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Monday, June 4, 2012

A Basic UNIX Overview



  One of the most common operating systems in existance is Unix. Unix
  exists in many different flavors, from Berkeley BSD to AT&T System V
  to SunOs. Basic working knowledge of Unix is almost essential to a
  hacker, as it is the system a hacker is most likely to come across.
  If you intend to use the internet at all, or to do any serious
  exploration of Telenet, the ability to navigate through Unix is a
  necessity. (Unix is also the single most interesting system in
  existance: it's just fun to fuck with).
  Unix Logins

  Most Unix logins look essentially the same. A general Unix login
  prompt looks something like this:

  connected to

  That first line is the system identifier. Although it's not at all
  essential to what you are doing, it's good to know what system you are
  attempting to log on to.
  The second line is what typically identifies the system you are on as
  Unix. Almost all Unix systems greet a user with the same prompt:
  Well, there's not much to do in Unix from the outside, and Unix
  systems are typically fairly secure at this point. You may be able to
  obtain a list of users, or current users, by logging in as 'who', but
  other than that there are few functions available here.
  Unless you are on the internet, or have accounts specifically for the
  specific machine you are on, the only way on to the system is to try
  the default passwords. What are the default passwords?
  Unix systems come installed with certain passwords automatically. In
  addition, some accounts must exist on a system. One such account is
  'root'. This user is the divine Kami of the Unix system... in short,
  an all access pass. Unfortunately, few systems allow root logins
  remotely, and even fewer leave 'root' unpassworded. Nevertheless, it's
  always worth a shot... try this:

  connected to
  login: root
  password: root
  invalid login

  well, nice try anyways... other possible passwords for root include
  'sysadmin', 'sys', 'admin'... you get the idea. You may also want to
  try these passwords with a single digit appended (added, idiot) to
  them... meaning the password 'root' could be 'root1' or 'root2'.
  An interesting tip about passwords in general... many people that use
  passwords under 8 characters tend to add a digit or a non-alphanumeric
  character to the password. This is done in order to hinder guessing,
  and to stop password breakers (more on this later). In this case, you
  may want to try adding a space before root... or even an ascii 255 to
  the end.
  Fortunately, there is more than one default password in a unix
  system... a quick list:

  sys        sys
  bin        bin
  daemon     daemon
  rje        rje
  setup      setup
  uucp       uucp/nuucp/anonymous
  nuucp      uucp/nuucp/anonymous
  mountfsys  mountfsys

  In the System

  Ok, at this point, I'm going to assume you've gotten past the login...
  as painful as that may sound. Although Unix may be secure from the
  outside, without effort from the system administrators, the inside of
  the system is not.
  First off, you'll likely by asked for a terminal. vt100 serves your
  purposes sufficently, and it's typically the default, so hit enter.
  Now, hopefully, you have a prompt. There are many different types of
  unix prompts, some of which contain current directory information,
  some of which are just a single character. Just don't panic when my
  examples don't look exactly like what you've got on your screen.
  The first thing you *need* to do on the system is establish your tty
  paramters. As eldritch and arcane sounding as this term may seem, it's
  actually quite simple... you need to tell the system what keys are
  going to do what.
  The command to set these parameters is 'stty'. Watch:

  squinkyB ] stty erase ^h
  squinkyB ]

  There... that wasn't so bad, was it? Well, it's also pretty
  meaningless to you, unless you have the ascii table memorized and are
  pretty good at on-the-spot deduction.
  The tty erase parameters determines which key is to be used as a
  backspace. At times, this may already be set when you log in, or it
  may be set to a suitable alternate (such as delete). Most of the time
  the system will tell you when you log on if this is so. In this case,
  we've entered ^h in order to make the backspace key, appropriately
  enough, backspace.
  Another extremely important parameter is 'intr'. The 'intr' paramter
  tells the Unix system what you intend to use as a break character...
  you should have this set to ^c.

  Getting Around

  A good thing to remember about Unix is that it's alot like DOS. Files
  are laid out in directories just as in DOS... in fact, the only
  immediate difference in the directory structures is that Unix uses a
  forward slash ("/", moron!) instead of a backwards one.
  Also, the basic Unix directory navigation command is identical to DOS.
  In order to change directories, you use the command 'chdir', or 'cd'.
  A quick example:

  1 /usr1/astoria ] cd ..
  2 /usr ]

  Wala. That simple. Quick notes:

  ю cd / will take you to root.
  ю cd /*pathname* will take you to *pathname*
  ю cd home will take you to your home directory.

