yum or dnf.
Here is the case: an elrepo kernel-ml loaded and the dnf prints it cannot remove the package, because it is protected:

[root@srv ~]# dnf remove kernel-ml kernel-ml-core kernel-ml-modules
 Problem: The operation would result in removing the following protected packages: kernel-ml-core
(try to add '--skip-broken' to skip uninstallable packages or '--nobest' to use not only best candidate packages)
[root@srv ~]# uname -a
Linux srv.localhost 5.10.4-1.el8.elrepo.x86_64 #1 SMP Tue Dec 29 11:04:23 EST 2020 x86_64 x86_64 x86_64 GNU/Linux
[root@srv ~]# grubby --default-kernel

The system is booted up with the kernel we are trying to remove, which is impossible.

The solution is to set a new default kernel and load it. Then dnf will be able to remove the first kernel.

For CentOS 7, just use the yum instead of dnf command.
Using grubby is really easy and straightforward:

STEP 1) List all installed and available to boot kernels

[root@srv ~]# grubby --info=ALL |grep ^kernel

STEP 2) Select the kernel to load the next time

[root@srv ~]# grubby --set-default "/boot/vmlinuz-4.18.0-259.el8.x86_64"
The default is /boot/loader/entries/45e12f0814fd4947b99cbdcb88950361-4.18.0-259.el8.x86_64.conf with index 1 and kernel /boot/vmlinuz-4.18.0-259.el8.x86_64

Keep on reading!

Gentoo emerge GO lang failed – atomic_amd64x.go: too many errors

Upgrading GO lang under Gentoo maybe a little bit tricky. The upgrading go lang from 1.13.7 to 1.15.5 failed with strange error:

# runtime/internal/atomic
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:18:6: Load redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:16:24
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:24:6: Loadp redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:22:32
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:30:6: Load64 redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:28:26
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:36:6: LoadAcq redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:34:27
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:41:6: Xadd redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:39:37
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:44:6: Xadd64 redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:42:39
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:47:6: Xadduintptr redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:45:47
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:50:6: Xchg redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:48:36
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:53:6: Xchg64 redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:51:38
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:56:6: Xchguintptr redeclared in this block
        previous declaration at /usr/lib/go/src/runtime/internal/atomic/atomic_amd64.go:54:45
/usr/lib/go/src/runtime/internal/atomic/atomic_amd64x.go:56:6: too many errors

Googling a little bit and it appeared there might be a conflict with the old version in the same directory. Deleting the temporary build directory didn’t help…

Removing the GO lang package by unmerge command and then emerging the newest GO lang package is successful.

So the solution is to unmerge it and then immediately emerge the newest version with:

emerge -vC dev-lang/go
emerge -v dev-lang/go

The whole Gentoo output of the failed emerge command

Keep on reading!

Booting network installation from ipxe disk using IPMI KVM

There is a project for extended PXE Boot features https://ipxe.org/. This article is not for describing what this project may offer, but to show how to boot any Linux distribution (in fact, Windows 10, too) network installation wizard using the virtual CD/DVD of an IPMI KVM, DELL’s DRAC, HP iLO, IBM RSA/IMM and in general, KVM over IP.
Using the iPXE CD bootable disk mounted in the virtual CD/DVD of the server’s remote console (IPMI KVM and so on) will allow:

  • Booting from a CD/DVD with only a 1M size.
  • Extends the PXE features of the server’s network card.
  • Manual set IP address, i.e. not relying on DHCP server. In addition of the DHCP feature, but DHCP feature requires DHCP server, which is not always the case.
  • Load a Linux kernel and initramfs from a URL.
  • Boot a Linux live or installation CD/DVD from an URL. The server could load the instllation wizard from an official mirror in the Internet.
  • Manual install – boot from 1M CD and continue with multi gigabyte installation from an URL. For comparision the CentOS 8 network installation disk is more than 600M versus 1M iPXE CD disk. Booting directly from a 600M CentOS 8 network installation disk is unstable and really slow when the disk is mounted in user’s KVM. And not alwyas is possible to mount a disk next to the server location (or in the same co-location).
  • Automated install – simple unattended installation with kickstart files without the need of speacial features of the dedicated service provider.
  • No software installation or code writting needed.

