# A numbered environment for example sentences

I want an environment for example sentences where sentences are numbered and can be referenced. This is common in publications in the area of linguistics and there are a few packages that do the trick. But here is my own.

First, we need a counter that provides the number for the sentence:

\newcounter{mySentence}


We reset sentence counter for each chapter:

\@addtoreset{mySentence}{chapter}


We print the sentence number as (chapter.sentence):

\renewcommand*{\themySentence}{(\thechapter.\arabic{mySentence})}


Then we define an environment for one example sentence, where the number will be printed in the beginning of the line and then the sentence follows:

\newcommand{\backskip}{\vspace{-0.4\baselineskip}}
\newenvironment{examplesentence}
{% start env
\backskip%
\stepcounter{mySentence}%
\begin{enumerate} \small%
\renewcommand{\theenumi}{\thechapter.\arabic{mySentence}}%
\renewcommand{\labelenumi}{\themySentence}%
\itemsep0pt \parskip0pt%
\item
}
{% end env
\end{enumerate}
\backskip
}


Next is an environment for more than one example sentence. Here the sentence number will be printed in the beginning of the line and the individual sentences get an a., b., c., in front of them:

\newenvironment{examplesentences}
{% start env
\begin{examplesentence}%
\begin{enumerate} \itemsep0pt \parskip0pt%
\renewcommand{\theenumii}{\alph{enumii}}%
\renewcommand{\labelenumii}{\alph{enumii}.}%
}
{% end env
\end{enumerate}
\end{examplesentence}
}


# Distribute updates from server to pool computers (hacky way)

This is the crowning achievement of my days at the MINT computer pool. Sadly, by the time I write this post, it will all be deleted. So here it is, archived for posterity.

The setting is a typical computer pool setting. 24 computers and one server. All computers load their home directories from the server (see here). Otherwise, each computer is totally independent. The idea is now, that updates to the pool computers can also be distributed from the server. So that I don’t have to sit down at each computer and execute a script which is a real pain. Again, a really common problem and many solutions exist – but I made my own, hacky, one.

Setting up the server side of things is easy. Basically, we create a few folders and put one shell script in the home of a special user called admin. There is a folder /home/admin/poolsetup/script into which we put a script poolupdate.sh. You can get the script from my wkutils github repository. This script goes through all files in another folder, /home/admin/poolsetup/updates, and executes any scripts it finds in there. It redirects the outputs of the execution into a log file in the folder /home/admin/poolsetup/logs. We can use this file to check what happened. And the update script uses the log file to avoid executing scripts twice. If a log file for a given script exists, we don’t execute the script again.

Because the home directories are loaded from the server, each pool computer will have access to files in the home directory of admin. We don’t have to do any copying to distribute the update script to the pool computers and any changes to the script will take effect right away.

So here are the commands for the server setup – basically just create the necessary folder structure with the correct permissions and put the update script there:

mkdir /home/admin/poolsetup/script


On client side, we only have to make the computer execute the update script on a regular basis. We use cron and therefor call crontab which manages the cron jobs:

crontab -e


In the editor, we add these two lines:

00 17 * * 5 bash /home/admin/poolsetup/script/poolupdate.sh
@reboot bash -c "while [[ ! -d /home/admin/ ]] ; do sleep 5; done" ; bash /home/admin/poolsetup/script/poolupdate.sh


The first line will execute the update script every Friday at 5 PM. The second line will execute the script at every system start. We need the ugly loop with the sleep to ensure that the home directories have been mounted, before trying to access them.

So how does making an update work now? Write a script that does what you want to do. Put this script into the folder /home/admin/poolsetup/updates. When a pool computer starts up, it will execute the script. After that, look into the log folder and read the corresponding log to see what has happened. When all computers execute the update, usually you need to read only one log file and then check if all other log files have the same size. Done!

# Access a server with an SSH key

Install ssh on the server:

apt-get install openssh-server


Generate a key pair (files id_rsa and id_rsa.pub) with a passphrase:

ssh-keygen


Edit the ssh configuration file:

vi /etc/ssh/sshd_config


In the file, make the following settings:

   PasswordAuthentication no
RSAAuthentication yes
PubkeyAuthentication yes


Add the public key as an authorized key for root that can be used for login:

cat id_rsa.pub >> /root/.ssh/authorized_keys


That’s all for the server!

Now for the client. Copy the key pair into the folder ~/.ssh. Now you should be able to connect with:

ssh -i ~/.ssh/id_rsa root@server


# Regular backup with rsync and cron

This is nothing new, just for me to remember. We use rsync and cron to make a backup of all home directories regularly. There will be a weekly backup that is readily accessible and a zipped monthly backup.

