Adventures & experiences in contemporary technology
While some Linux distros like Fedora install VirtualBox drivers during installation time, I prefer to install the VirtualBox Guest Additions themselves. Before doing this, it is best to remove the virtualbox-guest-additions package from Fedora to avoid conflicts. After that, execute the following command to ensure that all prerequisites for the VirtualBox Guest Additions are in place prior to mounting the VirtualBox Guest Additions ISO image and installing from there:
sudo dnf -y install gcc automake make kernel-headers dkms bzip2 libxcrypt-compat kernel-devel perl
During the installation, you may encounter a message like the following:
ValueError: File context for /opt/VBoxGuestAdditions-<VERSION>/other/mount.vboxsf already defined
This is generated by SELinux so the following commands need executing before the VirtualBox Guest Additions installation is repeated:
sudo semanage fcontext -d /opt/VBoxGuestAdditions-<VERSION>/other/mount.vboxsf
sudo restorecon /opt/VBoxGuestAdditions-<VERSION>/other/mount.vboxsf
Without doing the above step and fixing the preceding error message, I had an issue with mounting of Shared Folders whereby the mount point was set up but no folder contents were displayed. This happened even when my user account was added to the vboxsf group and it proved to be the SELinux context issue that was the cause.
Over the weekend, I finally got to fixing a problem that has affected Ubuntu 18.04 virtual machine for quite a while. The usual checks on Guest Additions installation and vboxsf group access assignment were performed but were not causing the issue. Also, no other VM (Windows (7 & 10) and Linux Mint Debian Edition) on the same Linux Mint 19.2 machine was experiencing the same issue. The latter observation made the problem intrinsic to the Ubuntu VM itself.
Because I install the Guest Additions software from the included virtual CD, I executed the following command to open the relevant file for editing:
sudo systemctl edit --full vboxadd-service
If I had installed installed virtualbox-guest-dkms and virtualbox-guest-utils from the Ubuntu repositories instead, then this would have been the command that I needed to execute instead of the above.
sudo systemctl edit --full virtualbox-guest-utils
Whichever configuration gets opened, the line that needs attention is the one beginning with Conflicts (line 6 in the file on my system). The required edit removes systemd-timesync.service from the list following the equals sign. It is worth checking that file paths include the correct version number for the Guest Additions software that is installed in case this was not the case. The only change that was needed on my Ubuntu VM was to the Conflicts line and rebooting it got the Shared Folder automatically mounted under the /media directory as expected.
BASH is a command-line interpretor that is commonly used by Linux and UNIX operating systems. Chances are that you will find find yourself in a BASH session if you start up a terminal emulator in many of these though there are others like KSH and SSH too.
BASH comes with its own configuration files and one of these is located in your own home directory, .bashrc. Among other things, it can become a place to store command shortcuts or aliases. Here is an example:
alias us=’sudo apt-get update && sudo apt-get upgrade’
Such a definition needs there to be no spaces around the equals sign and the actual command to be declared in single quotes. Doing anything other than this will not work as I have found. Also, there are times when you want to update or add one of these and use it without shutting down a terminal emulator and restarting it.
To reload the .bashrc file to use the updates contained in there, one of the following commands can be issued:
source ~/.bashrc
. ~/.bashrc
Both will read the file and execute its contents so you get those updates made available so you can continue what you are doing. There appears to be a tendency for this kind of thing in the world of Linux and UNIX because it also applies to remounting drives after a change to /etc/fstab and restarting system services like Apache, MySQL or Nginx. The command for the former is below:
sudo mount -a
Often, the means for applying the sorts of in-situ changes that you make are simple ones too and anything that avoids system reboots has to be good since you have less work interruptions.
In a previous posting, I talked about compressing a virtual hard disk for a Windows guest system running in VirtualBox on a Linux system. Since then, I have needed to do the same for a Linux guest following some housekeeping. The Linux distribution used is Debian so the instructions are relevant to that and maybe its derivatives such as Ubuntu, Linux Mint and their kind.
While there are other alternatives like dd, I am going to stick with a utility named zerofree to overwrite the newly freed up disk space with zeroes to aid compression later on in the process for this and the first step is to install it using the following command:
apt-get install zerofree
Once that has been completed, the next step is to unmount the relevant disk partition. Luckily for me, what I needed to compress was an area that I reserved for synchronisation with Dropbox. If it was the root area where the operating system files are kept, a live distro would be needed instead. In any event, the required command takes the following form with the mount point being whatever it is on your system (/home, for instance):
sudo umount [mount point]
With the disk partition unmounted, zerofree can be run by issuing a command that looks like this:
zerofree -v /dev/sdxN
Above, the -v switch tells zerofree to display its progress and a continually updating percentage count tells you how it is going. The /dev/sdxN piece is generic with the x corresponding to the letter assigned to the disk on which the partition resides (a, b, c or whatever) and the N is the partition number (1, 2, 3 or whatever; before GPT, the maximum was 4). Putting all this together, we get an example like /dev/sdb2.
Once, that had completed, the next step is to shut down the VM and execute a command like the following on the host Linux system ([file location/file name] needs to be replaced with whatever applies on your system):
VBoxManage modifyhd [file location/file name].vdi --compact
With the zero filling in place, there was a lot of space released when I tried this. While it would be nice for dynamic virtual disks to reduce in size automatically, I accept that there may be data integrity risks with those so the manual process will suffice for now. It has not been needed that often anyway.
