Tài liệu Tài liệu LPI-102 Junior Level Administration: Version 2.0
Lưu hành nội bộ
LPI-102
Junior Level Administration
Exam: 117-102
INDEX
Chapter 1 The Linux Documentation
Chapter 2 Managing Users
Chapter 3 Shells, Scripting, Programming and Compiling
Chapter 4 Boot, Initialization, Shutdown and Runlevels
Chapter 5 The Linux Kernel
Chapter 6 System Logging and Automation
Chapter 7 Maintain system
Chapter 8 Printing
Chapter 9 Networking Fundamentals
Chapter 10 Networking Services, Part 1
Chapter 11 Networking Services, Part 2
Chapter 12 Distributed File System
Chapter 13 Network Security
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
The Linux Documentation
Chapter 1
22 Last updated: 26 December 2003
Objectives
• Use and manage local system documentation
• Find Linux documentation on the Internet
• Notify users on system-related issues
LPI Topics
1.108.1 Use and manage local system documentation
This objective includes finding relevant man pages...
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Version 2.0
Lưu hành nội bộ
LPI-102
Junior Level Administration
Exam: 117-102
INDEX
Chapter 1 The Linux Documentation
Chapter 2 Managing Users
Chapter 3 Shells, Scripting, Programming and Compiling
Chapter 4 Boot, Initialization, Shutdown and Runlevels
Chapter 5 The Linux Kernel
Chapter 6 System Logging and Automation
Chapter 7 Maintain system
Chapter 8 Printing
Chapter 9 Networking Fundamentals
Chapter 10 Networking Services, Part 1
Chapter 11 Networking Services, Part 2
Chapter 12 Distributed File System
Chapter 13 Network Security
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
The Linux Documentation
Chapter 1
22 Last updated: 26 December 2003
Objectives
• Use and manage local system documentation
• Find Linux documentation on the Internet
• Notify users on system-related issues
LPI Topics
1.108.1 Use and manage local system documentation
This objective includes finding relevant man pages, searching man page
sections, finding commands and man pages related to them, and configuring
access to man sources and the man system. It also includes using system
documentation stored in /usr/share/doc/ and determining what
documentation to keep in /usr/share/doc/.
1.108.2 Find Linux documentation on the Internet
This objective includes using Linux documentation at sources such as the
Linux Documentation Project (LDP), vendor and third-party websites,
newsgroups, newsgroup archives, and mailing lists.
1.108.5 Notify users on system-related issues
This objective includes automating the communication process, e.g. through
logon messages.
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Different sources of help
• man, xman
• info, xinfo
• /usr/share/doc/howto
• /usr/share/doc/packages
Linux Documentation Project which is responsible for:
–ManPages
–FAQs
–HOWTOs
–Tutorials
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• You can get information about most commands.
• Man pages contains:
– Object name
– Synopsis and description
– List and definition of all options
– Environment and parameters
• Related commands are listed at the end of the man
page.
Man pages and the man command
Man page structure:
1. NAME
2. SYNOPSIS
3. DESCRIPTION
4. OPTIONS
5. EXIT CODE
6. CONFORMING TO
7. FILES
8. BUGS
9. SEE ALSO
10.AUTHOR
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Man pages and the man command
– Used to look up certain commands and their use.
– Man pages are divided in 9 sections
man [options] [section] command_name
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Kernel routines9
Administration commands8
Macro packages7
Games6
Configuration files and formats5
Devices (files in /dev)4
Library calls, e.g stdio3
System calls2
Information on executables1
man page sections
To view a particular section of the man pages, include the section number with the
man command and the term you are looking for:
man
Note:
When no type is given, the type search sequence until one is found is:
1,8,2,3,4,5,6,7,9
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• Spacebar Move forward one screen
• Return Move forward one line
• b Move back one screen
• f Move forward one screen
• q Quit the man command
• /string Find forward
• ?string Find back
• n Find the next occurrence of string
• h Help more
Scrolling in Man pages
Example:
$ man 8 mount
–displays the mount administration command
$ man 2 mount
–displays the mount system call
man -a command
–Display all the man page for the command . They are displayed one after the
other, each one being terminated with 'q'.
