When run sqlplus the error appears: nls_lang.sh: 114: [[: not found

Solution is very simple: change the first line of this file from #! /bin/sha to #! /bin/bash and make fun :)

PL/SQL - Basics

Every PL/SQL program is made of PL/SQL code blocks. There are three types of PL/SQL code blocks:
1) anonymous - they are created in dynamic way and executed only once;
2) named:
- with etiquette - anonymous code blocks with an etiquette which allows to use variables declare inside of this code block;
- subprograms - function, procedures - stored in DB under some name and invoked many times;
- triggers - connected with DB events like invoking DML function (INSERT, UPDATE, DELETE) or DDL function (e.g CREATE, DROP)

How to install Oracle XE under Ubuntu

Installation of Oracle database under the Ubuntu linux system is very simple. You have to go through a few simple step which could make you feel a real DB administrator :). So...

1) Add adequate key to your apt repository

waldekd@waldekd-laptop:~$ wget http://oss.oracle.com/el4/RPM-GPG-KEY-oracle -O- | sudo apt-key add -
--2009-09-24 20:45:31-- http://oss.oracle.com/el4/RPM-GPG-KEY-oracle
Resolving oss.oracle.com... 141.146.12.120
Connecting to oss.oracle.com|141.146.12.120|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1744 (1.7K) [text/plain]
Saving to: `STDOUT'

100%[==================================================================================================================>] 1,744 --.-K/s in 0.01s

2009-09-24 20:45:31 (158 KB/s) - `-' saved [1744/1744]

OK

2) Update your repository

waldekd@waldekd-laptop:~$ sudo aptitude update
Hit http://pl.archive.ubuntu.com intrepid Release.gpg
Ign http://pl.archive.ubuntu.com intrepid/main Translation-en_US
Ign http://pl.archive.ubuntu.com intrepid/restricted Translation-en_US
Ign http://pl.archive.ubuntu.com intrepid/universe Translation-en_US
Ign http://pl.archive.ubuntu.com intrepid/multiverse Translation-en_US
Hit http://pl.archive.ubuntu.com intrepid-updates Release.gpg

3) Install Oracle DB

ldekd@waldekd-laptop:~$ sudo aptitude install oracle-xe
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Writing extended state information... Done
The following NEW packages will be installed:
libaio{a} oracle-xe
0 packages upgraded, 2 newly installed, 0 to remove and 2 not upgraded.
Need to get 221MB/221MB of archives. After unpacking 405MB will be used.
Do you want to continue? [Y/n/?]
Writing extended state information... Done
Get:1 http://oss.oracle.com unstable/non-free oracle-xe 10.2.0.1-1.1 [221MB]
Fetched 188MB in 26min20s (119kB/s)
Selecting previously deselected package libaio.
(Reading database ... 6132459 files and directories currently installed.)
Unpacking libaio (from .../libaio_0.3.104-1_i386.deb) ...
Selecting previously deselected package oracle-xe.
Unpacking oracle-xe (from .../oracle-xe_10.2.0.1-1.1_i386.deb) ...
Processing triggers for man-db ...
Setting up libaio (0.3.104-1) ...

Setting up oracle-xe (10.2.0.1-1.1) ...
update-rc.d: warning: /etc/init.d/oracle-xe missing LSB style header
Executing Post-install steps...
-e You must run '/etc/init.d/oracle-xe configure' as the root user to configure the database.


Processing triggers for libc6 ...
ldconfig deferred processing now taking place
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Writing extended state information... Done


4) Make some initial configuration

waldekd@waldekd-laptop:~$ sudo /etc/init.d/oracle-xe configure
[sudo] password for waldekd:

Oracle Database 10g Express Edition Configuration
-------------------------------------------------
This will configure on-boot properties of Oracle Database 10g Express
Edition. The following questions will determine whether the database should
be starting upon system boot, the ports it will use, and the passwords that
will be used for database accounts. Press to accept the defaults.
Ctrl-C will abort.

