Hi,
Programs, even when installed, can only be executed, when
found. Sounds simple, don’t it ?
BUt…
The “but” looks like that:
If – for example – a system related tool like “ldconfig” couldn’t be found (“command not found”), it can have two reasons:
1.) It is really not installed on the system.
2.) It is there but ASH/ZSH/TCSH/SH or what shell ever
did not found it.
For 1.) Install the program yourself. :O)
For 2.)
Type the following
echo $PATH
and you will get a list of paths (seperated by ":"s) where
the shell will search for a command.
Why it is possible, that “suddenly” a command isn’t there
anymore?
1.) You killed the system and have deleted the command.

2,) You have worked as root (you should only do that if
it is absolutely necessary) and now – as user – the
command “has gone”.
Reason: The settings for PATH differ for both accounts.
Why?
There are certain places, where “dangerous” and “system near” commands are installed. Those are most often
/sbin and /usr/sbin.
“ldocnifg” is such an “system near” comand. For checking
try the following:
Type directly (instead of ldconfig)
/sbin/ldconfig and if this does not help
/usr/sbin/ldconfig
if this does not help either, login as root and type
which ldconfig
which gives you the path to ldconfig.
Be careful now. Mistyping can result in a not working
user account! 
Login as user. If bash is your shell (try echo $SHELL)
load $HOME/.bashrc in your favourite editor. Search
for something like
export PATH=…
If found add the path you found for ldconfig to that setting
like that (supposing ldconfig is installed as
/usr/sbin/ldconfig
Before (example !!!)
export PATH=/usr/bin:/bin
After your fix (example!!!)
export PATH=/usr/bin:/bin/:/usr/sbin
after that DONT leave the editor or close the file! Only
SAVE the file.
Start a shell and test, whether everything is working fine.
If so…be happy.
If not…dont worry.
Check the settings again. Every path has to be separated
by ":"s.
What to do if there are no “export PATH=…” thingy there?
You have to do the “My Name is Bond, James Bond”-trick (which is more like a “My Name is Bond, Bond James”-trick 
Add the following line to the end of your .bashrc file:
export PATH="$PATH:/usr/sbin"
(you see, why this is like “My Name is Bond, James Bond” ??? ;O)
Check the setting as shown above.
If eveything works fine, you can leave the editor.
Why is all this a little “dangerous”???
If you add for example (DONT TRY THIS!!!) to you .bashrc
exort PATH=";/urs/bni,/bsin" (mistyping nearly everything)
NO command cannot be found anymore INCLUDING THE
EDITOR TO FIX THAT PROBLEM!.
For this and a lot of other reasons similiar to this it is very
handy to have a KNOPPIX bootable CD on the desktop.
If you shoot the system by mistyping something very badly…DONT WORRY! 
Boot into KNOPPIX (it is a nearly complete Linux environment!) search for the partition, where the file is,
fix the file, leave KNOPPIX, boot the original system and…
TADA! Here we are again !!! 
This has a second good sideeffect: One gets more adventurous and brave in tweaking the system. While you are more tweaking you get a better and deeper knowledge of Linux. Better and deeper knowledge of Linux means: You do lesser mistakes. Makeing lesser mistakes means more success and lesser Boot-Into-KNOPPIX (NOTHING against KNOPPIX!!!). And after all: More fun with Linux means: Lesser feelings of being hated by Linux ;O))
By the way: There are better shells as bash. Look at
zsh. Dont install this fo root, though, since all system
boot scripts are executed under root permissions.
"I tried the linuxfile that used python 2.3, but it just said “segmentation fault”
Sorry, I dont undertand this…what do mean with
“linuxfile” ???
You can find nearly everything for Linux at
www.freshmeat.net (NO, it is NO XXX-site ;O)
Keep hacking! :O)
mcc