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Files, programs and variables
• /usr/bin/mandb
– Program to create or update the man page caches.
• MANPATH
– Contains the PATHs where mandb looks while indexing
pages.
• /usr/bin/manpath
– Program to display the paths searched for man pages.
• /etc/manpath.config
– mandb configuration file.
• man can be searched in multiple directories by setting the MANPATH variable.
MANPATH=/usr/man:/usr/X11R6/man:/usr/share/man
•If the MANPATH is not set then man will assume /usr/man
(Redhat: /usr/share/man)
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Files, programs and variables
• /usr/share/man/index.(bt|db|dir|pag)
– A traditional global 'whatis' index database cache.
• /var/cache/man/index.(bt|db|dir|pag)
– Alternate/FHS compliant global 'whatis' index database
cache.
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Locations of man pages
• /usr/man/*
– Old location of man pages
• /usr/share/man/*
– A global manual page hierarchy.
• /usr/local/man/*
– Extra man pages for user commands
• /usr/local/share/man/*
– Extra man pages for user commands
• /usr/X11R6/man/*
– X11 Applications man pages
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Locations of man pages
• /usr/X11R6/man/*
– X11 Applications man pages
• /opt/gnome/man/*
– Gnome Desktop applications man pages
• /opt/kde3/man/*
– KDE Desktop applications man pages
• /usr/openwin/man/*
– Openwindows Desktop applications man pages
• /var/cache/man/*
– catman pages files and index of manpages
Note:
–Most man pages in these directories are classified in subdirectories by their
respective type (sections) as in ..../man1/ ..../man2/
–The man pages are normally in compressed (.gz) GROFF source format.
They are decompressed automatically before the page is displayed.
–The cat pages are preformatted text man pages including the formatting
characters. They are normally saved in .../cat1 .../cat2 .... directories.
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PAGER variable
• The man pages use a display mode as less by default.
• Change display mode by change the PAGER
environment variable value.
• Example:
– less mode:
export PAGER=/usr/bin/less
– more mode
export PAGER=/usr/bin/more
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apropos command
– Searches short descriptions for the topic in the keywords
– Same result as:
man -k topic
• Example
$ apropos password
chage (1) - change user password expiry information
chpasswd (8) - update password file in batch
crypt (3) - password and data encryption
endpwent [getpwent] (3) - get password file entry
apropos topic
This command searches whatis database to get result.
So, you must create whatis database first.
# makewhatis
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whatis command
– Searches the man page keywords and presents the first short
description of the command.
– Same result as:
man -f command
• Example
$ whatis password
password: nothing appropriate
$ whatis passwd
passwd (1) - update a user's authentication tokens(s)
passwd (5) - password file
passwd [sslpasswd] (1ssl) - compute password hashes
whatis command
The exact command must be found otherwise nothing is displayed. It displays the
single line description found in the manpage. It first searches in the man page index
and then its own database if the man page index file is not found.
You must create whatis database first.
# makewhatis
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info Command
– Info pages are supposed to have more information than the
man pages.
– Some individuals write a short description of their programs
in the man pages and a longer one in the info pages.
• Example
$ info passwd
• Read passwd command info.
$ info 5 passwd
• View passwd file info.
info [section] [command]
Not all man pages are being maintained and are therefore out of date, so info yields
more current information.
Some topics treated in info are not discussed in man at all, info also uses hypertext
links, so it is a more powerful utility.
Navigation through info pages:
helph
last text displayedl
search * finds
directoryd
previous nodep
next node n
up node u
end of nodee
begin of nodeb
move backward, Page-Up-Key
move forward, Page-Down-Key
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Find Linux documentation on the Internet
•
– Linux Documentation Project
• The Linux Documentation Project web site. Contains Handbooks,
Books, HOWTOs, FAQs and lots more.
•
– The official Linux web site with more Documentation and
links to other Linux web sites.