Specify the HTTP port that will be used for Oracle Application Express [8080]:

Specify a port that will be used for the database listener [1521]:

Specify a password to be used for database accounts. Note that the same
password will be used for SYS and SYSTEM. Oracle recommends the use of
different passwords for each database account. This can be done after
initial configuration:
Confirm the password:

Do you want Oracle Database 10g Express Edition to be started on boot (y/n) [y]:n

Starting Oracle Net Listener...Done
Configuring Database...Done
Starting Oracle Database 10g Express Edition Instance...Done
Installation Completed Successfully.
To access the Database Home Page go to "http://127.0.0.1:8080/apex"

5) Log in to an application to manage DB



6) Here you are :)



7) Sometimes after your system has been restarted there are some problems with user's permissions (you've got message "User [your_login] is not a member of group 'dba'". To solve it you have to simply add your user to dba group be using the following statement (change "waldekd" with your login):

waldekd@waldekd-laptop:~$ sudo usermod -a -G dba waldekd

Know Your UNIX System Administorator -- A Field Guide

KNOW YOUR UNIX SYSTEM ADMINISTRATOR -- A FIELD GUIDE

There are four major species of Unix sysad:

1) The TECHNICAL THUG. Usually a systems programmer who has been
forced into system administration; writes scripts in a polyglot of the
Bourne shell, sed, C, awk, perl, and APL.

2) The ADMINISTRATIVE FASCIST. Usually a retentive drone (or rarely,
a harridan ex-secretary) who has been forced into system
administration.

3) The MANIAC. Usually an aging cracker who discovered that neither
the Mossad nor Cuba are willing to pay a living wage for computer
espionage. Fell into system administration; occasionally approaches
major competitors with indesp schemes.

4) The IDIOT. Usually a cretin, morpohodite, or old COBOL programmer
selected to be the system administrator by a committee of cretins,
morphodites, and old COBOL programmers.

HOW TO IDENTIFY YOUR SYSTEM ADMINISTRATOR:


---------------- SITUATION: Low disk space. ----------------

TECHNICAL THUG: Writes a suite of scripts to monitor disk
usage, maintain a database of historic disk usage, predict future disk
usage via least squares regression analysis, identify users who are
more than a standard deviation over the mean, and send mail to the
offending parties. Places script in cron. Disk usage does not
change, since disk-hogs, by nature, either ignore script-generated
mail, or file it away in triplicate.

ADMINISTRATIVE FASCIST: Puts disk usage policy in motd. Uses
disk quotas. Allows no exceptions, thus crippling development work.
Locks accounts that go over quota.


MANIAC:
# cd /home
# rm -rf `du -s * | sort -rn | head -1 | awk '{print $2}'`;


IDIOT:
# cd /home
# cat `du -s * | sort -rn | head -1 | awk '{ printf "%s/*\n", $2}'` | compress


---------------- SITUATION: Excessive CPU usage. ----------------

TECHNICAL THUG: Writes a suite of scripts to monitor
processes, maintain a database of CPU usage, identify processes more
than a standard deviation over the norm, and renice offending
processes. Places script in cron. Ends up renicing the production
database into oblivion, bringing operations to a grinding halt, much
to the delight of the xtrek freaks.

ADMINISTRATIVE FASCIST: Puts CPU usage policy in motd. Uses
CPU quotas. Locks accounts that go over quota. Allows no exceptions,
thus crippling development work, much to the delight of the xtrek
freaks.


MANIAC:
# kill -9 `ps -augxww | sort -rn +8 -9 | head -1 | awk '{print $2}'`

IDIOT:
# compress -f `ps -augxww | sort -rn +8 -9 | head -1 | awk '{print $2}'`


---------------- SITUATION: New account creation. ----------------

TECHNICAL THUG: Writes perl script that creates home
directory, copies in incomprehensible default environment, and places
entries in /etc/passwd, /etc/shadow, and /etc/group. (By hand, NOT
with passmgmt.) Slaps on setuid bit; tells a nearby secretary to
handle new accounts. Usually, said secretary is still dithering over
the difference between 'enter' and 'return'; and so, no new accounts
are ever created.

ADMINISTRATIVE FASCIST: Puts new account policy in motd.
Since people without accounts cannot read the motd, nobody ever
fulfills the bureaucratic requirements; and so, no new accounts are
ever created.

MANIAC: "If you're too stupid to break in and create your own
account, I don't want you on the system. We've got too many goddamn
sh*t-for-brains a**holes on this box anyway."

