Author: Daniel Mettler

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Using multiple Skype accounts on macOS

With the recent changes in Skype, the “traditional” method of running several Skype instances using different system users doesn’t work anymore (as the the new authentication dialog strangely doesn’t get the focus anymore).

So, in order to use several Skype accounts on macOS (formerly known as Mac OS X), do the following:

  1. Open the Script Editor (in the ‘Utilities’ folder in the ‘Applications’ folder)
  2. Create a new script with the following content: 
    do shell script "open -na /Applications/Skype.app/Contents/MacOS/Skype --args -DataPath '/Users/your_system_user/Library/Application Support/Skype_any_identifier'"

    Replace your_system_user by your regular macOS user account (see ‘whoami’ in Terminal)
    Replace _any_identifier by the according Skype account name, e.g. _myskypename (doesn’t really matter what, just don’t use an empty string)
    Please mind the double quotes and single quotes (important!)

  3. Save the script as an application: File.. Save.., choose “Application” as file format, give it a name and store it e.g. in your home directory or in the Applications folder

Repeat these steps for any of your Skype accounts, giving each Skype account a different Skype_any_identifier. You can then start the according Skype instances by double clicking on the according app.

Explanation:

The above script starts a new instance of Skype (which would otherwise be prevented), using the -n argument. Each instance of Skype gets its own directory to store the according account data, using the -DataPath argument.

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How to check filesystems in a qcow2 image

A useful post how to fsck (check and fix) a filesystem in a qcow2 image (as typically used for KVM VMs, e.g. in Proxmox):

How to recover a qcow2 file using fsck

On Proxmox or Debian, one does the following:

Attention:

  • Make sure the according VM isn’t running, i.e. the partition not mounted
  • Adjust the commands below to match your system, use the correct qcow2 image, use the correct fsck-variant, fsck the correct filesystem, note that -p tries to automatically fix errors!
# modprobe nbd max_part=8
# qemu-nbd --connect=/dev/nbd0 /var/lib/vz/images/100/vm-100-disk-1.qcow2
# fdisk -l /dev/ndb0
/dev/nbd0p1            2048     7813119     3905536   82  Linux swap / Solaris
/dev/nbd0p2   *     7813120   119537663    55862272   83  Linux
# fsck.ext4 /dev/nbd0p2
# fsck.ext4 -p /dev/nbd0p2
# qemu-nbd --disconnect /dev/nbd0

Like this, one doesn’t need to boot the VM using a boot ISO/CDROM and can fix the filesystem right from the host node.

 

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Karabiner: Use PC-style Home/End keys on Mac OS X

Karabiner allows to customize almost any aspect of the keymap on Mac OS X in a convenient way:

Karabiner – A powerful and stable keyboard customizer for OS X. (formerly known as KeyRemap4MacBook)

For example, you can make the “Home” and “End” keys behave like on a PC. Regarding these two keys, I find the PC style behaviour more intuitive, e.g. using shift-home and shift-end to select text, rather than using the tricky three-finger-combinations shift-cmd-left_cursor and shift-cmd-right_cursor in Mac OS X.

Here’s how to configure this in Karabiner:

karabiner_use_pc_style_home_and_end_keys

 

Further, I decided to lower the “Key Repeat Delay Until Repeat” to 100 ms and the “Key Repeat” to 23 ms for quicker navigation and repetitive typing.

Of course, there are many other useful tweaks to explore.

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zpool: Symbol `spa_feature_table’ has different size in shared object, consider re-linking

If you see the following error message when executing ‘zpool status’ after “upgrading” Proxmox to the (currently) latest version with ZoL 0.6.4 instead of 0.6.3:

zpool: Symbol `spa_feature_table' has different size in shared object, consider re-linking

Explanation:

“Re-linking” doesn’t have a special meaning in ZFS/ZoL terminology, it rather just describes the usual linking step after compiling some source code.

Solution:

The most likely cause is that some new, updated and required packages have not been installed (e.g. with ‘uname -a’, you’ll see that the old kernel is still running, even after rebooting). Usually, this happens if one executes “apt-get update && apt-get upgrade” (as usual) rather than “apt-get update && apt-get dist-upgrade“. So, in order to solve this problem, do:

# apt-get update && apt-get dist-upgrade
# reboot

In this case, ZoL 0.6.4 also includes a couple of new features which can be enabled for all local ZFS pools by executing:

# zpool upgrade -a
This system supports ZFS pool feature flags.

Enabled the following features on 'rpool':
 spacemap_histogram
 enabled_txg
 hole_birth
 extensible_dataset
 embedded_data
 bookmarks
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Mac OS X tools: FinderPath and HyperDock

On hacker news (i.e the better alternative interface http://hckrnews.com), I stumbled over two nice helper apps for Mac OS X:

FinderPath (free) shows the full path in the title bar of a Finder window upon double-clicking it. Like that, the full path can be selected and copied to the clipboard or one can simply edit the path and hereby easily navigate through the filesystem trees. It’s quite a time saver!

HyperDock (9.95 USD) displays thumbnail screenshots of all windows of the running apps in the Dock when hovering over them, making it easier and quicker to switch to other windows or to close them (the latter being a feature still missing in Mission Control). It also supports several other cool features, like Window Snapping.

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Proxmox VE 3.4 and ZFS: How to create an ISO to use lz4 compression by default

EDIT 20150607: Meanwhile, this fix has been included by Proxmox – the current official Proxmox VE 3.4 Installer ISO finally enables lz4 compression by default at installation time. I thus recommend using an official Proxmox VE ISO image instead of creating an ISO image yourself, although creating your own ISO might still be interesting from an educational point of view or to include fixes that haven’t made it into the official Proxmox ISO yet.