This article uses the iPXE CD to boot and manually set an IP and then load the Linux kernel and initramfs of the CentOS 8 installation disk using an official URL mirror on the Internet. All types of server’s KVM, which supports CD/DVD virtual device, can be used.

Just 1 Mbytes of CD/DVD is required to boot an installation of a (connected to the Internet) server/machine.

Here are the steps and correct (all lines are tested) command lines to boot an installation wizard. The server is a SUPERMICRO server with IPMI KVM for remote management.
The iPXE ISO file is located here http://boot.ipxe.org/ipxe.iso

SCREENSHOT 1) Open the IPMI KVM and click on “Virtual Storage” menu to open the image mount dialog.

main menu
Virtual Storage menu

Keep on reading!

gentoo network interface with hyphen in the name

Using the OpenRC (i.e. init system) and network names with special symbols like hyphen in the name may lead to errors of “command not found” and “No such file or directory

The hyphen in the network interface name must be replaced in the configuration file with an underline and the init name file should be with the hyphen.

Proper configuration for network interface name with hyphen mv-eth0

  • In the configuration file /etc/conf.d/net:
    default via
  • The network interface init file is with hyphen:
    root@srv /etc/init.d # ln -s net.lo net.mv-eth0

And starting the network is successful:

root@srv ~ # /etc/init.d/net.mv-eth0 start
 * Caching service dependencies ...                                                                                                                                                     [ ok ]
 * Bringing up interface mv-eth0
 *   Caching network module dependencies
 * ...                                                                                                                                                               [ ok ]
 *   Adding routes
 *     default via ...                                                                                                                                                      [ ok ]
 *   Waiting for tentative IPv6 addresses to complete DAD (5 seconds) ..

Virtualization software may include to the network interface name not so typical alphabets. For example, systemd-nspawn will give name to the guest’s macvlan network with mv-{host_network_name} and iv-{host_network_name} for ipvlan.

Wrong configuration with a hyphen in the network interface name.

The configuration file /etc/conf.d/net:

default via

Starting the network with such configuration will result in multiple errors:

root@srv ~ # /etc/init.d # /etc/init.d/net.mv-eth0 start
 * Caching service dependencies ...
/etc/init.d/../conf.d/net: line 3: config_mv-eth0=
: No such file or directory
/etc/init.d/../conf.d/net: line 6: $'routes_mv-eth0=\ndefault via\n': command not found
/etc/init.d/../conf.d/net: line 3: config_mv-eth0=
: No such file or directory
/etc/init.d/../conf.d/net: line 6: $'routes_mv-eth0=\ndefault via\n': command not found                                                                                  [ ok ]
/etc/init.d/../conf.d/net: line 3: config_mv-eth0=
: No such file or directory
/etc/init.d/../conf.d/net: line 6: $'routes_mv-eth0=\ndefault via\n': command not found
 * net.mv-eth0: error loading /etc/init.d/../conf.d/net
 * ERROR: net.mv-eth0 failed to start

xdg and autostart in Linux X server regardless the desktop environment

There is a tool xdg, which manages application integration with the different GUI Desktops in the Linux world. One of the features it offers is to autostart an application when the X window system starts and it is perfectly normal to have a bunch of running programs that cannot be found in the Windowing manager settings like KDE System Settings -> Autostart, GNOME Tweak tool and Autostart and so on.

xdg offers autostart of Linux appilcations mainly Desktop when the GUI windowing system starts

There two main paths to look for entries to autostart:

  1. /etc/xdg/autostart – called system-wide and most of the application will place files when they are installed.
  2. [user’s home]/.config/autostart – user’s applications to start when the user logs in .

With xdg autostart feature the user can explain himself why the Windowing systems like KDE or GNOME start tens of applications (not exactly related to the base GUI windowing system).

There is a security problem here, which is sometimes installing a package will place an autostart file there because the maintainer decided it is important but the package might be just a dependency and the next time the user logs in unwanted program might execute and open ports!