  You can make and delete your own directories with the mkdir/rmdir
  commands. Simply put, mkdir makes a subdirectory off of the current
  directory, and rmdir removes a subdirectory from the current
  subdirectory. Good to know if you plan to do a lot of file transfers.
  An important note about Unix directories, files, and concepts:
  Unix is a case-sensitive operating system. Thus, the files

  ю Spleen
  ю spleen
  ю SpLeEn

  are all different. This rule applies to directories and command line
  paramters, as well as most other Unix ideas.
  Another nice thing to know about Unix: Unix files are not subject to
  the normal DOS 8 character limit. Thus, you can have vast filenames,
  such as "this_file_ate_my_biscuit".

  Some other important commands

  First and foremost, you should know cp. cp is the basic Unix
  equivalent of the DOS COPY command. The command line for cp is
  identical to that of COPY.
  Next on the scale of cosmic import is cat. cat is the Unix equivalent
  of the DOS TYPE command, and once again, for simple file displaying,
  the command line is identical.
   Variations on the theme:
   pg: displayes a file page by page. Type "pg x filename", where x is a
       number of lines to display before pausing and filename is the
       file you wish to display.
   more: displays a file screen by screen.
   Stupid pet trick:
   You can use your cat to copy files, simply by using the directional
   operators. To copy a file from here to there using cat, simply type:

   % cat here
   this is the file here
   % cat there
   this is the file there
   % cat here > there
   % cat there
   this is the file here

   The operator ">" simply takes the output from the cat command and
   places is in the location specified after it.
  Another vital command to know is 'rm'. rm deletes a file from the
  system, in the same way DEL would on a DOS system. Not to much else to
  Critical in your navigation of a Unix system is the ls command. ls is
  DOS DIR on heroin. Simply type ls and you get a nice, neat list of
  files in the directory.
   DIR on controlled substances:
   There are a few command line parameters that you should know...
   foremost is l. ls -l gets you a list of files, and valuable
   information about each file, including permissions (more on that
   later), size, and linked files.
   Another useful command for long file lists is C. ls -C gets you a
   list of files in multiple columns, much the same as DIR /W would
   merit a double column report of all existing files. A quick reminder:
   ls -C is NOT the same as ls -c. Unix = case sensitive.
  Another good command to know, mv will move a file from directory to
  directory. For those of you without DOS 6.0 <gasp>, mv simply copies a
  file to another directory and deletes the original.
   quick tip for files on the lam:
   if you want to rename a file (to protect the innocent), you need to
   mv a file to a different file name. A quick demo:

   # ls
   # cat myfile
   this is my file
   # mv myfile my_other_file
   # ls
   # cat my_other_file
   this is my file

  Another vastly important command is 'man'. In fact, man is probably
  one of the most important commands extant for a beginning user... it
  calls up the system's help files. To use man, simply type in 'man
  command', where command is a Unix command you seek to gain
  enlightenment regarding. It's a great way to gain an understanding of
  Unix commandline parameters.
  If you are interested in seeing who's been on of late, or just want a
  few names to try to hack, type 'who'. You get a quick list of users
  that have accessed the system lately. If you <god forbid> need to know
  who you are at this point, type 'whoami'.
  If you want to change your identity on the system, type 'su name'
  where name is an account on the system. It'll ask you for the account
  password, then, *presto*... instant transmogrification.
   A Caveat for smart alec hackers:
   Unix typically logs usage of the su command. While su may seem like a
   great opportunity to try to hack out passwords manually without
   worrying about the system hanging up after 3 attempts, it's typically
   not a good idea to do this, as it may alert the administrators to
   your presence.
  *Numero Uno on the list of commands NEVER to use on a Unix system:
  The 'passwd' command changes your password on a Unix system. Seems
  innocous enough, eh? Uh-uh. If your account is active, and there's a
  very strong chance that it either is or will be, there is no better
  way to lose the account than to change the password, only to have the
  legitimate user alert the sysadmins when he/she can't gain access to
  his/her normal account (well, there are better ways... you could
  simply mail the sysadmin and tell him you are trying to hack his
  grandmother's life support machine through your account).
  I've seen this single, quick command turn a extremely lax system
  into an ironclad security compound in less than a day.
  *Numero Dos on that same list:
  The 'mail' command reads and sends mail. So what? Well, unless your
  account is stable (and it isn't unless you either paid for it or
  killed the original owner in such a way that his body cannot claw it's
  way out of it's grave to it's keyboard), the user is more likely than
  not going to know if you read his mail. In addition, if you send mail
  out of the system (type 'mail', and a username/address; type in your
  message and end it with a ^d on it's own line), the response from your
  message will likewise alert the user to your presence.