•
– Google search engine for linux
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Find Linux documentation on the Internet
• Newsgroups
• Newsgroup Archives
• Mailing lists
Newsgroups
comp.os.linux.advocacy
General discussion about the advantages of using Linux vs. other OS.
comp.os.linux.announce
Commented Linux news
comp.os.linux.answers
Commented sending of Linux FAQ's. HOWTO's, and README's.
comp.os.linux.apps
General discussion about Linux Applications.
comp.os.linux.development.apps
Discussion about programming and porting applications for Linux.
comp.os.linux.development.system
Discussions about the Linux kernel, device drivers and loadable modules.
comp.os.linux.hardware
General discussion regarding Linux hardware compatibility.
comp.os.linux.misc
Different themes about Linux which are not found in other newsgroups.
comp.os.linux.networking
General discussions regarding networking and communications.
comp.os.linux.setup
General discussions regarding Linux installation and System Administration.
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comp.os.linux.x
Discussions about The X Window System under Linux.
alt.os.linux
General discussion regarding Linux.
Newsgroup Archives
Archives of all Newsgroups. Google has taken over this function.
Mailing lists
The following mailing lists are running off a central Majordomo server. To
subscribe to one of these mailing list, send an email to
majordomo@vger.kernel.org with the following as the mail text body:
subscribe ListName
ListName = One of the mailing lists below. The text in the subject area is
ignored.
linux-8086 linux-admin linux-alpha
linux-apps linux-arm linux-bbs
linux-c-programming linux-config linux-console
linux-diald linux-doc linux-fido
linux-fsf linux-ftp linux-gcc
linux-gcc-digest linux-hams linux-hppa
linux-ibcs2 linux-ipx linux-isdn
linux-japanese linux-kernel linux-kernel
linux-kernel-digest linux-kernel-patch linux-laptop
linux-linuxss linux-lugnuts linux-mca
linux-mips linux-msdos linux-msdos-digest
linux-msdow-devel linux-net linux-new-lists
linux-newbie linux-newbiew linux-nys
linux-oasg linux-oi linux-opengl
linux-pkg linux-ppp linux-pro
linux-qag linux-raid linux-scsi
linux-serial linux-seyon linux-smp
linux-sound linux-standards linux-svgalib
linux-tape linux-term linux-training@lists.iphil.net
linux-userfs linux-word linux-x11
linux-x25 sparclinux ultralinux
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Notify users on system-related issues
• /etc/issue
– pre-login message and identification file
• /etc/issue.net
– pre-login message and identification file, use for remote
user.
• /etc/motd
– message of the day.
– The contents of /etc/motd are displayed after a successful
login but just before it executes the login shell.
Login Sequence
When the system boots-up, right at the end of its default runlevel, init starts the
program mingetty for each virtual console defined in /etc/inittab.
Here is the sequence of events:
–The mingetty (getty) process displays the contents of the file /etc/issue.
–Then it displays the “HostName login:” prompt and waits for the user to enter
a username.
–When the username is entered and the user presses , mingetty
replaces itself with the program login and login gets the username from
mingetty and waits for the password from the user. login's configuration file
/etc/login.defs describes the behavior of login.
–If the file /etc/nologin exists, login will allow access only to root.
Other users will be shown the contents of this file and their logins will be
refused.
–If this authentication succeeds, the login process then starts a shell (usually
bash).
–bash reads its configuration scripts (/etc/profile etc.) and displays the content
of the file /etc/motd (message of the day), then displays its prompt.