For example, Rygel is an open-source UPnP/DLNA MediaServer and it might be installed as a dependency but it places an autostart file, which starts a UPnP/DLNA server and exports the /home/[user’s directory]/Videos, /home/[user’s directory]/Pictures and more to the local network. Another example is with the GNOME index system tracker and the tracker-store, which may easily eat the RAM, disk, CPU, battery on a system without GNOME but with a different GUI!

Here is what a typical Ubuntu 18.04 system might autostart

Keep on reading!

starting Hashicorp vault in server mode under docker container

Running Hashicorp vault in development mode is really easy, but starting the vault in server mode under a docker container may have some changes described in this article.

There are several simple steps, which is hard to get in one place, to run a Hashicorp vault in server mode (under docker):

  1. Prepare the directories to map in the docker. The data in the directories will be safe and won’t be deleted if the container is deleted.
  2. Prepare an initial base configuration to start the server. Without it, the server won’t startup. Even it is really simple.
  3. Start the Hashicorp vault process in a docker container.
  4. Initiliza the vault. During this step, the server will generate the database backend storage (files or in-memory or cloud backends) and 5 unseal keys and an administrative root token will be generated. To manage the vault an administrative user is required.
  5. Unseal the vault. Unencrypt the database backend to use the service with at least three commands and three different unseal keys generated during the initialization step.
  6. Login with the administrative user and enable vault engine to store values (or generate tokens, passwords, and so on). The example here enables the secret engine to store key:value backend. Check out the secrets engines – https://www.vaultproject.io/docs/secrets

STEP 1) Summary of the mapped directories in the docker

Three directories are preserved:

  • /vault/config – contains configuration files in HCL or JSON format.
  • /vault/data – the place, where the encrypted database files will be kept only if a similar storage engine is used like “file” or “raft” storages. More information here – https://www.vaultproject.io/docs/configuration/storage
  • /vault/log – writing persistent audit logs. This feature should be enabled explicitly in the configuration.

The base directory used is /srv/vault/. And the three direcotries are created as follow and will be mapped in the docker container:

mkdir -p /srv/vault/config /srv/vault/data /srv/vault/log

The server’s directory /srv/vault/config will be mapped in docker’s directory /vault/config and the other two, too.

STEP 2) Initial base configuration

The initial configuration file is placed in /vault/config/config.hcl and is using HCL format – https://github.com/hashicorp/hcl. The initial configuration is minimal:

storage "raft" {
  path    = "/vault/data"
  node_id = "node1"

listener "tcp" {
  address     = ""
  tls_disable = 1

disable_mlock = true

api_addr = ""
cluster_addr = ""
ui = true

Place the file in /srv/vault/config/config.hcl

STEP 3) Start the Hashicorp vault server in docker

Mapping the three directories.

root@srv ~ # docker run --cap-add=IPC_LOCK -v /srv/vault/config:/vault/config -v /srv/vault/data:/vault/data -v /srv/vault/logs:/vault/logs --name=srv-vault vault server
==> Vault server configuration:

             Api Address:
                     Cgo: disabled
         Cluster Address:
              Go Version: go1.14.7
              Listener 1: tcp (addr: "", cluster address: "", max_request_duration: "1m30s", max_request_size: "33554432", tls: "disabled")
               Log Level: info
                   Mlock: supported: true, enabled: false
           Recovery Mode: false
                 Storage: raft (HA available)
                 Version: Vault v1.5.3
             Version Sha: 9fcd81405feb320390b9d71e15a691c3bc1daeef

==> Vault server started! Log data will stream in below:

Keep on reading!

