This is more of a note to myself, as it’s an error I keep bumping into. When compiling manually using gcc (or g++) you should pass all the libraries you’re compiling against at the end of the argument list. E.g.:
g++ -Wall -lboost_thread my_file.cpp
will result in error like:
undefined reference to `boost::thread::join()'
undefined reference to `boost::thread::~thread()'
while
g++ -Wall vortex5_brute.cpp -lboost_thread
works fine.
Say you’ve got a document with a bunch of exercises and few lemmas. You may want the exercises numbered separately from the numbering of the lemmas and theorem, unlike LyX’s default behavior. This can be achieved by redefining xca, the environment LyX uses for exercises. Add the following to your LaTeX preamble:
\let\xca\@undefined
\theoremstyle{plain}
\newtheorem{xca}{\protect\exercisename}
LyX will still display the incorrect numbering, but the output will be correct nonetheless. The first line, undefines the LyX’s definition of xca, then we set the style to match the old one and we redefine xca, this time without a reference to the theorems’ counter.
After looking for a builtin expectation symbol in LaTeX, and coming up with none, I’ve defined one. Just add:
% Expectation symbol
\DeclareMathOperator*{\E}{\mathbb{E}}
to your LaTeX preamble and you’re done. You’ll also need to add \usepackage{amsmath} or in LyX to tick “Use AMS math package” under Document->Settings->Math Options.
Using the starred version of \DeclareMathOperator makes sure subscripts goes beneath the symbol in display mode.
Variant Whitespace is a nice minimalistic template by Andreas Viklund.
Andreas chose to put the sidebar above the content, which I prefer not to do. Furthermore as the sidebar was a “float” that came before the content, it caused additional inconveniences. E.g. if you had an element with clear: both it would be pushed bellow the sidebar. I’ve patched it a bit in order to fix those issues. You can find my modified version here: variant-whitespace.tar.gz
I came across the following error message
Author: (no author) not defined in authors file
when I tried to import an SVN repository (Open Yahtzee‘s) to Git using git svn and I specified an authors file (using -A). Indeed, the first commit to the svn (which was done using cvs2svn) had no username for the commiter. Apperantly the workaround is to add the following line to your author file.
(no author) = no_author <no_author@no_author>
I tried also doing the same without an email address, but it just didn’t work. It seems Git requires that all authors have an email address.
I like the idea of hashapass, but I’m unwilling to use an online tool, as I fear that someday it might be compromised. So I wrote down my own variant of hashapass. It uses slightly longer passwords, and sha256 as the hash function.
#! /usr/bin/python
"""
passha.py - Generate passwords from a master password and a parameter.
Based on hashapass (http://hashapass.com)
"""
import hmac
import hashlib
def main(passwd, param):
hm = hmac.HMAC(passwd, param, hashlib.sha256)
print hm.digest().encode("base64")[:10]
if __name__=="__main__":
import getpass
passwd = getpass.getpass()
param = raw_input("Parameter: ")
main(passwd, param)
My brother asked me to repair his boot loader, after he accidentally erased his MBR. This can be done easily via LiveCD and the command line.
Boot the system using a LiveCD (I’ve used Ubuntu from USB stick) and do the following:
$ sudo mount /dev/sda /mnt
$ sudo mount --bind /usr/sbin /mnt/usr/sbin
$ sudo mount --bind /usr/lib /mnt/usr/lib
$ sudo mount --bind /dev/ /mnt/dev
$ sudo chroot /mnt
# grub-install /dev/sda
I hope it will be useful for others as well, as the Ubuntu community documentations offers a solution based on Boot-Repair, which seems an overkill for me.
This tutorial will hopefully guide you in making automated encrypted backups to Amazon’s S3 using duplicity. It was written as a followup for Using Duplicity and Amazon S3 – Notes and Examples, in order to organize all the necessary information into a simple tutorial.
Will start by creating a simple wrapper to duplicity:
#! /usr/bin/python
import sys
import os
duplicity_bin = '/usr/bin/duplicity'
env = {
'AWS_ACCESS_KEY_ID': 'PUT YOUR KEY ID HERE',
'AWS_SECRET_ACCESS_KEY': 'PUT YOUR SECRET ACCESS KEY HERE',
'PASSPHRASE': 'PUT ENCRYPTION PASSPHRASE',
}
env.update(os.environ)
os.execve(duplicity_bin, sys.argv, env)
save this under dupicity-wrapper.py and chmod 0500 it so only you will be able to read and execute it.
Note: You’ll want to write down the passphrase and store it in a safe location (preferably in two separate locations). So in case you’ll need to restore the backups, you won’t have useless encrypted files.
