Postgres Recovery

Postgres killed itself during a disk failure and while later trying to start it up I got messages along the lines of:

database system was interrupted; last known up at ...
database system was not properly shut down; automatic recovery in progress
redo starts at 309/3BA1EB48
record with zero length at 309/3C9F8ED8
redo done at 309/3C9F8EA8
last completed transaction was at log time ....
could not fdatasync log file 777, segment 60: Input/output error
startup process (PID 23142) was terminated by signal 6: Aborted
aborting startup due to startup process failure

On further investigation it sound like the transaction log was corrupted. This can be fixed with pg_resetxlog. This will clear the write ahead log and may result in some data loss or loss of integrity but when nothing else works it's a lifesaver. The documentation describes some follow up steps to ensure the integrity of data after postgres is starting properly.

You can do a dry run:
sudo -u postgres /usr/lib/postgresql/8.4/bin/pg_resetxlog -n /var/lib/postgresql/8.4/main
and if that indicates a new segment and there's no other option then you might as well reset with:
sudo -u postgres /usr/lib/postgresql/8.4/bin/pg_resetxlog /var/lib/postgresql/8.4/main
or
sudo -u postgres /usr/lib/postgresql/8.4/bin/pg_resetxlog -f /var/lib/postgresql/8.4/main

Pretty Print XML in Python

From the command line:

python -c "import xml.dom.minidom; xml = xml.dom.minidom.parse('myxmldoc.xml'); print xml.toprettyxml()"

Mounting an encrypted LUKS LVM volume from a live CD

Get Luks and dm-crypt running on the live disk:

sudo apt-get install lvm2 cryptsetup

sudo modprobe dm-crypt

sudo cryptsetup luksOpen /dev/sda4 crypt1

If you LVM setup then you need to continue with:

sudo vgscan --mknodes

sudo vgchange -ay

Take note of the volume group name. 'vg0' in my case.

Mount the disk:

sudo mkdir /mnt/disk

sudo mount /dev/vg0/root /mnt/disk

Adapted rom: http://www.ubuntugeek.com/rescue-an-encrypted-luks-lvm-volume.html

Move Lucid min, max, close buttons to the right

gconftool-2 --set /apps/metacity/general/button_layout --type string menu:minimize,maximize,close

Inotify

Inotify is awesome, I've used the python bindings before to good effect but just today I needed to monitor a directory for whenever a file was created.

Pretty easy:
sudo aptitude install inotify-tools
inotifywait -m -r --format '%f' -e CREATE data/

Clock Screensaver for Ubuntu

You can use the GLText screensaver to display the time whenever you lock your screen:

In the file /usr/share/applications/screensavers/gltext.desktop change

Exec=gltext -root
to
Exec=gltext -root -front -text '%l:%M:%S %p'

ipython and virtualenv

When recently working with virtualenv recently ipython wasn't picking up the correct sites packages directory. Anyhow this post cleared everything up.


In summary...

create ~/.ipython/virtualenv.py
import site
from os import environ
from os.path import join
from sys import version_info

if 'VIRTUAL_ENV' in environ:
    virtual_env = join(environ.get('VIRTUAL_ENV'),
                       'lib',
                       'python%d.%d' % version_info[:2],
                       'site-packages')
    site.addsitedir(virtual_env)
    print 'VIRTUAL_ENV ->', virtual_env
    del virtual_env
del site, environ, join, version_info

add this to ~/.ipython/ipy_user_conf.py
def main():
    execf('~/.ipython/virtualenv.py')