Python for Linux System Administration

Python

for Linux system administration

(yes, this is a commercial)

Vern Ceder
Fort Wayne LUG
Fort Wayne, IN

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)

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

A scripting language should

handle input & output

process text – search, replace,
pattern matching, etc.

traverse filesystems

use system utilities and libraries
(glue)

What's wrong with
bash & perl?

Nothing, really...

bash

is a great glue language

pipes things like a champ

has a ton of utilities
(the whole system, in fact)

awk and sed

handle strings brilliantly

but...

bash is a pain when things
get complex

sed is tricky

perl makes my head hurt

(I always have rather liked awk)

So what about Python?

handles strings well

is a good “glue”

“batteries included” → I/O,
filesystem, etc

large collection of external libs

Python also

is very readable
(and easy to maintain)

is expressive

is easy to grasp

is either OO (or not)

is fun

everyone's doing it

Redhat

Ubuntu

Google

etc, etc, etc...

but...
(there's always a “but”)

regular expressions aren't built-in

not (quite) as common as perl

and let's talk about

the elephant in the room

indentation

yes, Python uses indentation
to organize code

it makes code more readable

it's no weirder than {} or @$%

get over it

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

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

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

doc@paladin:~/work/olf$ ./num_occur.py len < wc.py
3

regular expressions

re module

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

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

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()

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

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

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', [], [])

Modules: os.path

exists
getmtime
isfile
isdir
islink
ismount
samefile
split

command line arguments

sys.argv
list of all arguments

optparse
parsing all types of arguments

returns options and parameters

automatic help

Modules: others

databases – sqlite3 and others

fork

threading

ssh – paramiko
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()

daemons

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

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)

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

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

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

nd
Quick Python Book, 2 ed

covering Python 3

due out late this year
http://www.manning.com/ceder

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

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

Contact info

http://tech.canterburyschool.org/tech/VernCeder

http://www.manning.com/ceder

vceder@gmail.com

Python for Linux System Administration

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