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This table represents the order in which shell attributes are inherited

/etc/skel	default template for a new added users home directory
/etc/profile	sets environmental variables used by all users
/etc/profile.d	contains scripts specific to certain RPMS
/etc/bashrc	contains global aliass and system settings
~/.bash_profile	contains user environement settings and can be set to auto start programs at login
~/.bashrc	contains user aliases and functions

/etc/passwd File contains the configuration info for loacl users in the following format(world readable):

username : x: UID:GID:GECOS:homedir:shell

/etc/shadow File contains the username (which must match /etc/passwd) and the users MD5 encrypted password (only readable by root)

/etc/group file contains the configuration for local groups in the following format

groupname :x: GID : secondary users

/etc/gshadow file contains a list of groups on the server and their MD5 encrypted passwords.

useradd	used to add new users
usermod	used to modify the attributes of the user
groupadd	used to add new group to server
groupmod	used to change group attributes
passwd	used to create or change user passwords
chage	command used to create/edit password aging

Locating files with Special Permissions/attributes

find . / -perm +4000 |less

find root owned

find / -perm +2000  | less

get all GID/SUiD

find / -perm +1000 (sticky bit)

can be (used to find 777)

Setuid Suid Set UserID is used on Unix systems for tasks that require higher privileges. Has greatest impact on executable files.

chmod u+s <file>

setgid

chmod g+s  

or

chmod 2770 /some/directory

assigns group ownership to directories

example

Configure the users mike,chris and jamie

make these users part of the ru group

useradd -s /sbin/nologin ru
useradd chris -G ru -p '    ' 

(grub-md5-crypt can be used to generate system passwords)

configure the directory /home/ru so that each user can read,create, and modify files.

chmod 2770 /home/ru 

or

chmod u+s /home/ru

Cron

Five values are available for scheduling automated processes

minute  hour   day of month  month  day of week                       
0-58    0-23      1-31       1-12     0-7  (0 or 7 is Sun,3 ltr abrvs)

examples

1.) create a cronjob for the user root that checks the amount of availabe space on the system every friday at 12:34 pm

34     12     *     *     5     /bin/df -h >>root.out --to create a file
34     12     *     *     5     df -h 

will mail to crontab user (MAILTO=user to customize)

2.) Create a cronjob as a regular user that lists the contents of /tmp at 4:56 am on Monday,February 3

56 04 3 2 1 /bin/ls -alh /tmp >> /root/tmpspace.out

(this one will run on every monday and on the third. Day of week or day of month get applied when the condition is met) You will have to write the logic in the script or * for every monday or * from just the third

FILE COMMANDS

vi filename(S)	edit a file or files
vi -r filename	retrieve saved file after crash
ZZ, :wq, :x	save and exit
:q, :q!	quit;quit without saving
:w. :w fn	save file, save file as fn
:e filename	edit filename
:r filename	insert filename
:sh	drop to shell
:!cmd	run command cmd
:r !cmd	execute cmd and insert output
!movement cmd	pipe lines in movement through cmd

SEARCH AND REPLACE

/txt, ?txt	find txt forward or backward
?^txt	find next line that starts with txt
n, N	repeat last search forward, backward
R	replace text from current character

DELETING/INSERTING TEXT

dw w, dd, x	delete word, line, character
ndd, nx	delete n_ lines, _n characters
x, X	delete character forward,backward
D, D$	delete to end of line
d motion	delete from cursor to motion ($,0,etc.)
:>, :<	indent, outdent line
S	replace text with blank line
o, O	insert new line below, above current line
u	undo last change
.	repeat last change

CUT/COPY/PASTE

nyy, nY	copy n lines
yw, yy	copy word line
p, P	paste text after,before cursor
a, i	insert text after ,before cursor
A, I	insert text end, beginning of line

MOVING AROUND

nG	move to line n
h, l, k, j	left,right,up down one character
nb, nw	left or right, n words
CTRL-B, F	backward, forward one screen
CTRL-U, D	up,down one screen
$, G	go to end of line, end of file
O	go to beginning of line (zero)
), (	move to next, previous sentence
},{	move to next,previous paragraph
w, b	move forward, back one word
e	go to end of current or next word

WICKED COOL STUFF

~	change case
xp	transpose characters
j	combine current line with next
mp	create a mark called p
`p	return to p
d`x, y`x	del,copy text from mark to cursor
:>n	indent n lines

The command ‘fuser’ can help identify processes and their ownership

fuser -n tcp 443

This will also identify the user and process bound to the specified port number.