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Overall sequence:
Escaped characters for /etc/issue
Waits for password
login--------------->
Shows /etc/motdShows /etc/issue
waits for user name and prompt
bash------------->mingetty
Kernel version (Buils Date) \v
The word User(s) and the Elapsed time since last login for this user.\U
Elapsed time since last login for this user\u
Present time.\t
Release number of the Kernel\r
Domain name\o
Hostname\n
System Architecture (eg. i386)\m
Name of the current TTY\l
Operating System Name (eg. 'Linux' )\s
Today's date\d
Baudrate of terminal connection (only for serial terminal connection)\b
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Summary
• Use and manage local system documentation
• Find Linux documentation on the Internet
• Notify users on system-related issues
Key files, terms, and utilities include:
MANPATH man
apropos
whatis
/etc/issue
/etc/issue.net
/etc/motd
22
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
Managing Users
Chapter 02
22 Last updated: 26 December 2003
Objectives
• add, remove, suspend and change user accounts
• add and remove groups
• change user/group info in passwd/group databases
• modify global and user profiles
• set environment variables
• maintain skel directories
LPI-102 Topics:
1.111.1 Manage users and group accounts and related system files
Description: Candidate should be able to add, remove, suspend and
change user accounts. Tasks include to add and remove groups, to
change user/group info in passwd/group databases. The objective also
includes creating special purpose and limited accounts.
1.111.2 Tune the user environment and system environment variables
Description: Candidate should be able to modify global and user
profiles. This includes setting environment variables, maintaining skel
directories for new user accounts and setting command search path
with the proper directory.
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Part 1
Manage Users
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User Account
• /etc/passwd
– information of all users: Login name, User ID, Group ID,
Descriptive name, Home directory, Login shell
• /etc/shadow
– stores parameters to control account access: user’s
password hash and password aging information
• /etc/group
– information about user’s groups
• /etc/gshadow
– stores group’s password hash,
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/etc/passwd
• Each line in this file correspond to a user
1. Login name
2. Password (or x if using a shadow file)
3. The UID
4. The GID
5. Text description for the user
6. The user’s home directory
7. The user’s shell
name:password:UID:GID:comment:home directory:shell
7654321
1. Username, up to 8 characters. Case-sensitive, usually all lowercase
2. the password field.
x = reference to /etc/shadow,
empty = no password,
* or ! = no login possible
3. Numeric user id. This is assigned by the ``adduser'' script. Unix uses this field,
plus the following group field, to identify which files belong to the user.
4. Numeric group id. Red Hat uses group id's in a fairly unique manner for enhanced
file security. Usually the group id will match the user id.
5. Full name of user. I'm not sure what the maximum length for this field is, but try
to keep it reasonable (under 30 characters).
6. User's home directory. Usually /home/username (eg. /home/smithj). All
user's personal files, web pages, mail forwarding, etc. will be stored here.
7. User's "shell account". Often set to “/bin/bash” to provide access to the bash
shell (my personal favorite shell).
# cat /etc/passwd
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/etc/passwd
# cat /etc/passwd | grep root
root:$1$K05gMbOv$b7ryoKGTd2hDrW2sT.h:0:0:Super User:/root:/bin/bash
# cat /etc/passwd | grep root
root:x:0:0:Super User:/root:/bin/bash
# cat /etc/shadow | grep root
root:$1$K05gMbOv$b7ryoKGTd2hDrW2sT.h:::::::
Traditional Unix systems keep user account information, including one-way encrypted
passwords, in a text file called “/etc/passwd”. As this file is used by many tools
(such as “ls”) to display file ownerships, etc. by matching user id #'s with the user's
names, the file needs to be world-readable. Consequentally, this can be somewhat of a
security risk.
Another method of storing account information, one that I always use, is with the
shadow password format. As with the traditional method, this method stores account
information in the /etc/passwd file in a compatible format. However, the
password is stored as a single "x" character (ie. not actually stored in this file). A
second file, called “/etc/shadow”, contains encrypted password as well as other
information such as account or password expiration values, etc. The /etc/shadow file
is readable only by the root account and is therefore less of a security risk.
