Author: LCK (Page 3 of 13)

A physicist on the move...

Git: commit only some of the changes in a file

29 December 2014 / LCK / 1 Comment

If you only want to commit some of the changes to a file in a Git repository, use

git add --patch your_changed_file

This will interactively ask you which lines to keep:

$ git add --patch .emacs
diff --git a/.emacs b/.emacs
index d903495..5a0eb9e 100644
--- a/.emacs
+++ b/.emacs
@@ -69,9 +69,9 @@
 
 ;;; Make better buffer names when opening files with the same name
-(when (autoload 'uniquify "uniquify" "uniquify" t)
+(when (require 'uniquify nil 'noerror)
   (setq uniquify-buffer-name-style 'post-forward-angle-brackets)
-  )
+)
 
Stage this hunk [y,n,q,a,d,/,K,j,J,g,s,e,?]?

Source and more information on StackOverflow.com.

Getting the version of a remote SVN repository via SSH

29 December 2014 / LCK / 0 Comments

A quick note to self: I wanted to find out what Subversion version was run on R-forge, which I access via SSH. This is how to do it:

$ ssh username@svn.r-forge.r-project.org svnserve --version
svnserve, version 1.6.17 (r1128011)
   compiled Nov 20 2011, 01:10:33

Copyright (C) 2000-2009 CollabNet.
Subversion is open source software, see http://subversion.apache.org/
This product includes software developed by CollabNet (http://www.Collab.Net/).

The following repository back-end (FS) modules are available:

* fs_base : Module for working with a Berkeley DB repository.
* fs_fs : Module for working with a plain file (FSFS) repository.

Cyrus SASL authentication is available.

Moving annual backups from an external disk with Ext4 to an external disk with ZFS

28 December 2014 / LCK / 0 Comments

For a few years I have used the Christmas holidays to create a full
backup of my /home on an external hard disk. For that I used a
Bash script around rsync that uses hard links to keep the used disk
space under control. Each backup was saved in a directory named with
the date of the backup. POSIX ACLs were also backed up.

Since last year’s backup I have moved to ZFS (using ZFS on Linux
with Ubuntu 14.04) as filesystem for /home (and others). Since ZFS
makes checksums of data and metadata it has the possibility to
detect corrupted files (and if the data is redundant it can also fix
them). This is a feature I’d like to have for my backups as
well: I’d rather know it when corruption occurs than live in
ignorance.

So the plan is to move the old backups from the external disk to the
ZFS pool in my server. and instead of using hard links I’ll transfer
the backups in order from old to new to the ZFS pool making a
snapshot for each. Additionally I will also turn on compression
(using the lz4 algorithm). Once that is done I will reformat the
external drive and create a ZFS pool called “JaarlijkseBackupPool” on
it (jaarlijks means annual in Dutch).

The old situation

In the current/old situation, this is how much disk space is used
on the external disk (with and without taking the hard links into
account):

$ sudo du -csh /mnt/JaarlijkseBackups/*
102G    /mnt/JaarlijkseBackups/2010-11-28
121G    /mnt/JaarlijkseBackups/2013-02-04
101G    /mnt/JaarlijkseBackups/2013-12-23
324G    total
$ sudo du -clsh /mnt/JaarlijkseBackups/*
102G    /mnt/JaarlijkseBackups/2010-11-28
193G    /mnt/JaarlijkseBackups/2013-02-04
255G    /mnt/JaarlijkseBackups/2013-12-23
549G    total

Copying the data from the Ext4 disk to a temporary ZFS filesystem on my server

The ZFS pool in my server is called storage. In order to save the
POSIX ACLs of the Ext4 system, they need to be enabled when
creating the ZFS filesystem as well. Setting xattr=sa means the
ACLS are stored more efficiently (although this option is not
compatible with other ZFS implementations at this time, so if I
would try to import the ZFS pool in FreeBSD for example, that
information would be inaccessible).

