GNS3 + Centos 7.x

This and this (or it doesn't start).

Access VirtualBox guests from host and vice versa

In order to communicate between your VM's and host, add a host-only network adapter on the VM properties.  The IP associated with this adapter will be reachable by the host.

Useful commands for checking Linux hardware specs - memory, CPU, serial number

Server model
# dmidecode | grep -A3 '^System Information'

CPU model
# cat /proc/cpuinfo | grep 'model name' | uniq

Memory summary
# dmidecode -t 17 | grep MB

CPU config - good summary, check socket and core outputs for physicals
# lscpu

CPU config - more detail
# less /proc/cpuinfo

CPU config - just the number of cores, physical and virtual
# nproc

Serial number
# dmidecode -s system-serial-number
# dmidecode | grep Serial

If no root / sudo access (might not work on Debian-based distros, tested on RHEL)
$  lshal | grep system.hardware.serial

Logitech Z323 Speaker Hints

Having purchased my Z323's somewhat hastily and without any prior consultation of reviews a couple of weeks back, I was somewhat underwhelmed by their output. I purchased them to connect to my PC for listening to a variety of music types in my small study, and it just seemed like there was a big chunk of frequency reproduction missing somewhere in the midrange. I'm currently into emo'ish instrumental pop/rock and trancey stuff, which is admittedly quite acoustically demanding.

Bass was ok, not exactly punchy, but nevertheless adequate. Overall, there just seemed to be an absence of "snap" in the audio reproduction. The last set of 2.1's I bought was many years ago (Creative Cambridge Soundworks 2.1) and the Logitechs just didn't seem to measure up to that aged benchmark.

I've not had much time to spend with my new acquisition, but after some tweaking this afternoon the following facts became apparent:

- The midrange does seem to improve after some breaking in (my set is only now going into the first couple of hours of sustained playback and seems to be becoming a bit more "flexible" as time passes).

- One of the reviews on Amazon.com recommended turning the sats around to face the wall - this made a big difference to the perceived audio reproduction. There is a sweet spot here, but if your desk faces a wall and you have these speakers give it a go and see. Disadvantage is that the speaker volume control is now facing away from you, but I can live with that.

- Stereo imaging is good with a very broad field - seems you can put the sats almost anywhere and still maintain a nice soundstage.

- Moving the sub down to the floor and closer to the wall made the bass a bit more generalised, but now it seems to have difficulty keeping up. I can hear it lazily whoomping away, but seems to be a bit laboured. Maybe this will also improve with time and some more fine tuning of location. Turning the bass dial down a few notches helped - there is almost an exact point at which it goes from nicely accompanying the music to becoming "whoompy", for want of a better word...

I suppose my expectations here exceeded my budget, but Logitech speakers generally seem to be reasonably good all rounders. Definitely happier now than before, hopefully this info is useful to somebody else out there as well :-).

Zimbra error - Unable to determine enabled services from ldap

Symptoms: Zimbra users unable to log in to webmail, admin user unable to log into web interface, error "Unable to determine enabled services from ldap" if issuing command
$ opt/zimbra/bin/zmcontrol start

Cause: Zimbra's internal certificate has expired

Fix (as root):

# /opt/zimbra/bin/zmcertmgr createca -new
# /opt/zimbra/bin/zmcertmgr createcrt -new -days 365
# /opt/zimbra/bin/zmcertmgr deploycrt self
# /opt/zimbra/bin/zmcertmgr deployca
# su zimbra
$ /opt/zimbra/bin/zmcontrol restart

Windows Vista – Control Panel Inaccessible

If you cannot access your Windows Vista Control Panel, try this:

Select Start button –> Run –> enter “sfc /scannnow” –> Select OK

System files will be checked and repaired if possible; you might be prompted for your original Vista install media so that corrupted files can be replaced.

Making a Bootable Ubuntu USB Flash Drive Using Isostick.sh

If, like me, you're too lazy to find a blank CD every time you want to try a new flavour of Ubuntu, these instructions might be useful. This needs to be done on an Internet-connected Linux machine, follow these steps at your own peril (worked for me):

1. If you haven't done so yet, get your favourite Ubuntu .iso file here

2. Whilst it is downloading, get the isostick.sh script here

3. Install syslinux : $ sudo apt-get install syslinux

4. Observe the output of : $ sudo fdisk -l

5. Pop in your empty >= 1GB USB flash drive and repeat step 4, noting the additional lines to indicate the presence of your flash drive. You want to find its path which will be something like /dev/sdb1 or /dev/sdc1. For the remainder of this example, we will use the unlikely address of /dev/sdz/ and /dev/sdz1 - insert the address relevant to your own system.

CAUTION: be sure - if you're not sure, remove any other external storage devices and try steps 4 and 5 again. If you're still not sure, don't proceed. Save yourself the chilling horror of discovering that you've just nuked something you didn't mean to. Seriously. Be sure.

6. Just to be safe, unmount your flash drive (in the event of the OS having mounted it automatically) : $ sudo umount /dev/sdz1

7. Now we need to partition your flash drive (note that we're referring to the drive itself here, not an individual partition, so we omit the 1 from the end of the path) : $ fdisk /dev/sdz

8. Enter p to list existing partitions on the drive, enter d to delete them (follow the prompts), enter n to create a new partition (follow the prompts), enter t and set the type to 6, enter a followed by 1 to make your new partition bootable, enter w to write the changes and your flash drive should now be partitioned with a FAT16 partition, ready for formatting

8. Enter : $ sudo mkfs.msdos /dev/sdz1

9. To save some hassles, copy your Ubuntu .iso and the isostick.sh script to the same folder and cd to it in your command line. Alternately enter the full paths in the following command.

10. To actually write the image to the disk using isostick (no need to be alarmed by the error messages) : $ sudo isostick.sh ubuntu-9.04-desktop-i386.iso /dev/sdz1

11. See if it boots - remember that not all PC's will automatically boot from a USB device - you might need to set your boot order in your BIOS when the PC is starting up, or look for an instruction to press a certain key to access the boot menu / boot options during startup (before the OS starts loading).

Credits and links:

Thanks to ricey for his useful page over here, which put me onto the isostick.sh script

Additional information from our Ubuntu friends on USB booting

One source for the elusive isostick.sh script