When I tried to spin up my CentOS 7 guest—running on kernel 3.10 within VirtualBox 6.0.10—the boot process didn’t behave as expected. Instead of reaching a stable login prompt, the system stalled mid-way through the startup sequence.

Upon inspecting the console logs, I noticed two critical error messages that pointed to exactly where things were breaking down: [FAILED] Failed to start Virtual Machine and Container Registration Service and [FAILED] Failed to start Login Service.

At this stage, I wasn’t entirely certain of the smoking gun. It looked like a potential issue with the SELinux configuration—specifically how it was interacting with the system’s boot state—but I also had to consider that this might be a known bug within VirtualBox 6 itself. Regardless of the exact culprit, these two service failures were preventing me from accessing my environment.

Prerequisites for Troubleshooting

Before diving into the fix, I made sure I had a few things in place—this approach means editing system files during boot, so a little preparation goes a long way:

• Access to the VirtualBox console. You need to be at the keyboard when the VM first powers on, ready to catch the GRUB menu before it hands off to the kernel. (My environment was a CentOS 7 guest on VirtualBox 6.0.10.)
• A snapshot or backup first. Since we’ll be remounting the filesystem and editing /etc/selinux/config, take a VirtualBox snapshot beforehand. If anything goes sideways, you can roll straight back.
• Comfort with a terminal editor. The fix happens in vi inside a minimal rescue shell, so basic vi navigation (insert, save, quit) is all you need.
• Knowing your boot entry. If GRUB lists multiple kernels, be ready to identify your primary CentOS entry—that’s the one we’ll edit.

Step 1: Revealing the Hidden Boot Errors (Exit Quiet Boot)

When I first encountered the boot failure, I was met with nothing but a static progress bar. By default, CentOS 7 uses a “quiet boot” setting that hides the technical minutiae of the startup process behind a clean splash screen. While this looks professional, it is incredibly unhelpful when you are troubleshooting a system that refuses to start.

To see what was actually happening under the hood, I needed to reveal the full system logs. As soon as the boot sequence begins, pressing the Esc key interrupts the quiet mode and displays the detailed text-based output. By doing this, I was finally able to see the specific [FAILED] messages—such as those regarding the Virtual Machine and Container Registration Service—that provided the first real clue into the system’s instability.

Step 2: Booting CentOS into Rescue Mode via GRUB

Once I realized the standard boot process was hitting a wall, my next move was to use the GRUB menu to bypass the failing services and drop straight into a command-line environment. It’s important to note that GRUB itself isn’t corrupt—it is still functioning perfectly as our entry point—we just need to change how it hands off control to the kernel.

Here is exactly how I navigated through the bootloader to enter rescue mode:

1. Select the Entry: When the VirtualBox window displays the GRUB boot menu, use your arrow keys to highlight your primary CentOS boot entry.
2. Edit the Boot Parameters: Press the e key on your keyboard. This opens an editor that allows you to modify the boot instructions before they are actually executed by the system.
3. Modify the Linux Line: Scroll down through the text until you find the line starting with linux16. This line contains the kernel-specific arguments and parameters. Navigate to the very end of this line, add a space, and append: systemd.unit=rescue.target
4. Execute the Boot: Once the parameter is added, press Ctrl+X (or F10) to boot with these new settings.

This process forces CentOS to skip the standard multi-user startup sequence—where the failing services are triggered—and instead boots you directly into a minimal, single-user rescue environment where we can address the SELinux configuration issues manually.

Step 3: Fixing the SELinux Configuration (the Root Cause)

Once I was settled into the rescue shell, my first task wasn’t editing files—it was making sure I could actually save them. Depending on how the system lands in rescue mode, the root filesystem can come up read-only, so to be safe I remounted it writable before touching anything:

mount -o remount,rw /

With write access secured, I turned my attention to the primary suspect: the SELinux configuration. SELinux sits deep in the boot path, and when its policy gets tangled up with the system’s state—as it can in a quirky VirtualBox guest—it’s capable of quietly stalling the very services CentOS needs to finish starting.