Add cachecade SSD to an existing virtual drive in AVAGO MegaRAID with storcli64

Increase the IO performance of big storage consisting of hard drives with the CacheCade feature with MegaRAID hardware controllers. Here are the commands to ensure adding an SSD to cache storage of hard drives and the whole output:

storcli64 /c0 add VD cachecade r0 drives=252:0 WB
storcli64 /c0/v0 set ssdcaching=on

Summary and explanation

  • The controller used is AVAGO MegaRAID SAS9361-4i
  • Three 12T hard drives and 1 SSD 1T.
  • RAID5 of 3 hard drive. The name of the virtual drive is v0.
  • The CacheCade is in RAID0. The name of the virtual drive is v1.
  • The CacheCade is in WriteBack mode. The WriteBack mode is dangerous when the CacheCade device is RAID0, because there is no redundancy, but it’s OK if the purpose of the machine is just a proxy cache. WriteBack mode leads to much more performance to gain from the cache device over slow device sotrage, but should be carefully planned when using RAID0 cache (or single) device.
  • Using storcli – the cli command line tool to manage a (LSI) MegaRAID.
  • Add CacheCade RAID0 device by the first command. It will create a virtual drive RAID0 with the name v1.
  • Ensure the caching is enabled for the virtual device it should be by explicitly setting it with the second command. Adding only a CacheCade device may not add the cache virtual device to the existing virtual devices!

Output of a real world example

Keep on reading!

multiple random crashes of firefox in a docker container under Linux

Multiple random crashes in Firefox under Linux, when started in a docker container with errors of the kind:

[myuser@92ee57f7f63a ~]$ Exiting due to channel error.
Exiting due to channel error.
[myuser@92ee57f7f63a ~]$ firefox 
ExceptionHandler::GenerateDump cloned child 4864
ExceptionHandler::SendContinueSignalToChild sent continue signal to child
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Bus error (core dumped)
[myuser@92ee57f7f63a ~]$ 
###!!! [Parent][MessageChannel] Error: (msgtype=0x5A001C,name=PHttpChannel::Msg_DeleteSelf) Channel error: cannot send/recv
###!!! [Parent][MessageChannel] Error: (msgtype=0x5A001C,name=PHttpChannel::Msg_DeleteSelf) Channel error: cannot send/recv
###!!! [Parent][MessageChannel] Error: (msgtype=0x5A001C,name=PHttpChannel::Msg_DeleteSelf) Channel error: cannot send/recv
###!!! [Parent][MessageChannel] Error: (msgtype=0x5A001C,name=PHttpChannel::Msg_DeleteSelf) Channel error: cannot send/recv
###!!! [Parent][MessageChannel] Error: (msgtype=0x5A001C,name=PHttpChannel::Msg_DeleteSelf) Channel error: cannot send/recv

The chances to stop these multiple random crashes if you just increase the memory for the /dev/shm device in the docker container is really good! The default values in the docker /dev/shm are really low (in the tested machine only 64Mbytes) and the recommended values are at least 2Gbytes. More shared tabs more shared memory is needed.

Such strange and random crashes might cause a testing case to fail in an automation testing suite using the Selenium driver to start a Firefox headless instance.

To increase the shared memory size in the docker container, the container should be started with “–shm-size” option. For example:

docker run -it --shm-size=2048m my-gui-fedora:31

If the option –shm-size is missing (probably an old docker software) mapping an already mounted tmpfs directory in the host machine to the container is also a solution:

mkdir /dev/dockershm
mount -t tmpfs -o size=2048m tmpfs /dev/shmdocker
chmod 1777 /dev/shmdocker
docker run -d -v /mnt/shmdocker:/dev/shm my-gui-fedora:31

Remounting in the docker container is also possible:

srv myuser # docker exec -it my-gui bash
[myuser@92ee57f7f63a ~]$ sudo mount -o remount,size=2048m /dev/shm

Note the container should be run with –privileged option to be able to remount the /dev/shm.

The build docker command also has the –shm-size for the purpose of the building process not changing the default shared memory size in the containers based on the image afterward.

Using xtrabackup to make fast MySQL backups – backup and restore

Percona provides a really interesting tool for MySQL backups! It works on a live running MySQL server by copying the MySQL binary files from the data directory and because the tool knows how the engines work (InnoDB, MyISAM, and so on) it can make point-in-time consistent MySQL data files. Of course, using this tool on a database with InnoDB tables only is the best case, because no write lock will be used.