IDIOT:

# cd /home; mkdir "Bob's home directory"
# echo "Bob Simon:gandalf:0:0::/dev/tty:compress -f" > /etc/passwd


---------------- SITUATION: Root disk fails. ----------------

TECHNICAL THUG: Repairs drive. Usually is able to repair
filesystem from boot monitor. Failing that, front-panel toggles
microkernel in and starts script on neighboring machine to load binary
boot code into broken machine, reformat and reinstall OS. Lets it run
over the weekend while he goes mountain climbing.


ADMINISTRATIVE FASCIST: Begins investigation to determine who
broke the drive. Refuses to fix system until culprit is identified
and charged for the equipment.


MANIAC, LARGE SYSTEM: Rips drive from system, uses
sledgehammer to smash same to flinders. Calls manufacturer, threatens
pets. Abuses field engineer while they put in a new drive and
reinstall the OS.
MANIAC, SMALL SYSTEM: Rips drive from system, uses ball-peen
hammer to smash same to flinders. Calls Requisitions, threatens pets.
Abuses bystanders while putting in new drive and reinstalling OS.

IDIOT: Doesn't notice anything wrong.


---------------- SITUATION: Poor network response. ----------------

TECHNICAL THUG: Writes scripts to monitor network, then
rewires entire machine room, improving response time by 2%. Shrugs
shoulders, says, "I've done all I can do," and goes mountain climbing.

ADMINISTRATIVE FASCIST: Puts network usage policy in motd.
Calls up Berkeley and AT&T, badgers whoever answers for network
quotas. Tries to get xtrek freaks fired.

MANIAC: Every two hours, pulls ethernet cable from wall and
waits for connections to time out.

IDIOT:
# compress -f /dev/en0


---------------- SITUATION: User questions. ----------------

TECHNICAL THUG: Hacks the code of emacs' doctor-mode to answer
new users questions. Doesn't bother to tell people how to start the
new "guru-mode", or for that matter, emacs.

ADMINISTRATIVE FASCIST: Puts user support policy in motd.
Maintains queue of questions. Answers them when he gets a chance,
often within two weeks of receipt of the proper form.

MANIAC: Screams at users until they go away. Sometimes
barters knowledge for powerful drink and/or sycophantic adulation.

IDIOT: Answers all questions to best of his knowledge until
the user realizes few UNIX systems support punched cards or JCL.


---------------- SITUATION: *Stupid* user questions. ----------------

TECHNICAL THUG: Answers question in hex, binary, postfix,
and/or French until user gives up and goes away.

ADMINISTRATIVE FASCIST: Locks user's account until user can
present documentation demonstrating their qualification to use the
machine.

MANIAC:
# cat >> ~luser/.cshrc
alias vi 'rm \!*;unalias vi;grep -v BoZo ~/.cshrc > ~/.z; mv -f ~/.z ~/.cshrc'
^D

IDIOT: Answers all questions to best of his knowledge.
Recruits user to system administration team.


---------------- SITUATION: Process accounting management. ----------------

TECHNICAL THUG: Ignores packaged accounting software; trusts
scripts to sniff out any problems & compute charges.

ADMINISTRATIVE FASCIST: Devotes 75% of disk space to
accounting records owned by root and chmod'ed 000.

MANIAC: Laughs fool head off at very mention of accounting.

IDIOT:
# lpr /etc/wtmp /usr/adm/paact


---------------- SITUATION: Religious war, BSD vs. System V. ----------------

TECHNICAL THUG: BSD. Crippled on System V boxes.

ADMINISTRATIVE FASCIST: System V. Horrified by the people who
use BSD. Places frequent calls to DEA.

MANIAC: Prefers BSD, but doesn't care as long as HIS processes
run quickly.

IDIOT:
# cd c:


---------------- SITUATION: Religious war, System V vs. AIX ----------------

TECHNICAL THUG: Weeps.

ADMINISTRATIVE FASCIST: AIX-- doesn't much care for the OS,
but loves the jackboots.

MANIAC: System V, but keeps AIX skills up, knowing full well
how much Big Financial Institutions love IBM...

IDIOT: AIX.


---------------- SITUATION: Balky printer daemons. ----------------

TECHNICAL THUG: Rewrites lpd in FORTH.

