Mysterious Processes and Frustrations |
|
|
menu A item 1 item 2 item 3 item 4 item 5 Search this site |
Linux Chronicles, Chapter IV: Mysterious Processes and Frustrations... Well, I want to run something called a cron daemon, which is a Linux way to run certain programs, scripts, or commands once per day at an appointed time.
Or once per week, or once per hour, etc. My desire is to run five Python scripts (don't worry, they were not written by me, I'm much too brain dead ;-)).
The five scripts should, when run properly, automatically search the web for new articles on the Python programming language, and then FTP the new file to my web site each day, giving a new list each day of new web articles about Python. Cool huh? I thought so too...
So I set my crontab file, by creating and editing a my_cron_file and typing crontab my_cron_file; that sets up the cron daemon, just like all the books say to do, or just like the man pages say. (By the way, typing man I am embarrassed to be seeking help
on this subject. I have used crontab to set up a my_cron_file that runs
five Python scripts to automatically run mygale.py and associated programs
to update the output. file listing new web articles about Python once
per day.
My crontab file reads as such:
30 4 * * * /usr/bin/python /home/ron/mygale.py get all
crond is running , as checked using
Also, ps aux | grep cron shows a /usr/sbin/cron
process.
Finally, the cron daemons log check /var/log/cron
shows all 5 Python scripts properly called at their appointed times each
morning. No errors are at all are recorded in the cron error log files.
Now, when I run these scripts exactly as typed above,
from the Bash shell,
The mystery is that, even though the log files show the
Python scripts called each day, no update occurs on my web site . In deed,
when I check the output. file in my /home/ron directory, it is not
updated at all by these cron processes. Even though the log file shows
the scripts as being ran, it is as if they did not run at all, in that
no output occurs.
Yet when I run the same scripts manually, all is updated.
So this morning at 4:30 AM I sat up and ran a "top" process
from the Bash shell, that shows all running processes. Sure enough, at
exactly 4:30 AM, a new Python process was spawned. The new Python process
was matched with a new entry in the cron log file of the mygale.py program
being called.
I watched carefully, and the mygale.py process lasted
for about 30 seconds and then disappeared from the "top" screen. I assume
it terminated normally. Except that when I run the mygale.py get all script
manually in the BASH shell, it takes about two minutes to complete.
This is the only sign of any problem, but still no error messages are generated
anywhere I can find.
Well, it seems to me that a series of processes on Linux
or any operating system should be deterministic. That is, things should
make sense, when the exact same steps are taken, the result should always
be the same.
This procedure I am trying to do does not seem to make
sense to me, it seems mysterious. Linux should not be mysterious.
Can anyone help me?
By the way, shouldn't it be possible to cut and paste
from the BASH shell to a text editor? It would save me a lot of typing
;-))))
The clipboard in general is a frustration; I can't yet
make it work properly in many situations. Is it me or does the KDE clipboard
lack a lot of functionality compared to Windows clipboard? I can't even
copy and paste from K-EDIT, nor K-WORD, to Netscape Composer. Oh, well.
One last frustration: Linux does hang, at least to the
point that this newbie can't recover from it. My box hung when I tried
to open a web presentation by Guido van Rossum about Python Conference
10 using K Presenter. I could not even open a console nor close the
offending KDE shell to get back to a command line. The box also hangs when
I try to print using cups on my HP T45 printer. (I wish I could use my
printer.) My downloaded Open Office also hangs my computer just by trying
to open it.
Nonetheless, these hang-ups and crashes are not of pivotal
importance ot me. But mysterious behavior that not does not allow me to
run daily scripts to update my web site does bother me. Computers shooed
not be mysterious. They should be deterministic. Do a, then b, then c,
get X for output.
Help ;-))))
Ron Stephens
|