  System Spelunking

  The first place you want to check out in the wild uncharted directory
  tree of your friendly neighborhood Unix system is the "/etc"
  directory. What's in it? The single most intensely important file on
  the system (besides a world writable root owned SUID file... but don't
  worry about that)... the passwd file.
  What is in the passwd file?

  ю  a list of all accounts on the system
  ю  a list of the passwords for these accounts
  ю  a list of access levels for these accounts
  ю  a list of the home directories for these accounts
  ю  a list of information pertaining to these accounts.

  Why the hell the Unix designers decided this file should be world
  readable is beyond me. Be content to know that your standard everyday
  run-of-the-mill-lacking-in-certified-cosmic-power 'cat' command WILL
  display this file. As will pg and more. However, because most users
  don't have write permissions (more on that later) to the /etc
  directory, 'cat' is pretty much the only applicable command here.
  However, if you need to copy the file to your own directory (for
  whatever reason), just cat it there with the directional operator (>).
  The catch:
  Well, there are two catches here. First off, regardless of system
  security, if the passwords are in the file, they are encrypted. You
  can't decrypt them. Although you can get a list of accounts without
  passwords this way (just look for accounts with no entry in the
  password field), and a list of accounts that can't be logged onto
  remotely/at all (NO LOGIN), you can't get much else. Sucks, don't it?
  Notice I said 'if' the passwords are there.
  <ominous soundtrack please>
  Some horrible, paranoid, draconian system administrators mutilate
  their passwd files in such a way that (*gasp*) the passwords don't
  show up. All you get is one cold, icy X staring at you from the bowels
  of Unix Shell Siberia, mocking you as you pull your hair out in
  frustration (sorry, but this is a sore spot with me). The kidnapped
  passwords reside in the shadow file in the /etc directory, available
  with your standard everyday run-of-the-mill-but-distinct-in-the-fact-
  that-only-root-level-accounts-can-use-it-to-this-extent 'cat' command.
  Well, if the passwords are encrypted, what good are they?
  By themselves, nothing. A account with a Unix encrypted password will
  get you no further than an account with no listed password at all. You
  can't even deduce the amount of characters in the password if it's
  encrypted. So what's the use?
  The Unix method of encrypting files is available to the public. It is
  also, to most mortals, irreversable. Essentially, this means you can
  encrypt a string of characters, but not decrypt it. Even the unix
  system itself doesn't decrypt the password when you log on...
  When you log on, the Unix system takes whatever you enter at the
  password prompt, encrypts it, and matches it to the entry in the
  passwd file. Thus, the Unix system never decrypts the password... it
  only compares it to a different encrypted string.
  While this may not sound too particularly useful at first, it is.
  There are programs that have been written to do the same thing on a
  personal computer... you supply it a list of passwords and a list of
  words to attempt to use as passwords (called dictionaries), and it
  spends the night encrypting dictionaries and matching them to password
  entries. By running a dictionary through a passwd file, on a typical
  system, you can usually get 10-20 accounts. Good personal computer
  examples of this program idea include Killer Cracker (the industry
  standard, so to speak) and CrackerJack (faster than Killer Cracker).
   Quick tips for CrackerJunkies with leech access at an H/P BBS:
   A standard dictionary will not uncover passwords protected with an
   appended digit or non-alphanumeric character. In order to get around
   this, you need only grab a program that processes the dictionary file
   to add that digit to each entry in the dictionary... although this
   takes longer, and you'll need to do it multiple times, you can
   typically get 10 more accounts just by adding a 1 to every entry.
  Files and directories in Unix are characterized further by their
  permissions. Permissions are a standard system of who gets access to a
  specific function of that file or directory. Standard permissions
  include read, write, and execute. You can get a list of permissions by
  typing 'ls -l'. The first field in the listing contains the
  permissions, grouped as follows:

  owner  group   world
  rwx    rwx     rwx

  (Not drawn to scale... in fact, it doesn't look anything like that).
  Essentially, as long as the letter is there, you have access to that
  facet of the file. If the letter is not there, you'll see a dash...
  meaning you don't have access to that function. An example:


  In this case, the owner of the file can Read the file, Write to the
  file, and eXecute the file; members of his group (a bunch of linked
  accounts) can Read the file, CANNOT Write to the file, and can eXecute
  the file; and the rest of the user population CANNOT Read or Write to
  the file, but CAN eXecute the file.


  simply means that anyone can read, write, or execute the file.

  Another permission sometimes set to a file is the SUID bit. An SUID
  file contains a smallcase s in the user executable section of the
  permissions list...


  When you execute an SUID file, your user ID becomes that of the owner
  of the file. While this may not look to important at first, by now you
  should know that no really important super elite hacker concept does.
  Take a look at this:


  Synopsis? It's a world executable SUID file. In essence, anyone can
  execute the file, and in doing so, become the owner of the file for
  the duration of the time that file is operating. However, this doesn't
  get you much, because you typically can't do anything while the
  programis running. More likely than not, it's calculating how many
  pencils it needs to order for school tomorrow or some other such
  The real power of the SUID file comes into play in this situation:


  You won't see a lot of these, but when you do, look out. What you have
  here is a world writable SUID file... and a world writable program can
  be any program on the system you have read access to. Like, say,
  /bin/sh... the Unix shell...
  Quick command line example... 'diablo' is a root owned, world writable
  SUID file. I'm going to ignore the rest of the output of the ls

  #ls -l
  rwsrwxrwx... ...diablo
  #cat /bin/sh > diablo

  Oh, just so you know, the $ prompt denotes root access.
  Good deal, huh? In general, if you have right privs to an SUID file,
  copy it to your own directory and cat /bin/sh into it. You now have an
  instant gateway to the account of the owner of that file.
  If you want to find files that you can do this with, try this out:

  #find / -user root -perm -4000 -exec /bin/ls -al {} ";"

  This will give you a list of all root owned SUID files. If you want
  more info on the 'find' command, just 'man find'.

  Well, I'm overdo for an appointment on the IRC in #warez... so I'll
  cut off here. I hope I've been of assistance to you.

  A C T U A L  A R T I C L E  E N D S  H E R E . . .

  Please feel free to save an extra 1k of file space and invoke the DOS
  EDIT CUT command at the dotted line. Do not remove the rest of this
  article on penalty of law.

  S00P3R GR00P-3SQU3 GR33TZ / +HANX

  Greets go out to Nowhere Man, INC, THG, UNT, SaD, SoD, PTA, SOB
  Thanks to... ________________________
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  Current DWE Akshul M3mbre Boards:

  Nitro Burnin' Funny Cars    WHQ/DWEnet HOST     (312)582-1115  <XANAX>
  The Prodigal Sun            CHQ/MECCA           (312)238-3585  <ASRIEL>
  Dark Waters                 HQ/Infosite         (312)667-0222  <MONK>
  PyroTechnics II             Infosite            (708)991-9403  <PYRO>

  DWE M3/\/\B3R LiST

  President and Dictator for Life: Xanax
  Head Courier/Warez Cracker: Asriel
  Head Fisherman/Trout Expert: Changeling
  Head Person That Gets Asriel Free CDs: Monk
  Head Person That Gets DWE Members Free WaReZ: Pyro
  Head Person That Knows More Than Asriel (Honorary Title): LVX
  Head Person That Actually Wrote for DWE without Coercion: Cosmos
  Head Know-It-All Stoner that runs 386bsd: Goldstein

  Want to write for DWE? Neither do we. But if the spirit moves you,
  write up an article about anything we haven't discussed already, and
  post it somewhere in DWEnet or at any of the member boards, or call
  any of the members voice and dictate it to them, or submit it to them
  school newspaper of any of the members, or tack it on a bulletin board
  in the Third Coast Cafe in Century Mall, and chances are it'll be
  released as a s00per c00l DWE article.

 W H A T  F O L L O W S  M U S T  N O T  B E  D E L E T E D
  (c) 2003 Hackers-Network
  Asriel(tm) appears courtesy of Hasbro, Inc.

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