ADMINISTRATIVE FASCIST: Puts printer use policy in motd.
Calls customer support every time the printer freezes. Tries to get
user who submitted the most recent job fired.

MANIAC: Writes script that kills all the daemons, clears all
the print queues, and maybe restarts the daemons. Runs it once a hour
from cron.

IDIOT:
# kill -9 /dev/lp ; /dev/lp &


---------------- SITUATION: OS upgrade. ----------------

TECHNICAL THUG: Reads source code of new release, takes only
what he likes.


ADMINISTRATIVE FASCIST: Instigates lawsuit against the vendor
for having shipped a product with bugs in it in the first place.

MANIAC:

# uptime
1:33pm up 19 days, 22:49, 167 users, load average: 6.49, 6.45, 6.31
# wall
Well, it's upgrade time. Should take a few hours. And good luck on that
5:00 deadline, guys! We're all pulling for you!
^D

IDIOT:
# dd if=/dev/rmt8 of=/vmunix


---------------- SITUATION: Balky mail. ----------------

TECHNICAL THUG: Rewrites sendmail.cf from scratch. Rewrites
sendmail in SNOBOL. Hacks kernel to implement file locking. Hacks
kernel to implement "better" semaphores. Rewrites sendmail in
assembly. Hacks kernel to . . .

ADMINISTRATIVE FASCIST: Puts mail use policy in motd. Locks
accounts that go over mail use quota. Keeps quota low enough that
people go back to interoffice mail, thus solving problem.

MANIAC:
# kill -9 `ps -augxww | grep sendmail | awk '{print $2}'`
# rm -f /usr/spool/mail/*
# wall
Mail is down. Please use interoffice mail until we have it back up.
^D
# write max
I've got my boots and backpack. Ready to leave for Mount Tam?
^D

IDIOT:
# echo "HELP!" | mail tech_support.AT.vendor.com%kremvax%bitnet!BIFF!!!


---------------- SITUATION: Users want phone list application. ----------------

TECHNICAL THUG: Writes RDBMS in perl and Smalltalk. Users
give up and go back to post-it notes.

ADMINISTRATIVE FASCIST: Oracle. Users give up and go back to
post-it notes.

MANIAC: Tells the users to use flat files and grep, the way
God meant man to keep track of phone numbers. Users give up and go
back to post-it notes.

IDIOT:
% dd ibs=80 if=/dev/rdisk001s7 | grep "Fred"


@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@@@@@@@@@@@@@@@@@@@@@@@@@@@

OTHER GUIDELINES:


---------------- TYPICAL ROOT .cshrc FILE: ----------------


TECHNICAL THUG: Longer than eight kilobytes. Sources the
output of a perl script, rewrites itself.

ADMINISTRATIVE FASCIST: Typical lines include:
umask 777
alias cd 'cd \!*; rm -rf ching *hack mille omega rogue xtrek >& /dev/null &'

MANIAC: Typical lines include:
alias rm 'rm -rf \!*'
alias hose kill -9 '`ps -augxww | grep \!* | awk \'{print $2}\'`'
alias kill 'kill -9 \!* ; kill -9 \!* ; kill -9 \!*'
alias renice 'echo Renice\? You must mean kill -9.; kill -9 \!*'

IDIOT: Typical lines include:
alias dir ls
alias era rm
alias kitty cat
alias process_table ps
setenv DISPLAY vt100


---------------- HOBBIES, TECHNICAL: ----------------


TECHNICAL THUG: Writes entries for Obsfuscated C contest.
Optimizes INTERCAL scripts. Maintains ENIAC emulator. Virtual
reality .

ADMINISTRATIVE FASCIST: Bugs office. Audits card-key logs.
Modifies old TVs to listen in on cellular phone conversations.
Listens to police band.

MANIAC: Volunteers at Survival Research Labs. Bugs office.
Edits card-key logs. Modifies old TVs to listen in on cellular phone
conversations. Jams police band.

IDIOT: Ties shoes. Maintains COBOL decimal to roman numeral
converter. Rereads flowcharts from his salad days at Rand.


---------------- HOBBIES, NONTECHNICAL: ----------------


TECHNICAL THUG: Drinks "Smart Drinks." Attends raves. Hangs
out at poetry readings and Whole Earth Review events and tries to pick
up Birkenstock MOTAS.