$ zfs create storage/JaarlijkseBackupsOrganized \
      -o compression=lz4 \
      -o acltype=posixacl \
      -o xattr=sa
$ sudo rsync -ahPAXHS --numeric-ids \
     /storage/JaarlijkseBackups/2010-11-28/ \
     /storage/JaarlijkseBackupsOrganized
$ zfs snapshot storage/JaarlijkseBackupsOrganized@2010-11-28

Followed by the same for the same rsync and zfs snapshot
commands for the other two dates.
Once that is finished, this is the status of that ZFS FS:

$ zfs list -r -t all storage/JaarlijkseBackupsOrganized
NAME                                            USED  AVAIL  REFER  MOUNTPOINT
storage/JaarlijkseBackupsOrganized              275G   438G   272G  /storage/JaarlijkseBackupsOrganized
storage/JaarlijkseBackupsOrganized@2010-11-28  1,03G      -  88,9G  -
storage/JaarlijkseBackupsOrganized@2013-02-04  2,33G      -   196G  -
storage/JaarlijkseBackupsOrganized@2013-12-23      0      -   272G  -
$ zfs get -r -t all compressratio storage/JaarlijkseBackupsOrganized
NAME                                           PROPERTY       VALUE  SOURCE
storage/JaarlijkseBackupsOrganized             compressratio  1.13x  -
storage/JaarlijkseBackupsOrganized@2010-11-28  compressratio  1.19x  -
storage/JaarlijkseBackupsOrganized@2013-02-04  compressratio  1.14x  -
storage/JaarlijkseBackupsOrganized@2013-12-23  compressratio  1.12x  -

Partitioning the external disk

The external disk is as 1TB Samsung SATA 3Gbps SpinPoint F2 EcoGreen disk
(type HD103SI, serial number: S1VSJD6ZB02657). The disk uses 512B
sectors:

sudo hdparm -I /dev/sdf |grep Sector
     Logical/Physical Sector size:           512 bytes

Before using it with ZFS, it needs to be partitioned. I used
parted:

$ parted /dev/sdf
GNU Parted 2.3
Using /dev/sdf
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: ATA SAMSUNG HD103SI (scsi)
Disk /dev/sdf: 1000GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  1000GB  1000GB  primary  ext4

(parted) mklabel
New disk label type? gpt
(parted) u
Unit?  [compact]? MB
(parted) p
Model: ATA SAMSUNG HD103SI (scsi)
Disk /dev/sdf: 1000205MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start  End  Size  File system  Name  Flags

(parted) mkpart
Partition name?  []? JaarlijkseBackups-HD103SI-S1VSJD6ZB02657
File system type?  [ext2]? zfs
Start? 1M
End? 1000204M
(parted) p
Model: ATA SAMSUNG HD103SI (scsi)
Disk /dev/sdf: 1000205MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End        Size       File system  Name                                  Flags
 1      1,05MB  1000204MB  1000203MB  ext4         JaarlijkseBackups-HD103SI-S1VSJD6ZB0

(parted) q

This removes the old partition table and creates a new GPT
partition table (which allows naming partitions). Next I set the
units to MB so I can leave 1MB at the beginning and end of the
partition (can be helpful when importing this pool in
e.g. FreeBSD). The disk also shows up in /dev/disk/by=partlabel
now.

Creating the new ZFS pool

$ zpool create -o ashift=9 JaarlijkseBackupPool \
    /dev/disk/by-partlabel/JaarlijkseBackups-HD103SI-S1VSJD6ZB0
$ zpool status JaarlijkseBackupPool
  pool: JaarlijkseBackupPool
 state: ONLINE
  scan: none requested
config:

        NAME                                    STATE     READ WRITE CKSUM
        JaarlijkseBackupPool                    ONLINE       0     0     0
          JaarlijkseBackups-HD103SI-S1VSJD6ZB0  ONLINE       0     0     0

errors: No known data errors

Migrating the data

Now that the new ZFS pool and filesystem are all in place, it is
time to move the backups to the new place, starting with the oldest
backup. The -R option also make sure the attributes like
compression and xattr are transferred to the new FS. The
following commands send each snapshot to the new pool (the -n
option of zfs receive is for doing a dry run, just to show how it
works). After the first snapshot is sent, the other two are sent
using the -i option to zfs send so that only the incremental
differences between the snapshots are sent.