There are two main tasks when making a backup and one, which is not mandatory:

  1. Execute xtrabackup with –backup option to copy the MySQL data files and additional information for the tool
  2. Execute xtrabackup with –prepare option to prepare the MySQL (InnoDB) files ready for use of a MySQL server. The files are consistented, i.e. the whole backup is consistent despite the copy of the different files that happened at different times.
  3. Execute xtrabackup with –prepare option again to further prepare the MySQL (InnoDB) files ready for use of a MySQL server. Additional preparation such as InnoDB log files and more. This step is not mandatory and it may be skipped because the MySQL server, which uses the data files, will create the InnoDB log files.

The directory with MySQL copied files contains not only the MySQL files but additional information plus my.cnf (MySQL current configuration) backup. The backup files may be prepared (and restore) in a different server than the original, on which the backup was made.

xtrabackup may enable compressing on-the-fly when copying the binary files with the option –compress but the steps to use (restore) the backup in a new server are different – additional step to decompress before prepare. So the above steps become:

  1. xtrabackup –backup –compress – copy and compress on-the-fly.
  2. xtrabackup –decompress – decompress the backup files
  3. xtrabackup –prepare – make point-in-time consistent MySQL data files, which are ready for a MySQL server.
  4. xtrabackup –prepare – additional preparation to make the start up of the MySQL server with those files faster.

And here is a real-world example:

STEP 1) Install the xtrabackup utility

yum install -y https://repo.percona.com/yum/percona-release-latest.noarch.rpm
yum install -y percona-xtrabackup-24 qpress

The percona-xtrabackup-24 provides the percona xtrabackup tool for backup of MySQL 5.1, 5.5, 5.6 and 5.7 servers, as well as Percona Server for MySQL with XtraDB. Install percona-xtrabackup-80 for use with MySQL 8 and later.
The whole output is included in the Bonus 3 section below.

STEP 2) Make backup

Make the backup. The datadir of the MySQL server is needed and a new direcotry for the backup files. The MySQL server is running and serving requests.