ADMINISTRATIVE FASCIST: Reads _Readers Digest_ and _Mein
Kampf_. Sometimes turns up car radio and sings along to John Denver.
Golfs. Drinks gin martinis. Hangs out in yuppie bars and tries to
pick up dominatrixes.

MANIAC: Reads _Utne Reader_ and _Mein Kampf_. Faithfully
attends Dickies and Ramones concerts. Punches out people who say
"virtual reality." Drinks damn near anything, but favors Wild Turkey,
Black Bush, and grain alcohol. Hangs out in neighborhood bars and
tries to pick up MOTAS by drinking longshoremen under the table .

IDIOT: Reads _Time_ and _Newsweek_-- and *believes* them.
Drinks Jagermeister. Tries to pick up close blood relations-- often

COMPOUND SYSTEM ADMINISTRATORS:


TECHNICAL FASCIST: Hacks kernel & writes a horde of scripts to
prevent folk from ever using more than their fair share of system
resources. Resulting overhead and load brings system to its knees.

TECHNICAL MANIAC: Writes scripts that SEEM to be monitoring
the system, but are actually encrypting large lists of passwords.
Uses nearby nodes as beta test sites for worms.

TECHNICAL IDIOT: Writes superuser-run scripts that sooner or
later do an "rm -rf /".

FASCISTIC MANIAC: At first hint of cracker incursions, whether
real or imagined, shuts down system by triggering water-on-the-brain
detectors and Halon system.

FASCISTIC IDIOT:

# cp /dev/null /etc/passwd

MANIACAL IDIOT: Napalms the CPU.
-Stephan Zielinski

Song for C

Really good one :). Please give credit to mhtsa!australia!jason:basservax if the origins are requested.


"A Song for C" (To the tune of "The Girl from Ipanema")

slow and dumb and inefficient
the C compiler goes error seeking
and as it passes
each line it parses
it calls...

functions and more functions
trying to break up expressions
into the thirteen levels of precedence
the ops have

how can I try to improve it?
hoard up the tokens in buffers?
how can I stop the thing looping?
I can't do it all just for free
we need money for R&D

just leave out one semicolon
the parasitic errors roll on
and scroll the line
of the screen each time
as it screams...

old-fashioned initialization
use equals and try simplifying
near line eleven
plus or minus seven
or so

searching through linked lists of half-full
hash tables a la Berkeley
looking for every single
ident symbol
it finds

how can I possibly graft it
onto a stack architecture?
functional disunity!
and how can I tell PCC
its not coding for PDPs

slow and dumb and inefficient
the C compiler goes error seeking
and as it passes
each line it parses
it calls...

Recently I've come across a very funny page connected with the UNIX. It presents some possibilities how to the Unix could make you smiled in very simple way. Some examples was shown below.

Funny Unix csh/sh commands:

% cat "food in cans"
cat: can't open food in cans

% nice man woman
No manual entry for woman.

% make love
Make: Don't know how to make love. Stop.

% sleep with me
bad character

% got a light?
No match.

% man: why did you get a divorce?
man:: Too many arguments.

source

How to install Debian GNU/Linux system in quasi-remotely way

There's plenty of methods to install Linux system on a server. I'd like to present on of them which can be used when you have some restricted access to server (for example because you are ill and you are sitting in front of your computer inside of your home and you can only count on a person who is next to your server but he's, let's say, "computer idiot"). What can you do in this situation? Go through this simple step-by-step guide and the answer comes to your mind on its own.

Linux - Debian - package manager

To manage some packages you can use apt or aptitude application.
Apt application contains:
- apt-get - tool used for managing packages (do not use it anymore)
- apt-cache - tool used for managing cached packages
- apt-cdrom tools used for managing packages there are on the CD-ROM
- apt-key - for key management.

Nowadays trends tell linux users to avoid of using apt-get and use aptitude.

Linux - Shell - scripts

Each shell scripts should start as following:

#!/bin/bash

Variables
There are three kinds of variables:
- special variables;
- environment variables;
- application's variable.

Special varibles
Provider information about some process.

