Type Python, Press Enter, What Happens?

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Type Python, Press Enter, What Happens? Asheesh Laroia, Philip James (@asheeshlaroia, @phildini) PyCon 2015

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Who are these guys?

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ python

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paulproteus@vellum:~ $ python Python 2.7.6 (default, Apr 11 2014, 22:59:56) [GCC 4.8.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>>

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ python

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ echo $PATH

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paulproteus@vellum:~ $ echo $PATH /home/paulproteus/bin:/usr/bin:/usr/local/bin:

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paulproteus@vellum:~ $ echo $PATH /home/paulproteus/bin:/usr/bin:/usr/local/bin: paulproteus@vellum:~ $

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paulproteus@vellum:~ $ echo $PATH /home/paulproteus/bin:/usr/bin:/usr/local/bin: paulproteus@vellum:~ $ python

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paulproteus@vellum:~ $ echo $PATH /home/paulproteus/bin:/usr/bin:/usr/local/bin: paulproteus@vellum:~ $ python

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paulproteus@vellum:~ $ echo $PATH /home/paulproteus/bin:/usr/bin:/usr/local/bin: paulproteus@vellum:~ $ python

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ hexdump -C /usr/bin/python

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paulproteus@vellum:~ $ hexdump -C /usr/bin/python 00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............| 00000010 02 00 3e 00 01 00 00 00 55 49 57 00 00 00 00 00 |..>.....UIW.....| 00000020 40 00 00 00 00 00 00 00 08 15 33 00 00 00 00 00 |@.........3.....| 00000030 00 00 00 00 40 00 38 00 09 00 40 00 1c 00 1b 00 |[email protected]...@.....| 00000040 06 00 00 00 05 00 00 00 40 00 00 00 00 00 00 00 |........@.......| 00000050 40 00 40 00 00 00 00 00 40 00 40 00 00 00 00 00 |@.@.....@.@.....| 00000060 f8 01 00 00 00 00 00 00 f8 01 00 00 00 00 00 00 |................| 00000070 08 00 00 00 00 00 00 00 03 00 00 00 04 00 00 00 |................| 00000080 38 02 00 00 00 00 00 00 38 02 40 00 00 00 00 00 |8.......8.@.....| 00000090 38 02 40 00 00 00 00 00 1c 00 00 00 00 00 00 00 |8.@.............|

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ ﬁle /usr/bin/python

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paulproteus@vellum:~ $ ﬁle /usr/bin/python /usr/bin/python: ELF 64-bit LSB executable

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for dir in os.getenv( 'PATH').split(':'): try: os.stat(dir + '/python') return dir except: pass raise CommandNotFound()

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bash pid: 1221

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bash pid: 1221 paulproteus@vellum:~ $

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bash pid: 1221 paulproteus@vellum:~ $ exec python

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python pid: 1221

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python pid: 1221

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python pid: 1221 paulproteus@vellum:~ $

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python pid: 1221 paulproteus@vellum:~ $ [Process completed]

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bash pid: 1221

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bash pid: 1221 fork()

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bash pid: 1221 fork() bash pid: 1222

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bash pid: 1221 fork() bash pid: 1222 exec()

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bash pid: 1221 fork() python pid: 1222 exec()

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ pstree

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paulproteus@vellum:~ $ pstree init─┬ ... ├─cron ... └─sshd─┬─bash───python └─bash───pstree

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Process Creation 1. Find binary in $PATH 2. Fork 3. Exec

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paulproteus@vellum:~ $ python -v

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# installing zipimport hook import zipimport # builtin # installed zipimport hook # /usr/lib/python2.7/site.pyc matches /usr/lib/python2.7/site.py import site # precompiled from /usr/ lib/python2.7/site.pyc # /usr/lib/python2.7/os.pyc matches /usr/lib/python2.7/os.py paulproteus@vellum:~ $ python -v

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bash pid: 1221 fork() python pid: 1222 exec( ‘/usr/bin/python’, [‘python’, ‘-v’] )

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bash pid: 1221 fork() python pid: 1222 argv = [‘python’, ‘-v’] exec( ‘/usr/bin/python’, [‘python’, ‘-v’] )