$ zfs send -vR storage/JaarlijkseBackupsOrganized@2010-11-28 | \
      zfs receive -Fvu JaarlijkseBackupPool/oldRsyncBackups
$ zfs send -vR -i storage/JaarlijkseBackupsOrganized@2010-11-28 \
    storage/JaarlijkseBackupsOrganized@2013-02-04 | \
    zfs receive -Fvu JaarlijkseBackupPool/oldRsyncBackups
$ zfs send -vR -i storage/JaarlijkseBackupsOrganized@2013-02-04 \
      storage/JaarlijkseBackupsOrganized@2013-12-23 | \
      zfs receive -Fvu JaarlijkseBackupPool/oldRsyncBackups -n
send from @2013-02-04 to storage/JaarlijkseBackupsOrganized@2013-12-23 estimated size is 84,3G
total estimated size is 84,3G
TIME        SENT   SNAPSHOT
would receive incremental stream of storage/JaarlijkseBackupsOrganized@2013-12-23 into JaarlijkseBackupPool@2013-12-23
14:09:16   4,22M   storage/JaarlijkseBackupsOrganized@2013-12-23
14:09:17   8,46M   storage/JaarlijkseBackupsOrganized@2013-12-23
14:09:18   18,4M   storage/JaarlijkseBackupsOrganized@2013-12-23
14:09:19   24,8M   storage/JaarlijkseBackupsOrganized@2013-12-23
^C
$ zfs send -vR -i  storage/JaarlijkseBackupsOrganized@2013-02-04 \
      storage/JaarlijkseBackupsOrganized@2013-12-23 | \
      zfs receive -Fvu JaarlijkseBackupPool/oldRsyncBackups

Add this year’s backup

At first I tried to add the new backups also to the
oldRsyncBackups FS, but that didn’t work (at least not with an
incremental backup), so I ended up making a new backup. The extra
cost in disk space is not a real problem. Disk space is rather
cheap and the current configuration will last me at least one more
year. So after creating a snapshot called 2014-12-26 of my
/home I ran:

   $ zfs send -v  storage/home@2014-12-26 | \
      zfs receive -Fu JaarlijkseBackupPool/home
$ zfs list -r -t all JaarlijkseBackupPool
NAME                                              USED  AVAIL  REFER  MOUNTPOINT
JaarlijkseBackupPool                              581G   332G    30K  /JaarlijkseBackupPool
JaarlijkseBackupPool/home                         311G   332G   311G  /JaarlijkseBackupPool/home
JaarlijkseBackupPool/home@2014-12-26             51,2M      -   311G  -
JaarlijkseBackupPool/oldRsyncBackups              271G   332G   267G  /JaarlijkseBackupPool/oldRsyncBackups
JaarlijkseBackupPool/oldRsyncBackups@2010-11-28   974M      -  87,1G  -
JaarlijkseBackupPool/oldRsyncBackups@2013-02-04  2,23G      -   193G  -
JaarlijkseBackupPool/oldRsyncBackups@2013-12-23      0      -   267G  -
$ zfs get -r compressratio JaarlijkseBackupPool
NAME                                             PROPERTY       VALUE  SOURCE
JaarlijkseBackupPool                             compressratio  1.15x  -
JaarlijkseBackupPool/home                        compressratio  1.17x  -
JaarlijkseBackupPool/home@2014-12-26             compressratio  1.17x  -
JaarlijkseBackupPool/oldRsyncBackups             compressratio  1.13x  -
JaarlijkseBackupPool/oldRsyncBackups@2010-11-28  compressratio  1.19x  -
JaarlijkseBackupPool/oldRsyncBackups@2013-02-04  compressratio  1.14x  -
JaarlijkseBackupPool/oldRsyncBackups@2013-12-23  compressratio  1.12x  -

Finishing up

In order to be able to disconnect the external drive without
damaging the filesystems use

zpool export JaarlijkseBackupPool

Later, the drive/pool can be imported using the zpool import
command.

