Slides for "Python for Linux System Administration" given at Ohio Linux Fest, Columbus, OH, 09-26-2009

1. Python
for Linux system administration
(yes, this is a commercial)
Vern Ceder
Fort Wayne LUG
Fort Wayne, IN

2. Instead of?
the “official” languages for sysamins
bash* (and awk and sed)
*or your favorite similar shell
perl
(if you don't believe me,
ask O'Reilly)

3. http://www.oreillyschool.com/courses/asac4/

4. A scripting language should
handle input & output
process text – search, replace,
pattern matching, etc.
traverse filesystems
use system utilities and libraries
(glue)

5. What's wrong with
bash & perl?
Nothing, really...

6. bash
is a great glue language
pipes things like a champ
has a ton of utilities
(the whole system, in fact)

7. awk and sed
handle strings brilliantly

8. perl
combines it all...

9. but...
bash is a pain when things
get complex
sed is tricky
perl makes my head hurt
(I always have rather liked awk)

10. So what about Python?
handles strings well
is a good “glue”
“batteries included” → I/O,
filesystem, etc
large collection of external libs

11. Python also
is very readable
(and easy to maintain)
is expressive
is easy to grasp
is either OO (or not)
is fun

12. everyone's doing it
Redhat
Ubuntu
Google
etc, etc, etc...

13. but...
(there's always a “but”)
regular expressions aren't built-in
not (quite) as common as perl

14. and let's talk about
the elephant in the room

15. indentation
yes, Python uses indentation
to organize code
it makes code more readable
it's no weirder than {} or @$%
get over it

16. strings
some built-in string methods
split lower
strip upper
join isdigit
replace swapcase
find expandtabs
count center
startswith encode/decode
endswith format

17. for example
to do what wc does:
#!/usr/bin/env python
import sys
data = sys.stdin.read()
chars = len(data)
words = len(data.split())
lines = len(data.split('n'))
print ("{0} {1} {2}".format(lines, words, chars))
doc@paladin:~/work/olf$ ./wc.py < wc.py
12 22 189

18. or number of occurrences?
in bash (not mine):
doc@pal:~/olf$ tr " " "n" < wc.py | grep len | wc -w
3
in Python:
#!/usr/bin/env python
import sys
data = sys.stdin.read()
print data.count(sys.argv[1])
doc@paladin:~/work/olf$ ./num_occur.py len < wc.py
3

19. regular expressions
re module
syntax similar to perl
import re
>>> re.findall("[Ll]en", "len is the Length")
['len', 'Len']

20. exception handling
y = 10
try:
x = y / 0
except ZeroDivisionError, e:
print e
integer division or modulo by zero

21. glue
multiple ways to call other
programs and pipe the results
sys.stdin, sys.stdout, sys.stderr
os.system(), os.spawnl()
subprocess.call()
subprocess.Popen()

22. Modules: subprocess
from subprocess import *
p = Popen(["ls", "-l"], stdout=PIPE, stderr=PIPE)
out, err = p.communicate()

23. files, directories and more
the os and sys modules
os.environ sys.argv
os.getcwd sys.stdin
os.chmod sys.stdout
os.chown sys.stderr
os.link sys.platform
os.mkdir sys.exit
os.remove
os.rename

24. Modules: os
os.walk()
import os
>>> for x in os.walk('.'):
... print x
...
('.', ['emptydir'], [ 'chinese-python-
poster.jpg', 'olf_proposal.txt', 'wc.py',
'olf.odp', 'shell.png', 'olf.txt',
'Pil.gif', 'adminscripting.png',
'num_occur.py'])
('./emptydir', [], [])

25. Modules: os.path
exists
getmtime
isfile
isdir
islink
ismount
samefile
split

26. command line arguments
sys.argv
list of all arguments
optparse
parsing all types of arguments
returns options and parameters
automatic help

27. Modules: others
databases – sqlite3 and others
fork
threading

28. ssh – paramiko
#!/usr/bin/env python
import paramiko
hostname = 'localhost'
port = 22
username = 'test'
password = 'password'
paramiko.util.log_to_file('paramiko.log')
s = paramiko.SSHClient()
s.load_system_host_keys()
s.connect(hostname, port, username, password)
stdin, stdout, stderr = s.exec_command('ifconfig')
print stdout.read()
s.close()

29. daemons
python-daemon
import daemon
from spam import main_program
with daemon.DaemonContext():
main_program

30. ctypes
load and use C libraries
also works with Windows DLL's
>>> from ctypes import *
>>> libc = CDLL("libc.so.6")
>>> libc.printf("hello %sn", "Python")
hello Python
13
>>> print libc.time(None)
1253757776
>>> import datetime
>>> datetime.datetime.fromtimestamp(libc.time(None))
datetime.datetime(2009, 9, 23, 22, 5, 56)

31. A 2 line HTTP server
from http.server import HTTPServer,
SimpleHTTPRequestHandler
server = HTTPServer(("",8000),
SimpleHTTPRequestHandler)
server.serve_forever()

32. What about Python 3?
it's a better language than 2.x
it's not backward compatible
it's supported by the developers
it's the future
it's not here (for sysadmins) yet

33. ipython, the uber shell
extensive history
usable as a system shell
http://ipython.scipy.org
In [1]: print "hello"
------> print("hello")
hello
In [2]: ls
adminscripting.png olf.odp Pil.gif

34. nd
Quick Python Book, 2 ed
covering Python 3
due out late this year
http://www.manning.com/ceder

35. World's largest Python conference
Talks
PyCon 2010
Open Space
Tutorials
Hands-On Lab
Lightning
Talks Feb. 17-25 Exhibit Hall
Keynotes
Atlanta, GA Sprints
NOW with
Poster sessions!
us.pycon.org
Photo: james.rintamaki
License: Attribution-
Share Alike 2.0
Generic

36. Resources
& contact info
Python for Unix and Linux System Administration,
Noah Gift, Jeremy M. Jones, O'Reilly Media 2008
Pro Python System Administration,
Rytis Sileika, Apress, (not yet published)
“Python for system administrators”, James Knowlton,
IBM DeveloperWorks, 2007
http://www.ibm.com/developerworks/aix/library/au-python/
Python Cookbook, Martelli, Ravenscroft & Ascher,
O'Reilly Media 2005

37. Contact info
http://tech.canterburyschool.org/tech/VernCeder
http://www.manning.com/ceder
vceder@gmail.com