[root@srv ~]# xtrabackup --backup --slave-info --datadir=/var/lib/mysql/ --target-dir=/mnt/backups/sql-xtrabackup/
xtrabackup: recognized server arguments: --datadir=/var/lib/mysql --log_bin --server-id=1 --open_files_limit=5000 --innodb_buffer_pool_size=256M --innodb_log_buffer_size=32M --innodb_log_files_in_group=2 --innodb_flush_log_at_trx_commit=0 --innodb_file_per_table=1 --innodb_flush_method=O_DIRECT --datadir=/var/lib/mysql/ 
xtrabackup: recognized client arguments: --password=* --backup=1 --slave-info=1 --target-dir=/mnt/backups/sql-xtrabackup/ 
200919 14:35:11  version_check Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup' (using password: YES).
200919 14:35:11  version_check Connected to MySQL server
200919 14:35:11  version_check Executing a version check against the server...
200919 14:35:11  version_check Done.
200919 14:35:11 Connecting to MySQL server host: localhost, user: not set, password: set, port: not set, socket: not set
Using server version 5.7.31-log
xtrabackup version 2.4.20 based on MySQL server 5.7.26 Linux (x86_64) (revision id: c8b4056)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /var/lib/mysql/
xtrabackup: open files limit requested 5000, set to 5000
xtrabackup: using the following InnoDB configuration:
xtrabackup:   innodb_data_home_dir = .
xtrabackup:   innodb_data_file_path = ibdata1:12M:autoextend
xtrabackup:   innodb_log_group_home_dir = ./
xtrabackup:   innodb_log_files_in_group = 2
xtrabackup:   innodb_log_file_size = 50331648
xtrabackup: using O_DIRECT
InnoDB: Number of pools: 1
200919 14:35:11 >> log scanned up to (1135932912)
xtrabackup: Generating a list of tablespaces
InnoDB: Allocated tablespace ID 34 for mywordpress/wp_users, old maximum was 0
200919 14:35:12 [01] Copying ./ibdata1 to /mnt/backups/sql-xtrabackup/ibdata1
200919 14:35:12 >> log scanned up to (1135932912)
200919 14:35:13 >> log scanned up to (1135932912)
200919 14:35:14 [01]        ...done
200919 14:35:14 >> log scanned up to (1135932912)
200919 14:35:15 >> log scanned up to (1135932912)
200919 14:35:16 [01] Copying ./mywordpress/wp_users.ibd to /mnt/backups/sql-xtrabackup/mywordpress/wp_users.ibd
200919 14:35:16 [01]        ...done
200919 14:35:16 [01] Copying ./mywordpress/wp_gglcptch_whitelist.ibd to /mnt/backups/sql-xtrabackup/mywordpress/wp_gglcptch_whitelist.ibd
200919 14:35:16 [01]        ...done
200919 14:35:16 [01] Copying ./mywordpress/wp_usermeta.ibd to /mnt/backups/sql-xtrabackup/mywordpress/wp_usermeta.ibd
200919 14:35:16 [01]        ...done
200919 14:35:16 >> log scanned up to (1135932912)
200919 14:35:17 [01] Copying ./mywordpress/wp_postmeta.ibd to /mnt/backups/sql-xtrabackup/mywordpress/wp_postmeta.ibd
200919 14:35:17 [01]        ...done
200919 14:35:17 [01] Copying ./mywordpress/wp_posts.ibd to /mnt/backups/sql-xtrabackup/mywordpress/wp_posts.ibd
200919 14:35:17 >> log scanned up to (1135932912)
200919 14:35:18 >> log scanned up to (1135932912)
200919 14:35:19 [01]        ...done
200919 14:35:19 >> log scanned up to (1135932912)
200919 14:36:30 [01] Copying ./mysql/columns_priv.MYD to /mnt/backups/sql-xtrabackup/mysql/columns_priv.MYD
200919 14:36:30 [01]        ...done
200919 14:36:30 >> log scanned up to (1135933567)
200919 14:36:31 [01] Copying ./mysql/proxies_priv.frm to /mnt/backups/sql-xtrabackup/mysql/proxies_priv.frm
200919 14:36:31 [01]        ...done
200919 14:36:31 [01] Copying ./mysql/help_category.frm to /mnt/backups/sql-xtrabackup/mysql/help_category.frm
200919 14:36:31 [01]        ...done
200919 14:36:31 [01] Copying ./mysql/proc.frm to /mnt/backups/sql-xtrabackup/mysql/proc.frm
200919 14:36:31 [01]        ...done
200919 14:36:31 Finished backing up non-InnoDB tables and files
200919 14:36:31 [00] Writing /mnt/backups/sql-xtrabackup/xtrabackup_slave_info
200919 14:36:31 [00]        ...done
200919 14:36:31 [00] Writing /mnt/backups/sql-xtrabackup/xtrabackup_binlog_info
200919 14:36:31 [00]        ...done
200919 14:36:31 Executing FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS...
xtrabackup: The latest check point (for incremental): '1135933558'
xtrabackup: Stopping log copying thread.
.200919 14:36:31 >> log scanned up to (1135933567)

200919 14:36:32 Executing UNLOCK TABLES
200919 14:36:32 All tables unlocked
200919 14:36:32 [00] Copying ib_buffer_pool to /mnt/backups/sql-xtrabackup/ib_buffer_pool
200919 14:36:32 [00]        ...done
200919 14:36:32 Backup created in directory '/mnt/backups/sql-xtrabackup/'
MySQL binlog position: filename 'srv-bin.000001', position '1004'
200919 14:36:32 [00] Writing /mnt/backups/sql-xtrabackup/backup-my.cnf
200919 14:36:32 [00]        ...done
200919 14:36:32 [00] Writing /mnt/backups/sql-xtrabackup/xtrabackup_info
200919 14:36:32 [00]        ...done
xtrabackup: Transaction log of lsn (1135932903) to (1135933567) was copied.
200919 14:36:33 completed OK!

In the end, there must be written: “completed OK!”.
The whole output of the command is included in the Bonus 1 section below. An example with compress option enabled is in Bonus 2 section below.
Here is what contains the backup diectory:
Keep on reading!