Ch03 Administration Utility

8/9/2019 Ch03 Administration Utility

1/19

SAIGONLAB 83 Nguyn Th Nh, P9, Q.Tn Bnh, Tp. HCM LPI 102

Chapter 03Chapter 03

Administration UtilitiesAdministration Utilities


2/19


System Information

Finding Files

Text Processing

Scheduling Processes


3/19


System Information

Identifying the Systemuname command show system information

hostname command identifies the current host

Eg:

$uname a

Linux SAIGONLAB 2.4.20-8 #1 Thu Mar 13 17:54:28EST 2003 i686 i686 i386 GNU/Linux

$hostname

SAIGONLAB

see man uname and man hostname know detailed

information.


4/19


System Information

System default files

Linux store some command defaults in file in/etc/default

Filename same as command nameEntries in the file take the form of environment

variable definitions

Detail of defaults defined in command manual page

File usually edited manually


5/19


System Information

Identifying and Communicating with Active Users

who command show who is currently logged on to thesame system

Information kept in /var/run/utmp

last command show a history of every login to the samesystem

Information kept in /var/log/wtmp

Whoami and id command identify the current user

w command like who, in addition to show what theydoing.


6/19


Talking to Users

write command to display a message on a users terminalUsers can disable messages using mesg n

Root can always write to a user

write all (wall) to display to all logged-in users

Userful for sending out broadcasts

Used by the system shutdown mechanism

talkcommand to set up a two-way dialogue


7/19


System Information

Login Prompts

Greeting message when login locally contain in/etc/issue

Greeting message when login remotely contain in

/etc/issue.netSome simple in /etc/issue and /etc/issue.net

%h :print node name

man issue more informaiton


8/19


Finding Files

The find command: locate files using specified searchcriteria:find directory search_criteria.. Action

Directory: where we will search from

search_criteria:

-name name find only files called name

-user name find only files owned by user name

-type letter find files of specified type:f, d, etc..

action:

-print print filename found-exec and {} \; executes given command

-ok and cmd {} \; executes command but prompts forconfirmation


9/19


Finding Files

The locate commandeg:$locate /etc/dhcpoutpout: /etc/dhcpd.conf

which command

eg:$which findoutput:/usr/bin/find

whereis commandeg:$whereis findoutput:/usr/bin/find /usr/share/man/man1/find.1.gz


10/19


File Command

Interpreting files: file command identify the contents ofany file on the linux system.

The file /usr/share/magic (/etc/magic) contain magicnumbers used to determine the contents of the files

recognized bye the file commandeg:

$file *

feed.dat: ASCII text

myproc.c C source coderunsys: command text


11/19


Text Processing

The grep familygrep command:

syntax: grep [option] pattern [files]options:

-v Output nonmatched lines

-c Output count of lines matched

-I ignore lower/upper case

-n mark each matched line with its relative line number

Other version of grep: fgrep, egrep(using man moreinformation).


12/19


Text Processing

Regular Expressions

Two forms: Basic(grep) and extended (egrep)

Can match literal strings

Beware of meta characters!

Special syntax:

bracket expressions: [^0123456789]

special ranges: [:digit:]

wildcards: * ? + {1,3}


13/19


Text Processing

Filter: many utilities read from stdin, process it in someway and output their result to stdout.

Some program: cat, head, tail, wcEg:

$

cat /etc/passwd$tail /etc/passwd$wc l /etc/passwd

Sed: allow automatic editing of text filessed s/lpi/lpi2/g lpi1.doc >lpi2.doc


14/19



at command: execute commands at a specified time.syntax: - Commands are read from stdin- Stdout and stderr are mailed to user

- Stdin is redirected from /dev/null- The job inherits current environmentCommands are run using the users shellUsef filename to have at read from a file rather than

stdineg: $at 8:00 tomorrow

echo Meeting at 9:30 today^D

Some options of at command: -l, -r and atq, and atrm

command.


15/19



The crontab command: run jobs at periodic intervals.

Syntax:

Space/tab separated columns

Specify comma-separated list or range of values

Field in cron table specify:

The users crontab files usually live under /var/cron/tabsor /var/spool/cron


16/19



crontab l [user]: list table cron table of user

Crontab e [user]: edit the cron table of user

If without user parameter, cron affect with current user.

Only super user can change crontab belong to other users.

An asterisk(*) in any of time fields mean all possible valuesfor this field.


17/19



Administering at and crontab: control and configurationfiles kept in /etc

at.allow users allowed to use at

at.deny users denied use of at(only used if no

at.allow)cron.allow users allowed to use cron

cron.deny users denied use of cron

crontab system cron table

Only root can use system cron table.

*.deny check if *.allow not exists.

*.deny empty and *.allow not exists:Permit all users access

to the utility.


18/19



Anacron: like cron, be designed for systems not running alltime.

Syntax:

Man anacron get more information


19/19


Summary

Demonstrate how to communicate with users

Identify system defaults

Demonstrate how to find files

Identify and use different text processing utilities such asgrep and sed

Explain process scheduling and process accounting

Date post:	30-May-2018
Category:	Documents
Upload:	m3onh0x84
View:	228 times
Download:	0 times

Ch03 Administration Utility

Documents