(zenity:22981): Gtk-WARNING **: cannot open display:

Sure, I hadn’t specified a display. So I tried setting the DISPLAY explicitly in my ~/.crontab:

* * * * export DISPLAY=:0.0 && /path/to/checklog

but then I got:

No protocol specified

(zenity:24101): Gtk-WARNING **: cannot open display: :0

The same happened when I tried running other X apps, like audacious. A line in ~/.crontab like this:

* * * * * DISPLAY=:0 /usr/bin/audacious

resulted in errors like this:

No protocol specified
/usr/bin/audacious: Unable to open display, exiting.

It turns out I needed to set, in my ~/.bashrc:

xhost local:mpromber > /dev/null

to allow crontab access to my X display. It now works, either using “export DISPLAY=:0.0″ in the ~/.crontab, or alternatively just using

zenity --notification --display=:0.0

in the script that checks for queued mail.

For immediate relief (this will not persist through a reboot):

sudo modprobe -r pcspkr

For permanent relief, edit the file /etc/modprobe.d/blacklist and add the line:

blacklist pcspkr

trash somefile

Unlike just moving files to wherever you trash folder is using mv, trash-cli does all the nice trashy things like keeping information that will let you easily restore the file (which … ahem … you of course do from the trash can GUI). On Ubuntu, it’s easy to get trash-cli via synaptic:

sudo aptitude install trash-cli

Now, if there only were a way to rename the trash can to “trash” or at least “rubbish” instead of the idiotic “wastebasket” that my Xubuntu with GB locale insists on …

In the latest versions of Ubuntu or Xubuntu, you can change the welcome message via the settings menu for “Login Window” (or, at a command line, type “gksudo gdmsetup”). Go to the “local” tab.

However, the custom welcome message is not displayed for a lot of (possibly most or all of) the themes, if you want a themed login window. My guess is that this is because these themes do not display a welcome message at all, period. To work around this, you can manually edit the .xml file of the theme you wish to use. Let’s assume you want to use the “Human” theme for your login screen. Pick that in the gdm setup window. Set your custom welcome message. Now, go to /usr/share/gdm/themes. You will see that this contains folders named after the different themes. You want to change the “Human” theme, so go to that folder. Now, using sudo, edit the file Human.xml. You will see that it contains xml markup, which is similar to hmtl. Add a section that looks like the following (I don’t think it matters where you add it. I added mine after the “ubuntu logo” section and it works fine):

  <!-- Welcome message (added by MP) -->
  <item type="label">
    <pos y="2%" x="2%"/>
    <normal color="#000000" font="Sans 14"/>
    <!-- Stock label for: Welcome to %h -->
    <stock type="welcome-label"/>
  </item>

Of course, you can change the position, color and font; this should be easy to figure out. Save the file. Next time you log out, you will see the custom welcome message that you have defined in the GUI for the gdm settings on your login screen.

?"&"

I still fall from it from time to time. (I think it has to do with my rudimentary knowledge and usage of “&&” for if-statements in bash shell scripts.

Below I just go through “&&” and “&”. Obviously, this also applies to “||” and “|”.

Here’s a little demo to remind me and to demonstrate this to newbies:

> 1==1
[1] TRUE
> 1==1 & 1==2
[1] FALSE
> 1==1 && 1==2
[1] FALSE

So far, so good. Now look what happens if we apply this to vectors:

> 1:3==1:3
[1] TRUE TRUE TRUE
> 1:3==c(1,3,3)
[1]  TRUE FALSE  TRUE
> 1:3==1:3 & 1:3==c(1,3,3)
[1]  TRUE FALSE  TRUE

This is what you probably want in most cases: element-wise comparison. The “&” here compares each element in the vector “TRUE TRUE TRUE” to the corresponding element in “TRUE FALSE TRUE” and returns a “TRUE” each time they match and a “FALSE” if they don’t. Now look what happens if we use “&&”:

> 1:3==1:3 && 1:3==1:3
[1] TRUE
> 1:3==1:3 && 1:3==c(1,3,3)
[1] TRUE

For “&&”, as the R help page says, “The longer form evaluates left to right examining only the first element of each vector.”

This is quite obvious in this example, but it can get confusing when you use a logical operator to index a vector. Watch this:

> x <- 1:5
> x[x<5]
[1] 1 2 3 4
> x[x<5 & x>2]
[1] 3 4

Fine.