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python pid: 1222 argv = [‘python’]

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Python 2.7.6 (default, Apr 11 2014, 22:59:56) [GCC 4.8.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>>

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No content

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/dev/pts/3

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python pid: 1222 0: /dev/pts/3

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python pid: 1222 0: /dev/pts/3 stdin

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python pid: 1222 0: /dev/pts/3 2

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python pid: 1222 0: /dev/pts/3 termios 2

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python pid: 1222 0: /dev/pts/3 termios 2

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paulproteus@vellum:~ $

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paulproteus@vellum:~ $ strace python

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paulproteus@vellum:~ $ strace python [...] read(0,

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paulproteus@vellum:~ $ strace python [...] read(0, 2

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paulproteus@vellum:~ $ strace python [...] read(0, “2”, 1) 2

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paulproteus@vellum:~ $ strace python [...] read(0, “2”, 1) read(0, 2

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paulproteus@vellum:~ $ strace python [...] read(0, “2”, 1) read(0, 2 +

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paulproteus@vellum:~ $ strace python [...] read(0, “2”, 1) read(0, “+”, 1) 2 +

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paulproteus@vellum:~ $ strace python [...] read(0, “2”, 1) read(0, “+”, 1) read(0, “2”, 1) read(0, “\n”, 1) 2 + 2 Enter

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while True: line = ‘’ chr = sys.stdin.read(1) line += chr if chr == ‘\n’: print eval(line)

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while True: line = ‘’ chr = sys.stdin.read(1) line += chr if chr == ‘\n’: print eval(line)

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python pid: 1222 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3

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bash pid: 1221 python pid: 1222 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3

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bash pid: 1221 python pid: 1222 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3 foreground

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Special Types of Input

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Ctrl C

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Ctrl C termios

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sigint Ctrl C termios

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python pid: 1222 sigint Ctrl C termios

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>>>

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>>> Crtl C

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>>> Crtl C KeyboardInterrupt >>>

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python pid: 1222 sigint

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python pid: 1222 sigint sig pipe

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cat pid: 1222 0: /dev/pts/3 Ctrl D termios

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cat pid: 1222 0: /dev/pts/3 Ctrl D termios

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python pid: 1222 0: /dev/pts/3 Ctrl D termios

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>>> import sys >>> sys.exit()

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>>> raise SystemExit()

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paulproteus@vellum:~ $ strace python

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paulproteus@vellum:~ $ strace python [...] exit(0

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paulproteus@vellum:~ $ strace python [...] exit(0 paulproteus@vellum:~ $

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paulproteus@vellum:~ $ strace python [...] exit(0 paulproteus@vellum:~ $ echo $?

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paulproteus@vellum:~ $ strace python [...] exit(0 paulproteus@vellum:~ $ echo $? 0

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>>> import sys >>> sys.exit(1)

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>>> import sys >>> sys.exit(1) paulproteus@vellum:~ $ echo $? 1

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bash pid: 1221

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python pid: 1222 argv = [‘python’] bash pid: 1221

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python pid: 1222 argv = [‘python’] 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3 bash pid: 1221

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python pid: 1222 argv = [‘python’] sigint sig pipe 0: /dev/pts/3 1: /dev/pts/3 2: /dev/pts/3 bash pid: 1221

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Be Curious! • pstree • strace • ﬁle/hexdump

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Talks to explore more • Systems Programming as a Swiss Army Knife (Julia Evans, Room 517c, Saturday @1050am)* • Exploring is never boring: understanding CPython without reading the code (Allison Kaptur, Room 710a, Saturday @ 245pm) • Where in your RAM is "python san_diego.py”? (Ying Li, Room 517c, Sunday @ 110pm) • Getting comfortable with web security: A hands-on session (Asheesh Laroia, Jacky Chang, Nicole Zuckerman, Room 512cg, Thursday @ 9am)* • Finding Spammers & Scammers through Rate Tracking with Python & Redis (Mica Swyers, Jay Chan, Room 511, Sunday @ 150pm) Talks by friends *time machine may be required

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Questions? Thanks! Asheesh Laroia, Philip James (@asheeshlaroia, @phildini)