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/etc/shadow
A reserved field9
Absolute date, beyond which the account will be disabled8
Number of inactivity days allowed for this user7
Number of days before expiration that user will be warned6
Maximum number of days password is valid5
Minimum number of days between password changes4
Number of days since the last password change, from 1/1/703
Encrypted password. 2
User login name, mapped to /etc/passwd1
name:password:lastchange:min:max:warn:inactive:expire:flag
87 9654321
CommentsDescription#
Reserved for future use9
empty = will never be disabledDays since Jan 1,1970 when account will be
disabled
8
empty= never inactiveDays before account becomes inactive7
empty=no warningDays warning before expiration6
Normal is 10000 daysDays before change required5
0=always allowed to changeDays until change allowed4
never emptyDays since Jan 1, 1970 when password was last
changed
3
empty = no password
* = no login possible
Encrypted password2
User login name1
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Create / Delete shadow
– Convert passwd --> shadow
– Convert shadow --> passwd
/usr/sbin/pwconv
/usr/sbin/pwunconv
• pwconv command will remove passwords from /etc/passwd and store in the
/etc/shadow
• Password field in /etc/passwd is replaced by an ‘x’
• Process can be reversed with the pwunconv command
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– Create new user
– Save user information to /etc/passwd and /etc/shadow
• Options
Make new user
Secondary groups-G GID
Specify login shell-s shell
Skeleton directory-k skel_dir
Make home directory-m
Specify home directory-d directory
Description of user-c comment
Specify primary group-g GID
Specify new user ID-u UID
useradd [options] new_user
•Several users pre-configured and assigned with UID less than 100:
root, bin, daemon, sys, adm, lp,
•Administration tools allocate UIDs automatically, greater than 100 in general
Skeleton directory ( default /etc/skel )-k skel_dir
List system Defaults-D
Specify login shell ( default /bin/bash )-s shell
Make home directory if it does not exist.-m
Define home directory ( default /home/username )-d directory
Description of user ( default: blank )-c comment
A list of supplementary groups which the user is also a member of.
Each group is separated from the next by a comma, with no
intervening white space.
-G GID
Specify default (primary) group ( default other group )-g GID
Specify new user ID (default: next available number)-u UID
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Make new user
• Example
# groupadd lpiusers
# useradd -g lpiusers -d /home/lpi102 -m -c "LPI's Member" lpi102
# grep lpi102 /etc/passwd
lpi102:x:504:556:LPI's Member:/home/lpi102:/bin/bash
#
Example: List system default
# useradd -D
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
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File: login.defs
– the mail spool directory
• MAIL_DIR
– password aging controls
• PASS_MAX_DAYS, PASS_MIN_DAYS, PASS_MAX_LEN,
PASS_WARN_AGE
– max/min values for automatic UID selection in useradd
• UID_MIN, UID_MAX
– max/min values for automatic GID selection in groupadd
• GID_MIN, GID_MAX
– automatically create a home directory with useradd
• CREATE_HOME
/etc/login.defs
# cat /etc/login.defs
MAIL_DIR /var/spool/mail
PASS_MAX_DAYS 99999
PASS_MIN_DAYS 0
PASS_MIN_LEN 5
PASS_WARN_AGE 7
UID_MIN 500
UID_MAX 60000
GID_MIN 500
GID_MAX 60000
CREATE_HOME yes
#
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Directory: skel
– Contains default files that will be copied to the home
directory of newly created users:
• .bashrc
• .bash_profiles
• ...
/etc/skel/*
# ls -la /etc/skel/
total 20
drwxr-xr-x 2 root root 4096 Sep 6 18:41 .
drwxr-xr-x 33 root root 4096 Nov 3 10:47 ..
-rw-r--r-- 1 root root 24 Feb 11 2003 .bash_logout
-rw-r--r-- 1 root root 191 Feb 11 2003 .bash_profile
-rw-r--r-- 1 root root 124 Feb 11 2003 .bashrc
#
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Change Password
– l Superuser command which locks account passwd
• Example
# passwd blobby
New password:
Re-enter new password:
Password changed
passwd [-l] username
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Modify user
– Changing User Attributes
• Options
– d the users directory
– g the users initial GID
– l the user's login name
– u the user's UID
– s the default shell.