$# - list of arguments
$0 - name of shell scripts
$1, $2,... - script's parameters
$* - list of parameters pass to the script ("$1 $2 ...")
$@ - list of parameters ("$1" "$2" ...)
$$ - gets PID of the current process
$? - returns code of the last run process
$! - returns PID of invoked process

Application's variables
Application's variable are typeless although you can create it by declare function. Variables can be declared anywhere in a shell script as was shown below:

waldekd@waldekd-laptop:~$ v="VARIABLE"
waldekd@waldekd-laptop:~$ echo $v
VARIABLE


Arrays
We can use only one dimensional arrays by declaring it in one of shown ways:

waldekd@waldekd-laptop:~$ tab={el1,el2}
waldekd@waldekd-laptop:~$ tab[1]={el3}
waldekd@waldekd-laptop:~$ declare -a tab
waldekd@waldekd-laptop:~$ echo ${tab[1]}
{el3}
waldekd@waldekd-laptop:~$ echo ${tab[*]} --> returns "elem_1 elem_2 elem_3"...
waldekd@waldekd-laptop:~$ echo ${tab[@]} --> returns "elem_1" "elem_2" "elem_3"...


You can undeclare an array's element by using unset command:

waldekd@waldekd-laptop:~$ unset tab[1]
waldekd@waldekd-laptop:~$ unset tab[*]
waldekd@waldekd-laptop:~$ unset tab[@]


Array length is available with the following command:

waldekd@waldekd-laptop:~$ echo ${tab[*]}

We cal also use systems' commands:

#!/bin/bash
command=$(pwd)
echo "Current directory is $command"


Evaluating of arithmetical expressions

To evaluate of arithmetical expression you can use let command:

#!/bin/bash
a=10
b=5
let sum=a+b
echo $sum

or double brackets

#!/bin/bash
a=10
b=5
sum=$(( a+b ))
echo $sum

or square brackets

#!/bin/bash
a=10
b=5
sum=$[ a+b ]
echo $sum

Linux - Shell - environment variables basics

The shell is some kind of interface that provides user with the possibility of communication with the Linux system. The most knowable shell is bash.

Environment variables
Environment variables are variables which can make some impact on processes inside of Linux system. Every process in system has a set of associated variables. To get list of environment variables you can use prinenv command:

waldekd@waldekd-laptop:~$ printenv
ORBIT_SOCKETDIR=/tmp/orbit-waldekd
GPG_AGENT_INFO=/tmp/seahorse-8cKqMm/S.gpg-agent:5663:1
SHELL=/bin/bash
TERM=xterm
XDG_SESSION_COOKIE=a49832786c8078ae002e75914a91479b-1252662128.49103-538825691
GTK_RC_FILES=/etc/gtk/gtkrc:/home/waldekd/.gtkrc-1.2-gnome2


Setting environment variable
To set an environment variable use export command:

waldekd@waldekd-laptop:~$ export MYVAR=myvar
waldekd@waldekd-laptop:~$ printenv MYVAR
myvar

waldekd@waldekd-laptop:~$ export PATH=$PATH:/home/waldekd/Desktop/

Aliases

If some of Linux commands (or theirs combination) seem to be more difficult (or hard) to user you can create an alias to them.

waldekd@waldekd-laptop:~$ alias ll='ls -al'

To unset alias unalias command is available:

waldekd@waldekd-laptop:~$ unalias ll

To get list of defined aliases you can use alias command:

waldekd@waldekd-laptop:~$ alias
alias ll='ls -al'

Wedding ;)

Linux - users and group of users

There are three user types in Linux systems:
- root (as known as superuser) - has all access to all parts of Linux system
- system user - connected with some services inside of the system
- normal user.

Users' data is stored in /etc/passwd file. Each of rows in this file is connected with one user. Structure of each row is shown below.

login:password:UID:GID:name:homedir:shell

login - user's identifier
password - user's password (now it is usually stored in /etc/shadow file due to security improvement)
UID - User ID - root UID = 0, systems acount UID=100-999, user accounts UID>1000
GID - Group ID - number of main group of user
name - user's name (usually name and surname)
homedir - home dir of user
shell - default shell for user

For example this file can look like the following one:

