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: #!/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 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 #!/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 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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