> x[x<5 && x>2]
integer(0)

The reason:

> x>2 & x<5
[1] FALSE FALSE  TRUE  TRUE FALSE
> x>2 && x<5
[1] FALSE

So in the first case, R “sees”

> x[c(FALSE,FALSE,TRUE,TRUE,FALSE)]

and in the second case, it sees:

> x[FALSE]

As long as the first element compares with “FALSE”, you’re actually lucky, because the error will be obvious. It’s tricky when “&&” evaluates to “TRUE” when it looks at the first element, because some R functions will recycle input if it is too short, and this can lead to things like:

> x <- 1:10
> y <- c(1,3:11)
> x==y
 [1]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> x[x==1 & y==1]
[1] 1
> x[x==1 && y==1]
 [1]  1  2  3  4  5  6  7  8  9 10

So basically, for logical comparison, stick to “&” unless you know you need “&&”.

By the way, if you want to see the values that are elements of both x an y, use “%in%”:

> x[x%in%y]
[1]  1  3  4  5  6  7  8  9 10
> y[y%in%x]
[1]  1  3  4  5  6  7  8  9 10

But don’t do:

> y[x%in%y]
[1]  1  4  5  6  7  8  9 10 11

This indexes y using the logical vector returned by “x%in%y”, which is of course:

> x%in%y
 [1]  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE

Keybard failure. Press F1 to continue, F2 for setup.

When I was at home, I could just plug in the keyboard and hit F1, but when I was trying to boot the computer remotely through wake-on-LAN, I was out of luck.

Turns out you can disable this in the BIOS (hit F2). On my Dell, it is under the “Standard CMOS features” section. You’ll find “Halt on …”, which was set to “All errors” for me. Switching this to “All but keyboard” disables the boot process checking for keyboard presence.

I really like kpdf, but it cannot rotate pages. It seems that it is no longer actively developed, and that instead okular is kpdf’s successor. However, in Gutsy, if you try installing okular via aptitude, you get a dependency problem that aptitude cannot resovle for you (something about missing the virtual package libpoppler1).

You can work around this by adding the following repository to your /etc/apt/sources.list:

deb http://ppa.launchpad.net/kubuntu-members-kde4/ubuntu gutsy main

then:

sudo aptitude update && sudo aptitude dist-upgrade

This installs quite a few kde things and may reinstall kde apps you might already have installed, such as amarok. It did for me. My guess is the problem is that okular is a kde4 app, and you need some kde4 stuff for it. I haven’t checked whether this breaks any of the other kde apps on your system! (Personally, I don’t care — I do have amarok installed but I’m hardly using it; I’ve grown fond of quodlibet instead).

Then, you can do:

sudo aptitude install okular

This will install a lot of dependencies.

You won’t be able to start okular by just using the command okular in a terminal, but you can find it in the Xfce menu under the “Graphics” applications. However, a

ps -ef | grep okular

while okular is running reveals that it sits at /usr/lib/kde4/bin/okular, so you can add

alias okular="/usr/lib/kde4/bin/okular"

to your ~/.bashrc (or, maybe add /usr/lib/kde4/bin to your PATH).

Since this is not available through aptitude, you have to download the source and compile, it but it’s straightforward if you follow the readme file that comes with the package. Above all, Ubuntu proved great as usual at helping me get the missing dependencies, by automatically suggesting which package I needed to aptitude when I typed a command it didn’t find (curl-config and cmake).

I just had one problem: when I tried to update the mpm database, I got:

mpm --update-db
mpm: error while loading shared libraries: libMiKTeX207-core.so.1: cannot open shared object file: No such file or directory

It turns out the source files were in a different location, and all I had to do was:

sudo ldconfig

Now installing packages is as easy as:

mpm --install=emerald

sudo aptitude install xkbset
xmodmap -e 'keysym Pause Break = Pointer_Button2'
xkbset m
xkbset exp =m

I don’t know yet whether this will persist after a reboot.

You can, however, pick the “Default” mail agent DigiKam’s dropdown. Note that this will not use the mail agent that you’ve set as default in Xubuntu (or Ubuntu) (which sucks — I wish KDE apps would just accept the system defaults for that). You can generally change such settings using …

kcontrol

… and on a real KDE system, you would look for KDE Components → Default Applications → Email Client. Unfortunately, if you’re using Ubuntu or Xubuntu, you’ll notice that you don’t have an item Default Applications. Here’s what worked for me on Xubuntu:

sudo aptitude install kde-systemsettings

Now you’ll find the entry in kcontrol as described above. I’ve just set it to /usr/bin/exo-open, as this always gets translated to the default mail app that I’ve currently set via Preferred Applications in the Xfce Menu (which conveniently has a default for Mutt).