Now that the migration is done, the intermediate filesystem
(including the snapshots) can also be removed:

zfs destroy -r storage/JaarlijkseBackupsOrganized

For reference: the old rsync script

#!/bin/sh
#
# Time-stamp: <2013-02-04 16:48:31 (root)>
# This scripts helps me create my annual backups to an external hard
# disk. The script uses rsync's hard link option to make hard links to
# the previous backups for files that haven't changed. It makes the
# backup based on an LVM snapshot it creates of the LV that contains
# the /home partition.
# This script needs to be run as root.
 
today=`date +%F`
olddate="2013-02-04"
 
srcdir="/mnt/backupsrc/"
destdir="/mnt/backupdest/JaarlijkseBackups/$today"
prevdir="/mnt/backupdest/JaarlijkseBackups/$olddate"
 
# LVM options
VG=raid5vg
LV=home
 
# rstnc options
options="-ahPAXHS --numeric-ids"
exclusions="--exclude 'lost+found/'"
#  --exclude '*/.thumbnails'"
# exclusions="$exclusions --exclude '*/.gvfs/'"
# exclusions="$exclusions --exclude '*/.cache/' --exclude '**/Cache'"
# exclusions="$exclusions --exclude '*/.recycle/'"
 
# Check to see if the previous backup directory exists
if [ ! -d $prevdir ]; then
    echo "Error: The directory with the previous back up ($prevdir) doesn't exist" 1>&2
    exit 1
fi
 
# Make a snapshot of the home LV that we can backup
lvcreate -L15G -s -n snap$LV /dev/$VG/$LV
mount /dev/$VG/snap$LV $srcdir
 
 
# Start the backup, first a dry-run, then the full one
rsynccommand="rsync $options $exclusions --link-dest=$prevdir $srcdir $destdir"
 
$rsynccommand -n
 
# Wait for user input
echo "This was a dry run. Press a key to continue with the real stuff or"
echo "hit Ctrl-c to abort."
read dummy
 
$rsynccommand

ProbABEL v0.4.4 released

8 November 2014 / LCK / 0 Comments

It was quite a long time in the making and then a bunch of other stuff came in between, but I finally managed to release v0.4.4 of ProbABEL!

ProbABEL is a toolset for doing fast, memory (RAM) efficient genome-wide regression tests.

This is a bugfix release, but a major one for those who use the Cox proportional hazards regression module. Thanks to some of our users on the GenABEL forum, a serious bug leading to way to many NaN’s in the output was discovered, fixed and tested. This is one of the best examples of community collaboration I have seen in the GenABEL project.

Another bug fixed in this release is one that caused a failed install on MacOS X and FreeBSD. Again a bug reported on the forum by one of our users. Great work!

Uploads to Debian and the Ubuntu PPA are coming ASAP.

Now, let’s get ready for a new feature release, which will include p-value calculation (a long-standing feature request) and major speed-ups (implemented by former colleague Maarten Kooyman). Time to get to work ;-)!

Using rsync to backup a ZFS file system to a remote Synology Diskstation

30 October 2014 / LCK / 1 Comment

Some time ago I moved from using LVM to using ZFS on my home server. This meant I also had to change the backup script I used to make backups on a remote Synology Diskstation. Below is the updated script. I also updated it such that it now needs a single command line argument: the hostname of the Diskstation to backup to (because I now have two Diskstations at different locations). If you want to run this script from cron you should set up key-based SSH login (see also here and here).

#!/bin/bash
#
# This script makes a backup of my home dirs to a Synology DiskStation at
# another location. I use ZFS for my /home, so I make a snapshot first and
# backup from there.
#
# This script requires that the first command line argument is the
# host name of the remote backup server (the Synology NAS). It also
# assumes that the location of the backups is the same on each
# remote backup server.
#
# Time-stamp: <2014-10-27 11:35:39 (L.C. Karssen)>
# This script it licensed under the GNU GPLv3.
 
set -u
 
if [ ${#} -lt 1 ]; then
    echo -n "ERROR: Please specify a host name as first command" 1>&2
    echo " line option" 1>&2
    exit -1
fi
 