Proxmox VE is a truly great, Debian based Linux distribution to host both KVM virtual machines and OpenVZ containers, using a RedHat based kernel (numlock.ch runs as a KVM guest on Proxmox VE, BTW ;).

With the recent release of Proxmox VE 3.4, the whole package got even better, now also allowing to install Proxmox on top of ZFS (which is the best enterprise file system available to date), specifically its native port for Linux, ZFS on Linux (ZoL).

Unfortunately, Proxmox VE 3.4 doesn’t allow to use lz4 as a compression algorithm at installation time yet: Using lz4 would be strongly recommended however instead of using ZoL’s default lzjb (or much worse: gzip). There are some known workarounds for this, but those are rather tedious, either involving extensive file copying or a manual setup of the ZFS pool and file systems.

The most elegant solution at the moment is creating a bootable ISO image (based on the original bootable Proxmox VE 3.4 ISO image) with a patched /usr/bin/proxinstall script that uses “compression=lz4” instead of “compression=on” by default.

And here’s how to create the patched ISO:

1. Loop-mount the original ISO (can only be mounted read-only):

# mount -o loop /path/to/proxmox-ve_3.4-3f2d890e-1.iso /mnt/cdrom

2. Copy /usr/bin/proxinstall from the mounted ISO image to a read-writeable directory (create directories as necessary):

# cp -a /mnt/cdrom/usr/bin/proxinstall /mnt/cdrom_patched/usr/bin/proxinstall

3. Edit the /mnt/cdrom_patched/usr/bin/proxinstall script as follows:

# diff -u ../cdrom/usr/bin/proxinstall usr/bin/proxinstall 
--- ../cdrom/usr/bin/proxinstall	2015-02-12 17:52:50.000000000 +0100
+++ usr/bin/proxinstall	2015-03-17 21:50:07.662031284 +0100
@@ -592,7 +592,7 @@
     # disable atime during insatll
     syscmd ("zfs set atime=off $zfspoolname") == 0 ||
 	die "unable to set zfs properties\n";
-    syscmd ("zfs set compression=on $zfspoolname") == 0 ||
+    syscmd ("zfs set compression=lz4 $zfspoolname") == 0 ||
 	die "unable to set zfs properties\n";
 }

4. Use the complicated but very powerful tool xorriso (install it, if necessary) to create a bootable ISO image based on the original ISO, but with /usr/bin/proxinstall “overwritten” with the edited proxinstall script:

# xorriso -boot_image grub patch -indev proxmox-ve_3.4-3f2d890e-1.iso -overwrite on -outdev proxmox-ve_3.4-3f2d890e-1-with-lz4-patch.iso -blank as_needed -pathspecs on -add /usr/bin/proxinstall=/mnt/cdrom_patched/usr/bin/proxinstall -- -commit

5. Use this patched ISO to install Proxmox VE 3.4 as usual

After rebooting the installed Proxmox VE 3.4 host/server, use the following command to verify that lz4 has been used by default:

# zfs get compression
NAME              PROPERTY     VALUE     SOURCE
rpool             compression  lz4       local
rpool/ROOT        compression  lz4       inherited from rpool
rpool/ROOT/pve-1  compression  lz4       inherited from rpool
rpool/swap        compression  lz4       inherited from rpool


For your convenience, here’s a patched ISO of Proxmox VE 3.4 for download (Note: Use it at your own risk!)

proxmox-ve_3.4-3f2d890e-1-with-lz4-patch.iso_.gz (571 MB, md5sum: 2abba5445133c011aadb1808237202b0)

Download it, gunzip it and rename it to proxmox-ve_3.4-3f2d890e-1-with-lz4-patch.iso to get rid of the silly underscore (“_”) WordPress appended when I uploaded the file. The resulting ISO image will be 725 MB, md5sum: e09e5d250d16fa182129c72be88a5aa2.

EDIT 20150607: Meanwhile, this fix has been included by Proxmox – the current official Proxmox VE 3.4 Installer ISO finally enables lz4 compression by default at installation time. I thus recommend using an official Proxmox VE ISO image instead of creating an ISO yourself.

Have fun!

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Wi-Fi troubles with a B&W Zeppelin Air and AirPort Extreme/AirPort Time Capsule?

Recently, my B&W Zeppelin Air speakers have started to show a weird problem: I managed to stream music via AirPlay to them, but they would only play the music for a few seconds, then stop for a seemingly random amount of time, then play the music for a second or so again, then stop again, and so on. A lengthy stuttering, so to say.

Turns out, the reason for these troubles was that I set the AirPort Time Capsule’s main SSID wireless security to “WPA2 Personal” and the guest SSID’s wireless security to “WPA/WPA2 Personal”. Now I’ve set them both to “WPA/WPA2 Personal” and the Zeppelin Air works great again! Streaming also works fine if both “networks” are set to “WPA2 Personal” (which is a somewhat safer setting than WPA/WPA2 mixed mode, some old Wi-Fi cards might not work anymore, however).

I can’t quite explain this, based on the observed symptoms (one would expect things to either work or not work, but not half-way). It seems the AirPort Extreme/Time Capsule has troubles using different wireless security protocols for the main network and the guest network. This might also partly explain the generally shaky Wi-Fi connectivity I’ve experienced since upgrading my Macs to Yosemite – the random Wi-Fi connectivity drops even kept occurring in 10.10.2. I’ll keep an eye on it.