I opened the configuration file using vi:

vi /etc/selinux/config

Inside the file, I located the line starting with SELINUX=. Here is the detail that made this issue so hard to pin down: it wasn’t set to enforcing, as you might assume. It was already on permissive—a mode that is only supposed to log policy violations, not block anything. That’s precisely why SELinux is such an easy culprit to overlook here; on paper it shouldn’t have been able to stop those services at all. Yet they still refused to start. So rather than half-measures, I turned SELinux off completely:

SELINUX=disabled

Setting the mode to disabled takes SELinux fully out of the boot path on the next startup, which is what finally cleared the conflict stalling the Registration and Login services. I saved the file and exited the editor. (If you’d prefer to keep SELinux active for security, you can switch it back to enforcing once you’ve confirmed the VM boots reliably—but for getting a stuck machine running again, disabling it is the fastest, most decisive fix.)

Step 4: Verifying the Fix and Ruling Out the VirtualBox 6 Bug

After saving my changes in rescue mode, I performed a standard reboot to see if the system would finally reach the login prompt. This time, the boot sequence progressed smoothly; those alarming [FAILED] messages that had been stalling the startup process were nowhere to be seen.

To double-check my work, I ran getenforce once the system was up. The output came back Disabled, confirming SELinux was fully switched off and no longer interfering with the services that had been failing to initialize.

While the VM is now stable, I kept one caveat in mind: the environment involves VirtualBox 6.0.10. There have been documented instances of specific service failures linked to bugs within this particular version of the hypervisor. While correcting the SELinux configuration solved my immediate problem, if you encounter similar boot issues on a different machine even after following these steps, it is worth considering that the issue might reside in the VirtualBox software itself rather than your CentOS configuration.

The post How to Fix CentOS VM Client Boot Failure: A Step-by-Step Troubleshooting Guide appeared first on LarryLai.

Background

After installing WP Health, it’s shown that both MariaDB 5 (a default replacement of MySQL for CentOS7) and PHP5.6 are obsolete, i.e. no more formal support and no security patches will be released. It’s suggested to upgrade at least to MariaDB10 and PHP7.

Apart from security and support concern, it’s known that PHP7 has better performance than PHP5.

Issue

After upgrading, either the Virtualmin has problem in displaying submenu on the left panel or there’re “Internal Server Error” on some WordPress sites. It’s found out that during yum update MariaDB, it’s required to remove the old MariaDB5, however, for packages dependency needs, yum will at the same time remove Postfix and Virtualmin-base. If these 2 packages are reinstalled after upgrading to MariaDB, then WordPress has problem.

Solution

Use rpm -e –nodeps to skip removal of Postfix and Virtualmin-base.

Tricks

After removal PHP5.6, list out all the related packages, e.g. php-mysqlnd, php-gd, etc. depending on my case, there’re some others. All these have to be reinstalled after installing PHP7.2 base package.

For upgrade of PHP7, never upgrade to the lastest PHP7.3 as some of the PHP packages do not have PHP7.3 compatible rpm, only have PHP7.2 compatible rpm. There’re many CentOS PHP7 upgrade info. on the web, but some are not good, after try and error, I use TecAdmin.net’s advice and got no problem.

Config

• CentOS: 7.6
• Virtualmin 6.06
• WordPress 5.1
• MariaDB: 10.1

The post Centos7 Virtualmin Upgrade PHP7 MariaDB appeared first on LarryLai.

After updating iOS from version to 11, there are some installed apps not ready for this version.

The worst is that I stored all important passwords in an app called Keyring, but after iOS update, I cannot get any of the stored password because of incompatibility of this app with this iOS ver.

Solution: NO

The post iOS 11 incompatibility appeared first on LarryLai.

