Geekdom

Getting iPhones, iPads and other iDevices to Print

Rich — Tue, 17 Jan 2012 21:47:39 +0000

БогородицаiDevices like the iPhone and iPad have the ability to print to select “supported” printers. Basically, those printers are just broadcasting Apple’s bonjour service to which the iDevice detects natively.

However, those “supported” printers aren’t all that readily available and corporate environments being inundated with iDevices can’t rightly replace all of their printers.

With a standard CUPS server, the avahi-daemon, and a simple python script, this can be easily solved! Grab the script from https://github.com/tjfontaine/airprint-generate and run it against your installed CUPS printers.

Avahi/Bonjour is a protocol that does not cross subnets. If you have a need for this, which is a typical corporate need, check out http://www.grouplogic.com/Knowledge/PDFUpload/Info/WanBonjour_1.pdf

Recovering a Linux LVM due to lost information on a single member drive

Rich — Thu, 29 Dec 2011 22:48:36 +0000

ikoniIf an LVM partition table or data containing the LVM information on the physical volume is ever lost, there is a way back out

First, boot the system without the volume active. Get in to single user.
Second, identify the device in question. In this example, let’s say /dev/sdb1 has lost its LVM information.
Third, find the latest archive of the volume information in /etc/lvm/archive which contains the UUID that the system cannot find, but you are sure it is the disk that has had its volume information overwritten or lost (in this example, let’s say the file is MyLVMgroupA.vg)
Fourth, run pvcreate to restore the information:
pvcreate –uuid –restorefile /etc/lvm/archive/MyLVMgroupA.vg -ff /dev/sdb1
Fifth, reboot and all is good. Run an fsck just to be on the safe side!

Fedora 16 quirk

Rich — Thu, 29 Dec 2011 20:27:36 +0000

Fedora has become rather dramatic in its fast moving changes. Fedora of today is what RHEL will become, and the system as a whole will look entirely different. systemctl is one of the bigger changes, and going from Fedora 14 to Fedora 15 wasn’t that painl since most services transferred over with ease. However, going from Fedora 15 to Fedora 16, some key services got renamed.

It’s best to do a systemctl command prior to any upgrade to record what you had running previously. The NFS server, for example, is one such service that gets renamed and, thus, will not automatically start on an upgraded system due to the name change. To correct this:

systemctl enable nfs-server.service

Linux Logical Volumes

Rich — Thu, 29 Dec 2011 20:24:32 +0000

Fedora, as do other distros, freaks out when you add a physical drive to a system which had been previously part of another logical volume. This doesn’t happen often, but if it does, the symptom is when you run system-config-lvm and it exits unexpectedly with:

'NoneType' object is not iterable

The way to resolve this is to fdisk the new disk on the system, create a partition on it, and write that partition table back to the disk. This overwrites the previous LVM information.

Linux KVM and the virtual firewall

Rich — Sun, 30 Oct 2011 22:26:26 +0000

KVM offers a slew of opportunities for home or business and a feature set that is ever growing. Some setups can be more complex than others, and incorporating a virtual firewall in to your existing KVM guests pushes the boundaries.

Internet --- KVM host
             virtual firewall -- virtual hosts (internal) -- physical virtual host

The design is a little atypical as it consolidates a physical firewall in to the same pool of systems as internal hosts that wish to remain secure, but with care this can be done entirely securely. For this to work, the KVM host must have two NICs.

From personal experience, ipCop, pfSense, and ClearOS were the firewalls to consider. Requirements are (1) stable and (2) easy to administer by even the most novice user, which translates to (2a) a web interface.

ipCop has been around for a long while and works well. However, it requires nightly reboots (yuck) and is not as easy to administer. Thus, it was chosen to skip over ipCop as a KVM guest firewall.

pfSense is an excellent firewall and tends to play somewhat well as a KVM firewall. FreeBSD 7 (what pfSense is based off of) does not have native support as a KVM guest, though, and won’t take advantage of virtio without some tinkering. Regardless, it is simple plug and play and a heck of a workhorse. However, enter in some extreme loads of traffic (torrent, anyone?), and pfSense frequently locks up. This was the same experience when running as a hardware firewall, yet all postings out there make this situation sound like an anomaly that should never exist.

ClearOS appears promising with its slick interface and linux kernel support as a native guest. With it being based off of RHEL 5.2, its kernel is somewhat older (2.6.18 as of this writing) and its KVM support is limited, but it is there. It worked right out of the box and was simple to configure. The deal breaker on this one is that it cannot port forward to other KVM guests on the same KVM host. This is a bit of a mystery and rather odd!

KVM is the way to go. For now, stay within the mold, though.