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh

As it was mentioned before user passwords are stored in /etc/shadow file. Structure of rows from this file was shown below:

login:password:date1:num1:num2:num3:num4:date2:res

login - user's login
password - user's password (encoded)
User is able to insert some special characters in this place:
! or *- means that this account has been blocked
!! - user has not set any password yet
date - date of last password modification
num1 - number of days before the next password modification
num2 - number of days to change the password
num3 - number of days when the system informs user about password expiration
num4 - number of days after the account is blocked
date2 - date of block of account
res - reserved field

Example entry was shown below:

waldekd:$1$AZK6J/bg$BLkas/oh3BKHRas0b.3/f0:14479:0:99999:7:::

Every user in the Linux-based system belongs to one or more groups. Main group number connected with the user is included in the /etc/passwd file.
Groups' data is included in /etc/groups file.Each row from the file has structure as was shown below:

gr_name:pass:GID:users

gr_name - group name
pass - group password
GID - Group ID
users - users assigned to this group

Example file:
root:x:0:
daemon:x:1:
bin:x:2:
sys:x:3:
adm:x:4:waldekd
tty:x:5:
disk:x:6:
lp:x:7:
mail:x:8:
news:x:9:
uucp:x:10:

All passwords connected with group are stored in /etc/gshadow file. Its structure is similar to /etc/shadow file:

gr_name:pass:admins:users

gr_name - name of group
pass - group's password
admins - group's admins
users - users assigned to this group.

To get info about users and groups you can use command listed below:

id - prints info about UID, GID and other group user belongs to.
For example:

waldekd@waldekd-laptop:~$ id
uid=1000(waldekd) gid=1000(waldekd) groups=4(adm),20(dialout),24(cdrom),46(plugdev),108(lpadmin),123(admin),124(sambashare),1000(waldekd)

waldekd@waldekd-laptop:~$ id root
uid=0(root) gid=0(root) groups=0(root)

groups - lists group user belongs to.

waldekd@waldekd-laptop:~$ id root
uid=0(root) gid=0(root) groups=0(root)

finger - gets info about user.

waldekd@waldekd-laptop:~$ finger waldekd
Login: waldekd Name: Waldemar Dacko
Directory: /home/waldekd Shell: /bin/bash
On since Fri Sep 11 11:42 (CEST) on tty7 from :0
2 hours 34 minutes idle
On since Fri Sep 11 12:16 (CEST) on pts/0 from :0.0
No mail.
No Plan.

Adding user
To add some new user you can use on of these command:
useradd - creates some new user or modifies default settings of existing one.

waldekd@waldekd-laptop:~$ sudo useradd -d /home/magdalena -g users -s /bin/bash magdalena

If some of the settings are not provided by you the system defaults they according to the /etc/default/useradd file.
useradd -D modifies default settings.

adduser - adds user to the system

VIM

Well, I have heard a lot of various comments about this editor, but according to me (and not only) this is the most advanced text editor in the world. But there are some people who smiled looking at this post... For these people VI is so hard to learn. I understand that you prefer some scintilla-engine-based editor (like Scite, Notepad++ and many others) to VIM - this is your choice of course. But try VI at first and then comment it.

Below I have presented excellent sheet covers most of the VI commands (http://www.viemu.com/)

Linux - how to get some help

There are various of methods which helps you in getting some help.
man - the best known way of getting help (e.g. man who)
info - hypertext help system (e.g. info who)
apropos - looking for text strings inside of database of system commands (e.g. apropos who)

Linux - Hierarchical directory according to the FHS standard

For the Linux operating systems there are two main standards determine hierarchy of directories in main file system: FSSTND and FHS. The FHS is an improved version of FSSTND which is addressed not only for Linux systems but also for other Unix-like distributions.
According to the FHS all files there are in some hierarchical structure with one root "/" (it does not depend on whether these files are on one logic disc or many).

/bin/ - basic executable files available for all users
/boot/ - bootloader files
/dev/ - files connected with devices
/etc/ - configuration files
/home/ - home directories of users
/lib/ - libraries for programs from /bin and /sbin directories
/mnt/ - using for mounting file systems
/media/ - mount-points for removable devices
/opt/ - application compiled in statical way
/proc/ - informs about processes state
/root/ - home directory for root user
/sbin/ - application using for system management
/tmp/ - temporary files
/usr/ - second-level hierarchy sharing between users
/var/ - various types of files