After moving mounted volumes from Qnap NAS to iMac as host with CentOS as client, the directory and file ownership cannot be changed to Apache at the client side. No matter using root or user privilege to command the chown.

Solution:

Add the following in iMac’s /etc/exports:

[nfsshare] -rw -maproot=root:wheel

Tricks:

-maproot directive can pass the root control from nfs host to client, without it even changing the directory access and file permission to 777 in host, or changing the mount options at client cannot solve the issue.

Config:

• OSX:        10.12.3
• CentOS:   7.3

The post Cannot Change Ownership on NFS Files appeared first on LarryLai.

“The selected virtual machine is inaccessible. Please inspect the error message shown below and press the Refresh button if you want to repeat the accessibility check.” After saving states of all virtual machines of VirtualBox running on Mac, rebooting the Mac host without any issue. Then it was a big surprised that all virtual machines are inaccessible. Not only the virtual hard disks, but all the virtual machines files.

Solution:

This case was caused by previously renaming the external SSD storing the virtual machine files. After renaming back to original disk name, still have to

• Remove the virtual machines and Add them back to VirtualBox by going to the VirtualBox application top bar
• Choose Machine -> Add
• Select the file with .vbox (that’s the virtual machine file, not the .vdi or .vmdk). In case, the there’s unexpected quit of VirtualBox, the .vbox may be corrupted, then it is necessary to rename the .vbox-prev to .vbox

Tricks:

• It is not easy to recognise that the issue was caused by renaming the path (in this case, the SSD disk) of the virtual machine as not until restarting VirtualBox, it is not observed there is any error on the virtual machines.
• Even after renaming back the path to the original one, VirtualBox still shows inaccessible virtual machine. The suggested solution of clicking the Refresh button located at bottom left cannot fix the problem. (Don’t know why Oracle is so stupid to suggest this!)
• The Machine -> Add appears only at the top bar of VirtualBox application, but not appear at the top bar of Oracle VM VirtualBox Manager
• It is easy to misinterpret the error message that it was due to inaccessible storage and it would be tempted to create new VM and access the same original storage, but it is not good in the sense that the virtual hard disk is located under the old VM’s directory.
• Mac users always have TimeMachine backup for the virtual machines, in such case restoring the VM directory is wasting time.

Config:

OS X           10.12.1

VirtualBox   5.0.28

The post VirtualBox VM Inaccessible on Mac appeared first on LarryLai.

Just bought a Wacom Intuos Draw CTL-690, and want to install a note taking app with drawing feature in iMac running OSX Mavericks, found a good one – MS OneNote, but it only support OSX 10.10 or above. Being aware of the possibility that the latest OSX Sierra does not fully support old Adobe CS5.5 Master Collection, I tried to upgrade to OSX Yosemite. After downloaded Yosemite install package on the web as it is unavailable on Apple’s support site any more.

There was error after verifying the system when running the Yosemite installer suggesting contact AppleCare.

Solution:

Directly upgrade to OSX 10.12 Sierra. There is some little problem with Photoshop. Need to install JavaSE again as instructed by Photoshop after upgrade.

Tricks:

• It is good practice to backup the old OS with Time Machine for Mac even though in my case, there is no need to restore to original OS version.
• If upgrading to Sierra has potential application incompatibility issue with new OS, I think there still may be some with Yosemite or El Capitan, why not give Sierra a try as it is 10.12.1 not the xx.xx.0 version.

Config:

• OSX 10.9.5 -> OSX 10.12.1
• Photoshop  12.1

The post Mac OS X Maverick Upgrade appeared first on LarryLai.

After installation of Android Studio, the Android Virtual Device (AVD) Manager cannot be started unless the running virtual machine (irrelevant to Android Studio deployment) in VirtualBox is shut down.

Solution:

1. Instead of creating virtual device, deploy physical Android device, (actually I’ve tried this approach) e.g. Samsung old or obsolete model in case you don’t want to spend too much money.
2. Install Genymotion which is also rely on VirtualBox, thus there is no conflict between this emulator with the other existing emulator from VirtualBox.