###############################
# Some settings
###############################
# Options for the remote (Synology) backup destination
DESTHOST=$1
DESTUSER=root
DESTPATH=/volume1/Backups/
DEST=${DESTUSER}@${DESTHOST}:${DESTPATH}
 
# Options for the client (the data to be backed up)
# ZFS options
ZFS_POOL=storage
ZFS_DATASET=home
ZFS_SNAPSHOT=rsync_snapshot
SNAPDIR="/home/.zfs/snapshot/$ZFS_SNAPSHOT"
 
# Backup source path. Don't forget to have trailing / otherwise
# rsync's --delete option won't work
SRC=${SNAPDIR}/
 
# rsync options
OPTIONS="--delete -azvhHSP --numeric-ids --stats"
OPTIONS="$OPTIONS --timeout=60 --delete-excluded"
OPTIONS="$OPTIONS --skip-compress=gz/jpg/mp[34]/7z/bz2/ace/avi/deb/gpg/iso/jpeg/lz/lzma/lzo/mov/ogg/png/rar/CR2/JPG/MOV"
EXCLUSIONS="--exclude lost+found --exclude .thumbnails --exclude .gvfs"
EXCLUSIONS="$EXCLUSIONS --exclude .cache --exclude Cache"
EXCLUSIONS="$EXCLUSIONS --exclude .local/share/Trash"
EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/tmp/Downloads/*.iso"
EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/.recycle"
EXCLUSIONS="$EXCLUSIONS --exclude _dev_dvb_adapter0_Philips_TDA10023_DVB*"
 
 
 
###############################
# The real work
###############################
 
# Create the ZFS snapshot
if [ -d $SNAPDIR ]; then
    # If the directory exists, another backup process may be running
    echo "Directory $SNAPDIR already exists! Is another backup still running?"
    exit -1
else
    # Let's make snapshots
    zfs snapshot $ZFS_POOL/$ZFS_DATASET@$ZFS_SNAPSHOT
fi
 
 
# Do the actual backup
rsync -e 'ssh' $OPTIONS $EXCLUSIONS $SRC $DEST
 
# Remove the ZFS snapshot
if [ -d $SNAPDIR ]; then
    zfs destroy $ZFS_POOL/$ZFS_DATASET@$ZFS_SNAPSHOT
else
    echo "$SNAPDIR does not exist!" 1>&2
    exit 2
fi
 
exit 0

#!/bin/bash # # This script makes a backup of my home dirs to a Synology DiskStation at # another location. I use ZFS for my /home, so I make a snapshot first and # backup from there. # # This script requires that the first command line argument is the # host name of the remote backup server (the Synology NAS). It also # assumes that the location of the backups is the same on each # remote backup server. # # Time-stamp: <2014-10-27 11:35:39 (L.C. Karssen)> # This script it licensed under the GNU GPLv3. set -u if [ ${#} -lt 1 ]; then echo -n "ERROR: Please specify a host name as first command" 1>&2 echo " line option" 1>&2 exit -1 fi ############################### # Some settings ############################### # Options for the remote (Synology) backup destination DESTHOST=$1 DESTUSER=root DESTPATH=/volume1/Backups/ DEST=${DESTUSER}@${DESTHOST}:${DESTPATH} # Options for the client (the data to be backed up) # ZFS options ZFS_POOL=storage ZFS_DATASET=home ZFS_SNAPSHOT=rsync_snapshot SNAPDIR="/home/.zfs/snapshot/$ZFS_SNAPSHOT" # Backup source path. Don't forget to have trailing / otherwise # rsync's --delete option won't work SRC=${SNAPDIR}/ # rsync options OPTIONS="--delete -azvhHSP --numeric-ids --stats" OPTIONS="$OPTIONS --timeout=60 --delete-excluded" OPTIONS="$OPTIONS --skip-compress=gz/jpg/mp[34]/7z/bz2/ace/avi/deb/gpg/iso/jpeg/lz/lzma/lzo/mov/ogg/png/rar/CR2/JPG/MOV" EXCLUSIONS="--exclude lost+found --exclude .thumbnails --exclude .gvfs" EXCLUSIONS="$EXCLUSIONS --exclude .cache --exclude Cache" EXCLUSIONS="$EXCLUSIONS --exclude .local/share/Trash" EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/tmp/Downloads/*.iso" EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/.recycle" EXCLUSIONS="$EXCLUSIONS --exclude _dev_dvb_adapter0_Philips_TDA10023_DVB*" ############################### # The real work ############################### # Create the ZFS snapshot if [ -d $SNAPDIR ]; then # If the directory exists, another backup process may be running echo "Directory $SNAPDIR already exists! Is another backup still running?" exit -1 else # Let's make snapshots zfs snapshot $ZFS_POOL/$ZFS_DATASET@$ZFS_SNAPSHOT fi # Do the actual backup rsync -e 'ssh' $OPTIONS $EXCLUSIONS $SRC $DEST # Remove the ZFS snapshot if [ -d $SNAPDIR ]; then zfs destroy $ZFS_POOL/$ZFS_DATASET@$ZFS_SNAPSHOT else echo "$SNAPDIR does not exist!" 1>&2 exit 2 fi exit 0

