Python for Linux System Administration

Python

for Linux system administration

(yes, this is a commercial)

Vern CederFort Wayne LUGFort 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

perl

combines it all...

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

stringssome built-in string methods

splitstripjoin

replacefindcount

startswithendswith

lowerupperisdigitswapcase

expandtabscenter

encode/decodeformat

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:

#!/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

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 otherprograms 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 morethe os and sys modules

os.environos.getcwdos.chmodos.chown

os.linkos.mkdiros.removeos.rename

sys.argvsys.stdinsys.stdoutsys.stderr

sys.platformsys.exit

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

existsgetmtimeisfileisdirislinkismountsamefilesplit

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#!/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()

daemons

python-daemon

import daemon

from spam import main_program

with daemon.DaemonContext():

main_program

ctypes

load and use C librariesalso works with Windows DLL's

>>> from ctypes import *

>>> libc = CDLL("libc.so.6")

>>> libc.printf("hello %s\n", "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

Quick Python Book, 2nd ed

covering Python 3

due out late this year

http://www.manning.com/ceder

World's largest Python conference

PyCon 2010Feb. 17-25Atlanta, GA

NOW withPoster sessions!

us.pycon.org

Talks

Tutorials

LightningTalks

Keynotes

Open Space

Hands-On Lab

Exhibit Hall

Sprints

Photo: james.rintamakiLicense: 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