Chris Hood's blog

Xwindows - No Icons on Desktop, No Menus

So you login to your Linux machine using Xwindows, either remotely with some window manager running locally or at the console, and POOF! there are no icons or menus on your desktop.  How are you going to get anything done if you cant start any applications?

Well I don't know what the cause of the problem is, I will assume either X crashed or your last X session was interrupted in some manner, but the actual problem is that X creates a bunch of temporary files in /tmp for your X sessions.

drwx------   3 v683653 gsoc   4096 Mar 28 13:45 gconfd-<userid>
drwx------   2 v683653 gsoc   4096 Mar 28 13:45 keyring-WnN0sX
srwxr-xr-x   1 v683653 gsoc      0 Mar 28 13:45 mapping-<userid>
drwx------   2 v683653 gsoc   4096 Mar 28 13:45 orbit-<userid>
drwx------   2 v683653 gsoc   4096 Mar 28 13:45 ssh-zBclu32077
-rw-------   1 v683653 gsoc   2940 Mar 28 13:45 xses-<userid>.NBYSMy

and it is supposed to destroy these or create new the next time you create an X session.  Well if your X session crashes or is interrupted in some other bad way these files aren't removed.

So simply end your current X session and delete them in any manner you like, I like to do it like this:

rm -r /tmp/*<userid>*

And then try to login to X again, you should see your desktop as normal again.

Charging your Ipod Touch with Linux/

If you have tried to charge your Ipod Touch on linux you have noticed more than likely that your linux machine thinks its a camera, and if you cancel the import wizard (or even if you dont) the battery charging icon goes away and it simply shows your regular Ipod screen and no charging occurs.

So I needed to charge mine with linux, so off to Google I go, well in no time I found Matt Colyers site which pointed me to his kernel module page. 

This started out as a kernel module to get the iPhone to charge in linux and he has added an iPod Touch module as well.

So I downloaded the module, followed the README to compile it.  Then I inserted it into the running module with "insmod ipod_touch.ko" and voila plug in the touch, you will still get the camera import thing but you can just cancel it and it will still charge.

After you compile this module you will need to install to be used on reboot with some form of the steps below, I am using Ubuntu on my laptop and used these steps, they WILL be different for your distribution.

1. Copy the ipod_touch.ko file to /lib/modules/<kernel_version>/extras/
2. As root run "depmod" to rebuild all of the module dependencies that will include your new module.
3. Edit /etc/modules and add "ipod_touch" to a new line at the bottom of the file.  This will load it at startup.
4. Then you can unload the module if you loaded it earlier with "rmmod ipod_touch" and do a "modprobe ipod_touch" with your iPod Touch plugged in and the kernel should load the module and cause your touch to beep and you will get the camera import wizard, just hit cancel and you should still see the charging icon on the touch.

This should get you up and running perfectly, if you have the iPhone get the iPhone module of course and if a touch then get the touch one of course.   Technically you could get the iPhone module and use it for the touch but you would have to make an edit to the source code for it to work, the iPod Touch module, as I understand it, is just the phone module with the change already made.

grep a file for multiple terms

This is a pretty simple thing, but something that I never really thought about looking up.  If you want to search a file for multiple terms and see all the lines with line numbers so you can note that, in the past I might do something like this:       

       <shell>: cat -n geo2.pl |grep 143
        <shell>: 9  $xml = "1439087.gpx";
Which of course would work, but that would only give me one line of output for that one word, and then I would have to do the same thing again for each term I wanted to search for.

With "egrep" you can use multiple terms conditionally with | then you would get all the terms and lines associated in one command like this:

        <shell>: egrep -in "nicolae|apollyon|desecration" leftbehind
        <shell>: 3:nicolae
        <shell>: 5:apollyon
        <shell>: 9:desecration

As you can see I looked for any of those words in that file and got back its existence and on what line it was found.  Could be very handy.
There are TONS of things you can do with egrep it is very powerful so to learn more hit the command line with "man egrep" and RTFM.  :o)

vimdiff - Edit files and show differences

Ok everyone that uses Linux or Unix knows about the command line program called "diff", which takes two files and shows you the differences.  However most people that I know have a hard time figuring out how to read the output, there are little arrows > that come out and you have to remember which files in what order you called them to figure out the arrows.

Well with vimdiff this is much easier, vimdiff will edit two or three versions of a file with Vim and show differences.  Now on the first look at that last sentence you say "that's the same thing diff does", Well not really.

First this will actually just show the files in vim but in a side by side view, with the differences highlighted and the lines that are the same collapsed, like in the pic below:

Vimdiff1

So as you can see this is already a huge improvement, the lines that are different are shown and highlighted and the ones that are the same are collapsed, now you can expand those collapsed portions if you like.

Now for one of the better parts, if you have two configuration files, and you want to see the differences and make changes to one or both of these files, you can do that in vimdiff, because it IS vim after all.  So make your changes and save them with the normal set of vim commands.

If you don't want to make any changes and you want to get out of this you could just do the normal ":q" but that will only close the one your in, but if you do ":qall" it will close both files in both sides of vimdiff and "poof!" your out.