Multiple accounts on an SSH server: managing key files

30 October 2014 / LCK / 0 Comments

I’ve got several domains hosted at the same hosting company, and the company provides SSH access for each of them with a different user name, but with the same SSH server address. As I’m using key-based login to the server (see also my post here) I ran into the following problem: How do I set up my SSH config file such that it knows which key to use for which user name?

It turns out that the solution is easy (thanks Kelvin!): if you use the %r variable in the ~/.ssh/config file it contains the user name which you used when logging in. Similarly, the %h contains the host name you used on the command line. So all I needed to do was to create entries like this:

Host ssh.myhoster.com
     IdentityFile ~/.ssh/hosting-%r.key

and make sure that the corresponding key files are named hosting-domain1.key, hosting-domain2.key, etc. and then log in using a command like ssh domain1@ssh.myhoster.com.

Hiding columns in LaTeX export of org-mode tables

1 October 2014 / LCK / 1 Comment

Today I was working on an Emacs org-mode document that I wanted to export to PDF. The document contained several tables and for the PDF export I wanted to hide one of the columns in the table. Of course I could have removed the column in the org source, but since I might need it in the future that wasn’t really an option.

Searching the internet I came across this e-mail discussion on the org-mode mailing list, where radio tables were suggested. I briefly tried to get that working, but it seems that this is more of an option if you are working in e.g. a LaTeX document and want to use org-style formatted tables.

So I tried another search, this time on how to hide columns in LaTeX, having the idea in mind that I could then use that to fix the org-mode export. Thanks to question on tex.stackexchange.com I came up with the followin solution:

First add the following lines at the top of the org file, after the regular org-mode header (if you have one):

#+LATEX_HEADER: \usepackage{array}
#+LATEX_HEADER: \newcolumntype{H}{>{\setbox0=\hbox\bgroup}c<{\egroup}@{}}

This defines a new column type with the name H (for ‘hidden’). Next, just before the table, simply add an #+ATTR_LATEX: attribute (see the org-mode manual):

#+ATTR_LATEX: :align lHl
| col 1 | to be hidden | col3   |
|-------+--------------+--------|
|     1 | secret       | info 1 |
|     2 | private      | info 2 |
|     3 | hidden       | info 3 |

When you export this to PDF (via C-c C-e lo) the table in the PDF only contains the first and last column.

SSH with several keys: fix “Too many authentication failures” error

17 September 2014 / LCK / 1 Comment

Yesterday I created an SSH key for a new machine. Today I try to log in to a different machine, one that actually doesn’t use keys, and I got the error mentioned in the title. It turns out SSH offers all available keys by default, so I ran out of login attempts before I noticed it.

The solution is simple: Add

IdentitiesOnly yes

to your ~/.ssh/config file.

A more detailed explanation can be found here.