Now edit your crontab and add a line like the following:
10 1 * * 0 /path/to/duplicity-wrapper.py /path/to/folder/ s3+http://bucket-name/somefolder &>> ~/log/backups.log
This will create a weekly backup for /path/to/folder. The backup will be encrypted with what ever passphrase you’ve given in the duplicity-wrapper.py. The output of the backup process will be saved into ~/log/backups.log.
You should also run
/path/to/duplicity-wrapper.py full /path/to/folder/ s3+http://bucket-name/somefolder
in order to create full backups. You might want to periodically verify your backups:
/path/to/duplicity-wrapper.py collection-status s3+http://bucket-name/somefolder
/path/to/duplicity-wrapper.py verify s3+http://bucket-name/somefolder /path/to/folder/
To check the status of the backups and to verify them.
And last but not least, in case you ever need the backups, you can restore them using:
/path/to/duplicity-wrapper.py restore s3+http://bucket-name/somefolder /path/to/folder/
As I know, some people will comment on the saving of the encryption passphrase plainly in a file, I will explain my reasoning. I use the above encryption in order to secure my files in case of data leakage from Amazon S3. In order to read my backups, or silently temper with them, some on will have to get the passphrase from my machine. While, this isn’t impossible, I will say it’s unlikely. Furthermore, if someone has access allowing him to read files from my computer, he doesn’t need the backups, he can access the files directly.
I’ve given some thought about making the backups more secure, but it seems you always have to compromise on either automation or incremental backups. But, as I wrote, the current solution seems to me strong enough given the circumstances. Nonetheless, if you’ve got a better solution it would be nice to hear.
In older versions of KDE, Kontact used to keep it’s data in portable formats. iCalendar files for KOrganizer and vCard for KAddressBook. But sometime ago Kontact moved to akonadi, a more sophisticated backend storage. By default (at least on my machine) Akonadi uses MySQL (with InnoDB) as the perssistent storage. I didn’t consider it thourghly when moving my data to Gnome, and I got stuck with the data.
To make things worth, somewhere along the update to KDE 4.6, I got some of the data moved to ~/.akonadi.old. Being stuck with the InnoDB tables, I tried the following solutions without much success:
~/.akonadi folder, contained nothing interesting and Suse’s KDE 4.6 refused to load the data ~/.akonadi.old after I renamed it.
So being upset about Akonadi I did some greping and found strings from my contacts and todo lists in the following files:
Binary file .local/share/akonadi.old/db_data/ibdata1 matches
Binary file .local/share/akonadi.old/db_data/akonadi/parttable.ibd matches
Binary file .local/share/akonadi.old/db_data/ib_logfile0 matches
I opened the files with vim, and found out the contained vCards and iCalendar blobs in them. So instead of directly storing them on the file-system, where they are easily accessible, they are stored in the DB files. I figured it would be easiest to just extract the data from the binary files. I’ve used the following script:
import sys
START_DELIM = "BEGIN:VCALENDAR"
END_DELIM = "END:VCALENDAR"
def main():
bin_data = sys.stdin.read()
vcards = []
start = bin_data.find(START_DELIM)
while start > -1:
end = bin_data.find(END_DELIM,start+1)
vcards.append(bin_data[start:end + len(END_DELIM)])
start = bin_data.find(START_DELIM, end+1)
print "\n".join(vcards)
if __name__=="__main__":
main()
It reads binary files from stdin and outputs iCalendar data that is embedded in it. If you change START_DELIM and END_DELIM to VCARD instead of VCALENDAR, it will extract the contacts’ data.
This migration, had me thinking how important it is that application’s data should be easily portable. It’s a thing, I feel not many projects have high enough on their priorities.
I’ve decided to try Gnome on a new machine that I’ve got, and as part of the move I’ve switched to Evolution (from Kontact). I had some contacts stored in a spreadsheet which I’ve tried to import as CSV to Evolution.
Apparently, unlike Kontact, Evolution won’t ask you what every column means. It would just assume that the CSV is in some weird scheme. If you try to import the CSV, it would force the scheme on you CSV even if it looks completely different. The result – a complete mess of the fields in each contact.
I didn’t find the reference for how Evolution expects its CSVs to look like, and I didn’t want to analyse that either. So finally, I’ve set up a virtual machine, loaded it with OpenSuse KDE live cd and imported the CSV into Kontact and exported it as VCard which I imported to Evolution.
I believe, that the current CSV import in Evolution, just causes user frustration, as it doesn’t act as expected.
Other weird problems I’ve encountered in Evolution which I didn’t solve yet:
If you know how to solve these issues I would really like to hear.