There is also a GUI version of this called "gvimdiff", which behaves in the same manner but in a GUI and you can click on the "+" to expand the hidden lines if you wish.  This looks like the pic below:

Vimdiff2

As you see this is a nice handy GUI and looks basically the same.

I hope this helps someone, I know that I will be adding it to my toolbox.

makewhatis.cron error from redhat linux machines

Ok so if you are seeing an email from cron like the below:

/etc/cron.weekly/makewhatis.cron:

zcat: ./cancel.1.gz: No such file or directory

This is an issue with the cancel-cups man page (/usr/share/man/man1/cancel-cups.1.gz) it is missing from security errata package (cups-1.1.17-13.3.16), but the link (cancel.1.gz) is still created.

This is a very simple thing to fix, simply upgrade your cups package by using up2date cups , this will update your version of cups to something later than the one with the bug.

Math on the command line

There is an application called 'bc', which is an arbitrary precision calculator language.  Check out the man page for it using 'man bc' there are alot of real sophisticated things you can do with this, and since I am not a mathematician I wont even try to explain it.

A basic way to use it would be to do something like the example below:
example: echo 224*42/3 | bc -l
Which would get you the result of 3136.00000000000000000000 , you can see how this might be handy for doing math in shell scripts or just on the fly to find out what 2*2 is.

Anyway read the man page, and I hope this has helped someone, I will be using it because I generally suck at math...hehe ;-)

.vimrc and customization

Okay first this is a total rip off (literaly copied verbatim) from the jmcpherson.org site.  But it is VERY useful and good enough to bookmark, and provide a copy here.  So here goes.

vim is extremely customizable. It will read the file .vimrc in your home directory before it starts. This file can contain settings and even scripts. The below settings are ones I've found helpful -- give them a try!

set nocompatible

This setting prevents vim from emulating the original vi's bugs and limitations.

set autoindent
set smartindent

The first setting tells vim to use "autoindent" (that is, use the current line's indent level to set the indent level of new lines). The second makes vim attempt to intelligently guess the indent level of any new line based on the previous line, assuming the source file is in a C-like language. Combined, they are very useful in writing well-formatted source code.

set tabstop=4
set shiftwidth=4

I prefer 4-space tabs to 8-space tabs. The first setting sets up 4-space tabs, and the second tells vi to use 4 spaces when text is indented (auto or with the manual indent adjustmenters.)

set showmatch

This setting will cause the cursor to very briefly jump to a brace/parenthese/bracket's "match" whenever you type a closing or opening brace/parenthese/bracket. I've had almost no mismatched-punctuation errors since I started using this setting.

set guioptions-=T

I find the toolbar in the GUI version of vim (gvim) to be somewhat useless visual clutter. This option gets rid of the toolbar.

set vb t_vb=

This setting prevents vi from making its annoying beeps when a command doesn't work. Instead, it briefly flashes the screen -- much less annoying.

set ruler

This setting ensures that each window contains a statusline that displays the current cursor position.

set nohls

By default, search matches are highlighted. I find this annoying most of the time. This option turns off search highlighting. You can always turn it back on with :set hls.

set incsearch

With this nifty option, vim will search for text as you enter it. For instance, if you type /bob to search for bob, vi will go to the first "b" after you type the "b," to the first "bo" after you type the "o," and so on. It makes searching much faster, since if you pay attention you never have to enter more than the minimum number of characters to find your target location. Make sure that you press Enter to accept the match after vim finds the location you want.

set virtualedit=all

By default, vim doesn't let the cursor stray beyond the defined text. This setting allows the cursor to freely roam anywhere it likes in command mode. It feels weird at first but is quite useful.

Type :help options within vim to get a complete list of options.

Firefox: This Address is Restricted

I took this from another website, but it worked out for me, and I needed it in order to attach to VNC on a non standard http port.

It seems as a security touch to Firefox it is now blocking non standard HTTP ports. Kinda of annoying really. To override this type this in the address bar "about:config" and search for "network.security.ports.banned.override". This may or may not exist, if it doesn't, right click anywhere in the window and select new->string and use "network.security.ports.banned.override" as the name and the port number you need to connect to as the value. You can also select a range of ports by using "1-1024" as such a value or as a CSV style values such as "1024, 8080, 1-1000, 80"… etc

Using 'watch' to watch a file

If you know that some process is going to update a file every so often you can watch for those changes without just doing a tail -f or constantly cat'ing the file out and looking for a change.

Try this and you will see what I am talking about.
run "watch -n 5 -d tail -1 /var/log/messages"  (of course without the quotes) in a shell.  This will cause the shell display to change and will starting watching the differences of the last line of the file /var/log/messages.

Watch1

Then in another shell type 'logger "blah to me" ' (the quotes around "blah to me" are needed). and watch your first shell to see the differences get highlighted until the next update. The -n is the interval (number) of seconds to update, and the -d (differences) is highlight the differences.

There are plenty of other reasons to use this, I will leave it up to your imagination. Have fun!

Force FSCK at next boot

This is an easy task, simply login as root and touch the file /forcefsck then the next time the machine boots it will force an FSCK.  The example is below:

    Create a file called forcefsck:

    # touch /forcefsck

    Now reboot system:

    # reboot

The machine will reboot and do an FSCK.