Fixing the crackling noise when turning the volume knob of an old amplifier

16 September 2014 / LCK / 0 Comments

Last weekend I dragged an old JVC A-G90 amplifier from the attic to my study/work room. I was planning on putting it on sale, but while playing with it I decided to connect my computer to it and see whether it could replace my Logitech Z-680 (see below). A quick inventory of my computer use showed me that I didn’t really need 5.1 sound, so going to stereo wouldn’t be a big loss.

So, I hooked up the amplifier to the PC and a set of Klipsch RB-51 bookshelf speakers for a test. It was great! The only downside were the crackling noises I heard when turning the volume knob. These were one of the reasons why it ended up in the attic anyway. I seem to remember that, several years ago, I used a bit of contact spray to fix this issue. For a while. A bit of internet searching led me to the following hint: “Just turn the amplifier off and turn the knob for 20 to 100 times, this usually makes the crackling noise go away, since it is usually caused by dust in the pot meter”. And it worked!

So now I have a good-working amp and excellent sound (I found another set of Klipsch RB-51’s on sale), even at low volumes. Much better than with the Z-680. I also dug up the JVC KD-WR90 cassette player and the JVC T-E50L tuner, as well as the (not matching because too wide) JVC XL-V231 CD player, so now the old stereo set that I know from my childhood is restored in all its glory :-).

What I should do, of course, is compare this amp to the Marantz NR-1601 and SR-6006 I own as well. Just to see how they compare. Maybe something for a cold winter evening.

P.S. Speaker placement

One note about speaker placement: the speakers are very close to me (i.e. less than 1 meter). At first I placed the right speaker at ear level and the left one 15 cm lower. It seemed that the left speaker had lost most of its high-frequency spectrum. Only after raising it to the same height did I get proper balanced sound. Maybe this specific to the Klipsch speakers with their horn tweeter, maybe not. Anyway, something to keep in mind!

P.P.S. The Z-680 hiss problem

The problem with the Z-680 was that it has a low level of hiss/noise coming from the speakers. The hiss wasn’t noticeable when playing games or listening to music, but when the speakers were idle the noise was very noticeable and distracting. Even when the set was muted it was present. This turns out to be an unfixable problem (there was a partial fix with a firmware update) and several discussion threads about it can be found on the internet.

When I used the set in a home theatre setup I never noticed the hiss, but ever since I used it as my computer speaker set (i.e. sitting closer to the speakers), it annoyed me greatly. Even more so since I started working from home, most of the time sitting behind the computer without music, but still with the speakers on in order to notice e.g. Skype calls coming in.

Richard Stallman’s Free Software TEDx talk

11 September 2014 / LCK / 0 Comments

If you’re interested in a short (14 minute) talk on what Free Foftware is all about, have a look at Richard Stallman’s TEDx Geneva presentation. It’s an excellent introduction by the master himself!

Note: the video above is only half the size of the original because I wanted it to fit the width of this blog.

Author: LCK (Page 3 of 13)

Git: commit only some of the changes in a file

Getting the version of a remote SVN repository via SSH

Moving annual backups from an external disk with Ext4 to an external disk with ZFS

The old situation

Copying the data from the Ext4 disk to a temporary ZFS filesystem on my server

Partitioning the external disk

Creating the new ZFS pool

Migrating the data

Add this year’s backup

Finishing up

For reference: the old rsync script

ProbABEL v0.4.4 released

Using rsync to backup a ZFS file system to a remote Synology Diskstation

Multiple accounts on an SSH server: managing key files

Hiding columns in LaTeX export of org-mode tables

SSH with several keys: fix “Too many authentication failures” error

Fixing the crackling noise when turning the volume knob of an old amplifier

P.S. Speaker placement

P.P.S. The Z-680 hiss problem

Richard Stallman’s Free Software TEDx talk

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The old situation

Copying the data from the Ext4 disk to a temporary ZFS filesystem on my server

Partitioning the external disk

Creating the new ZFS pool

Migrating the data

Add this year’s backup

Finishing up

For reference: the old rsync script

P.S. Speaker placement

P.P.S. The Z-680 hiss problem

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Categories

Meta

Archives