Tricks:

The AVD manager of Android Studio could not start because there is conflict between Android Studio’s emulator module with VirtualBox.

Config:

• Host OS: OpenSUSE 13.2
• IDE: Android Studio 2.1
• VirtualBox: 5.0.18
• Genymotion: 2.6.0

The post Android Studio: Cannot Start AVD Manager appeared first on LarryLai.

OpenSUSE suddenly could not boot to GUI mode, but being kicked out to recovery mode with the CLI mode with the warning of something like no space to write on device, and the hard disk activity light was unexpectedly always on.

Solution:

• At the recovery mode, login as root and delete some snapshots.
• Execute “snapper ls” to get the snapshot numbers
• Execute “snapper delete [start number] – [end number]”
• Reboot

Tricks:

1. This issue probably occurs only on linux system with btrfs partition in which snapshots are automatically generated. Thus, it should be paid extra care to decide whether to use traditional ext3 or ext4 instead of the default partition option: btrfs suggested by OpenSUSE during installation.
2. When typing “df -h”, the storage usage seems to be normal. No storage or any partition full could be noticed.
3. When hard disk activity light always on, it seems that something related to hardware is wrong but actually it doesn’t.
4. My partition config. fully agreed OpenSUSE suggestion that btrfs for / directory and xfs for /home directory. Yesterday, due to some video files transfer from desktop PC to iPhone using FTP, I setup FTP server on desktop using proftpd, the default directory on server side is /srv/ftp. Probably the new video files are so large that btrfs generated large snapshots under / directory.

Config:

• OpenSUSE 13.2
• KDE4 1.0

The post OpenSUSE Boot Up Issue appeared first on LarryLai.

Deleting the oldest snapshot of virtual machine in VirtualBox is often difficult, sometimes there is error with detail “more than one child hard disk”.

Solution:

Open VirtualBox control panel, select:

File->Virtual Media Manager

click on the Virtual child hard disk within the appropriate virtual machine (don’t check for other non-appropriate virtual machines) one by one, at the lower part of the panel, there are some information about the hard disk, “Type”, … “Attached to:”, etc., normally all child hard disk of the same virtual machine should be “attached to” the name of the Virtual machine, but at the problem child hard disk, the info. about the “Attached to” is Not Attached, then you can select “Remove” to take it out, if ask whether to “Keep” or “Remove”, for safety, you can keep the file, then go back to Snapshots to remove again the snapshot, the error should be gone.

Tricks:

• Similar error occur only on deleting the oldest snapshot but not recent snapshots.
• It is dangerous to just remove the hard disk file stored in the Snapshot directory of the virtual machine, and indeed remove snapshot process of Virtualbox is not just removal of virtual disk file, but some kind of merging the appropriate snapshot content with the current virtual hard disk. Inappropriate removing any snapshot files would be a nightmare to restart the virtual machine.
• In many forums, it is known that the error of deleting the first snapshot is a bug of VirtualBox for quite some years since ver. 3.x, but it still exists till this version 5. A shame to the technology giant, Oracle!

Config:

VirtualBox  5.0.10r104061

The post VirtualBox Delete Oldest Snapshot appeared first on LarryLai.

Uploaded keynote file to iCloud through safari, after a day the iPad still could not see it when clicking the “+” sign at top left corner of Keynote in iPad.

Solution:

Go to Settings in iOS device, click iCloud and turn it off for a while then turn it on again

Tricks:

People would ask why not using Google Drive to transfer the files. It is interesting that when you upload a keynote file to Google Drive, the file will become a set of files including data and various image files under a folder with the name of the keynote file, then it is useless to download it to the iOS, i.e. you cannot play anything about the original keynote file in your iOS devices.

Config:

iOS    9.1

The post Demystify iCloud Sync appeared first on LarryLai.