First, we need to install rsync (this is for Ubuntu, replace with the package manager of your choice):

apt-get install rsync


Then we need to create the directories where we want to save the backups. Here I am putting it into /media/backup for no particular reason, use any directory you like.

mkdir /media/backup/weekly
mkdir /media/backup/monthly


Next the command that actually copies the files:

rsync -a --exclude=".*/" --delete /home/ /media/backup/weekly


The command uses rsync, which is the tool for the job. We want to backup the complete folder home with all the directories contained in there. We exclude hidden files (starting with .) to avoid copying .cache and other temporary files. You may want to refine this setting for your case. The option --delete overwrites the files in the target directory /media/backup/weekly. So last week’s data will be overwritten with this week’s data when the backup runs. I’d suggest running this command directly to see what happens before proceeding with the automation.

Now that we know how to copy the data, we just need to execute this command regularly. This is done with cron via this command:

crontab -e


This opens an editor with all cron jobs that are currently set up. Add two lines for the backup:

00 18 * * 5 rsync -a --exclude=".*/" --delete /home/ /media/backup/weekly
00 6 1 * * tar -cjf /media/backup/monthly/monthly_\$(date +%Y%m%d).tar.bz2 /media/backup/weekly/


The numbers in the beginning of each line give the minutes, hours, day, month and day of the week. The rest of each line is the command. The first line copies the data to /media/backup/weekly on every Friday afternoon (at 18:00). So we will always have a backup that is at most a week old. The second line is executed on every first day of the month at 6:00 and copies the data to /media/backup/monthly in a zipped form.

# Load home directories from a server

The setting is the following: I have a pool of 24 computers and about 20 students who need to be able to login at any of the computers and access their data. Basically the normal setup of a computer pool. Of course there are many solutions for this problem (LDAP and so on), but of course it is more fun to create your own solution!

The basic idea is that the home directories are loaded from the server and overwrite the home directories of the clients. The accounts are created directly on each computer, but a user has the same user ID on every computer, so that the mapping of permissions works.

Now for the details. First the server. As a first step, install the NFS server package:

apt-get install nfs-kernel-server


Configure what should be exported. This is done in the file etc/exports:

vi /etc/exports


We want to export the folder /home/ and make it available for all computers in our pool (the subnet 1.22.333.* – of course that’s not the correct IP). So we add this line to the file:

/home/  1.22.333.0/255.255.255.0(rw,async)


We re-read the configuration to let the changes take effect:

exportfs -ra


Now we can check if the correct folder is exported:

exportfs -v


Finally, we create all student accounts on the server. This will also create a home directory for each one. We use fixed user IDs, so for example we will have hans with UID 1010, lisa with UID 1011, kim with UID 1012, and so on.

Now for the clients, where as a first step we need to install the NFS package for the client:

apt-get install nfs-common


Now we could mount the exported folder from the server by hand, but because we want to mount them permanently, we will use the global fstab file for this:

vi /etc/fstab


In this file, insert the following line (where 1.22.333.4 is the server IP):

1.22.333.4:/home/    /home/  nfs     rw,soft 0       0


Restart the computer for the changes to take effect. And finally, again, we need to create all student accounts on each computer and take care to assign the same UID.

# Empty panel in XFCE

XFCE has a very annoying property for new users. When you start the desktop for the first time, it asks whether you want to use the “empty panel” or the “default panel”. Unfortunately, people who are new to Linux (and even some that are not so new) have no idea what the question is asking. What you usually want to click is “default panel”. Clicking on “empty panel” will usually result in unhappy users – the desktop will be completely empty. Nothing there, not even a logout button. Bad luck for the newbie.

So in a pool where I expect most users to know little to nothing about Linux, it may be a good idea to simply remove the question completely. This can be done by copying the default panel to a specific place (why? don’t ask me – but it works):

cp /etc/xdg/xfce4/panel/default.xml /etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml


If the user already clicked ’empty panel’, the above doesn’t work. What you can do is to get the question back by removing a few files:

rm -r ~/.config/xfce4/xfconf
rm -r ~/.config/xfce4/desktop
rm -r ~/.cache/sessions/


# Set German keyboard layout on command line

sed -i 's/XKBLAYOUT="us"/XKBLAYOUT="de"/' /etc/default/keyboard
setupcon --force


The first line makes the necessary changes in the file that is responsible for the global keyboard layout. The second line applies the change to the current console.

# Set default application in Linux on the command line

Set the default application for Java files to Kate and use Evince for pdfs:

echo "text/x-java=kde4-kate.desktop;" >> /usr/share/xfce4/applications/defaults.list
echo "application/pdf=evince.desktop;" >> /usr/share/xfce4/applications/defaults.list


# Bash settings

A few settings to be put into the .bashrc.

Ignore duplicates in history, but do put in comands that start with spaces:

HISTCONTROL=ignoredups # (default: ignoreboth)


Keep a lot of history:

export HISTSIZE=10000  # default: 1000
export HISTFILESIZE=10000  # default: 1000


When the shell exits, append to the history file instead of overwriting it:

shopt -s histappend


Disable the annoying password thingy in KDE:

unset SSH_ASKPASS