[Linux]Reboot required?

Doing updates on your Ubuntu installation sometime results in a recommended reboot(for example installing a new kernel). But how do we check if a reboot is required(if you have no access to a GUI or running Ubuntu server)?

Learn in OOP in the most amusing way.

Having issues trying to understand all that weird concepts when it comes to OOP? Fear(!) not! This is probably the most funny and educating paper I have seen when it comes to approaching OOP.

Dont Fear The OOP.pfd

[Linux] Debugging Bash scripts.

Not a fun but still a necessary task when it comes to bash scripting.

Debugging the entire script:

bash -x myScript.sh

Debugging parts of script:

    set -x : activate debugging.
    set +x : stop debugging.

Example:

#!/bin/bash

echo "Simple example script\n"

set -x
for i in $(seq 3)
do
   echo "Hello World!"
done

set +x
echo "Done debugging!"

exit 0

Alternative:

Replace the shebang with following:

#!/bin/bash -xv

 

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.
--Brian Kernighan

[Linux] Create a random password.

cat /dev/urandom | tr -dc 'a-z0-9' | fold -w 10 | head -n 1

tr=type of characters
fold=length of password

[Linux] Simple sync/backup script.

Just polished my backup script including wake on lan. Just a simple script, but still essential to me.

#!/bin/bash

#function for syncing folders

function sync {

rsync -avrz /folders/to/sync user@host:/destination/folder

rsync -avrx /var/www/data/ ~/Dropbox/wiki/ #makes my wiki pages accessible remotely

}

#function for shutdown remote host, remember to change the rights for the poweroff command(eg. chmod u+s(Set the suid bit) poweroff)

function shutdown {

ssh user@host "poweroff"

}

#wol function, requires the wakeonlan package(on Ubuntu, apt-get install wakeonlan). Or you could use my python script(link).

function wol {

wakeonlan macaddress

}

#check if host is up(my rules: if server is up, only sync. If down start server, sync and then shutdown.

if ping -c 3 host

then

        sync

else

        wol

sync

shutdown

fi

exit 0

Note: Since we are using SSH for remote access it's a good idea to setup SSH login without password, follow this link

Note2: This is added to the crontab for automatic execution once a day.

Note3: I'm using hostname lookup instead of ip(which is assigned by my routers dhcp). This means that if my router suddenly changes the assigned ip(I know it's possible to reserve ip) the script is none dependend on ip. Use avahi-daemon and avahi-autoipd for this feature.

Books - Android Development.

I'm currently struggling to learn the Android Platform. Besides from following my absolutely favorite  The New Boston tutorials I also picked up this excellent book:

Beginning Android Application Development (Wrox Programmer to Programmer)

This usually my learning strategy, always use multiple sources.

strace - A very powerful troubleshooting tool for all Linux users.

Interesting article regarding strace