Once you end up with Windows overwriting your master boot record (MBR), you have lost the ability to use GRUB. Therefore, it would be handy to get it back if you want to start up Linux again. Though the loss of GRUB from the MBR was a deliberate act of mine, I knew that I’d have to restore GRUB to get Linux working again.So, I have been addressing the situation with a Live DVD for the likes of Ubuntu or Linux Mint. Once one of those had loaded its copy of the distribution, issuing the following command in a terminal session gets things back again:
sudo grub-install --root-directory=/media/0d104aff-ec8c-44c8-b811-92b993823444 /dev/sda
When there were error messages, I tried this one to see if I could get more information:
sudo grub-install --root-directory=/media/0d104aff-ec8c-44c8-b811-92b993823444 /dev/sda --recheck
Also, it is possible to mount a partition on the boot drive and use that in the command to restore GRUB. Here is the required combination:
sudo mount /dev/sda1 /mnt
sudo grub-install --root-directory=/mnt /dev/sda
Either of these will get GRUB working without a hitch and they are far more snappy than downloading Boot-Repair and using that; I was doing that for a while until a feature on triple booting appeared in an issue of Linux User & Developer that reminded me of the more readily available option. Once, there was a need to manually add an entry for Windows 7 to the GRUB menu too and, with that instated, I was able to dual-boot Ubuntu and Windows using GRUB to select which one was to start for me. Since then, I have been able to dual boot Linux Mint and Windows 8.1 with GRUB finding the latter all by itself so your experiences too may show this variation so it’s worth bearing in mind.
The official line from Western Digital is that they do not support the use of their My Book Live NAS drives with Linux or UNIX. However, what that means is that they only develop tools for accessing their products for Windows and maybe OS X. It still doesn’t mean that you cannot access the drive’s configuration settings by pointing your web browser at http://mybooklive.local/. In fact, not having those extra tools is no drawback at all since the drive can be accessed through your file manager of choice under the Network section and the default name is MyBookLive too so you easily can find the thing once it is connected to a router or switch anyway.
Once you are in the servers web configuration area, you can do things like changing its name, updating its firmware, finding out what network has been assigned to it, creating and deleting file shares, password protecting file shares and other things. These are the kinds of things that come in handy if you are going to have a more permanent connection to the NAS from a PC that runs Linux. The steps that I describe have worked on Ubuntu 12.04 and 13.10 with the GNOME desktop environment.
What I was surprised to discover that you cannot just set up a symbolic link that points to a file share. Instead, it needs to be mounted and this can be done from the command line using mount or at start-up with /etc/fstab. For this to happen, you need the Common Internet File System utilities and these are added as follows if you need them (check on the Software Software or in Synaptic):
sudo apt-get install cifs-utils
Once these are added, you can add a line like the following to /etc/fstab:
//[NAS IP address]/[file share name] /[file system mount point] cifs
credentials=[full file location]/.creds,
iocharset=utf8,
sec=ntlm,
gid=1000,
uid=1000,
file_mode=0775,
dir_mode=0775
0 0
Though I have broken it over several lines above, this is one unwrapped line in /etc/fstab with all the fields in square brackets populated for your system and with no brackets around these. Though there are other ways to specify the server, using its IP address is what has given me the most success and this is found under Settings > Network on the web console. Next up is the actual file share name on the NAS and I have used a custom them instead of the default of Public. The NAS file share needs to be mounted to an actual directory in your file system like /media/nas or whatever you like and you will need to create this beforehand. After that, you have to specify the file system and it is cifs instead of more conventional alternatives like ext4 or swap. After this and before the final two space delimited zeroes in the line comes the chunk that deals with the security of the mount point.
What I have done in my case is to have a password protected file share and the user ID and password have been placed in a file in my home area with only the owner having read and write permissions for it (600 in chmod-speak). Preceding the filename with a “.” also affords extra invisibility. That file then is populated with the user ID and password like the following. Of course, the bracketed values have to be replaced with what you have in your case.
username=[NAS file share user ID]
password=[NAS file share password]
With the credentials file created, its options have to be set. First, there is the character set of the file (usually UTF-8 and I got error code 79 when I mistyped this) and the security that is to be applied to the credentials (ntlm in this case). To save having no write access to the mounted file share, the uid and gid for your user needs specification with 1000 being the values for the first non-root user created on a Linux system. After that, it does no harm to set the file and directory permissions because they only can be set at mount time; using chmod, chown and chgrp later on has no effect whatsoever. Here, I have set permissions to read, write and execute for the owner and the user group while only allowing read and execute access for everyone else (that’s 775 in the world of chmod).
All of what I have described here worked for me and had to gleaned from disparate sources like Mount Windows Shares Permanently from the Ubuntu Wiki, another blog entry regarding the permissions settings for a CIFS mount point and an Ubuntu forum posting on mounting CIFS with UTF-8 support. Because of the scattering of information, I just felt that it needed to all together in one place for others to use and I hope that fulfils someone else’s needs in a similar way to mine.
By default, I think that Windows plants its temporary files in c:\windows\temp. In Linux or in Ubuntu at least, the equivalent area is /tmp. However, not realising that /tmp when you shut down and start your PC could cause the silly blunder that I made today. I was doing a spot of reorganisation on my spare PC when I dumped some files in /tmp from a hard drive that I had added. I was reformatting the drive as ext3 following its NTFS former life. As part of this, I was editing fstab to automount the thing and a system restart ensued. I ended up losing whatever I put into /tmp, a very silly blunder. Luckily, I had the good sense not to put anything critical in there so nothing of consequence has been lost. Nevertheless, a lesson has been learnt: Windows allows its temporary area to pick up all kinds of clutter until you clear it while Linux clears the thing regularly. It’s amazing how Windows thinking can cause a howler when you have a lapse of concentration using a *NIX operating system, even for someone who uses the latter every day.