• Notice these options are the same as for useradd
usermod [options] username
If you edit files manually, you risk corrupting file, resulting with users not being able
to log in at all. Instead, use usermod utility
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Changing Group Membership
• Example
# usermod –g users –c “Henry Blake” henry
# usermod –u 321 –s /bin/ksh majorh
# usermod –e 2004-12-20 majorh
Each user belongs to a primary group:
usermod –g
User can also belongs to secondary groups:
usermod –G
# grep figo /etc/passwd
figo:x:416:400::/home/figo:/bin/bash
# groupadd –g 600 realmadrid
# usermod –g realmarid figo
# grep realmadrid /etc/group
realmadrid:x:600:figo
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Removing Users
userdel [option] username
– Remove user from system
• Options
– r This option will remove home directory
When a user leaves, there are two main concerns:
–Protect the system from unauthorized access via his/her account
–Protect and manage his/her files, directories left on the system.
The userdel command takes care of removing a user account. userdel can
remove user’s home directory but does not user’s mail, crontab table, atd queues,
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Managing Groups
• Group commands and files
– /etc/group
– /etc/gshadow
– groupadd
– groupmod
– groupdel
– gpasswd
– id
– groups
Groups not only allow for a second level of access control but also allow the members
in group to share files in secured environment.
Every new user is assigned to an initial (or primary) group. Two conventions exist.
–Traditionally this primary group is the same for all users and is called users
with a group id (GID) of 100. Many Linux distributions adhere to this
convention such as Suse and Debian.
–The User Private Group scheme (UPG) was introduced by RedHat and
changes this convention without changing the way in which UNIX groups
work. With UPG each new user belongs to their own primary group. The
group has the same name as the login-name (default), and the GID is in the
500 to 60000 range (same as UIDs).
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/etc/group
– Contains a list of groups, each on a separate line.
1. Group name
2. The group password (or x if gshadow file exists)
3. The GID
4. A comma separated list of members
• Example
daemon:x:2:root,bin,daemon
name:password:GID:MEMBERs
4321
The /etc/group is world-readable. Each line is a four field, colon delimited list
including the following information:
Group name
–The name of the group. Used by various utility programs to identify the
group.
Group password
–If set, this allows users who are not part of the group to join the group by
using the newgrp command and typing the password stored here. If a lower
case x is in this field, then shadow group passwords are being used.
Group ID (GID)
–The numerical equivalent of the group name. It is used by the system and
applications when determining access privileges.
Member list
–A comma delimited list of users in the group.
# cat /etc/group
root:x:0:root
bin:x:1:root,bin,daemon
daemon:x:2:root,bin,daemon
....
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/etc/gshadow
– Contains an encrypted password for each group.
1. Group name
2. The group password
3. Group Administrators
4. Group Members
• Example
general:!!:shelley:juan,bob
name:password:GroupAdmins:MEMBERs
4321
The /etc/gshadow file is readable only by the root user, and contains an encrypted
password for each group, as well as group membership and administrator information.
Just as in the /etc/group file, each group's information is on a separate line. Each of
these lines is a four field, colon delimited list including the following information:
Group name
–The name of the group. Used by various utility programs to identify the
group.
Encrypted password
–The encrypted password for the group. If set, non-members of the group can
join the group by typing the password for that group using the newgrp
command. If the value is of this field ! then no user is allowed to access the
group using the newgrp command. A value of !! is treated the same as a value
of ! only it indicates that a password has never been set before. If the value is
null, only group members can log into the group.
Group administrators
–Group members listed here (in a comma delimited list) can add or remove
group members using the gpasswd command.
Group members
–Group members listed here (in a comma delimited list) are regular, non-
administrative members of the group.
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Group commands
– Add group to the system.
• Option
– g gid The numerical value of the group's ID.
• Example
# groupadd -g 501 lpiusers
# cat /etc/group | grep –i lpiusers
lpiusers:x:501:
groupadd [option] groupname
-g gid
The numerical value of the group's ID. This value must be unique, unless the -
o option is used. The value must be non-negative. The default is to use the
smallest ID value greater than 500 and greater than every other group. Values
between 0 and 499 are typically reserved for system accounts.
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Group commands
– modify the parameters of group
• Option
– n NewName change the name of group to NewName
– g gid The numerical value of the group's ID.
• Example
# groupmod –g 505 lpiusers
# cat /etc/group | grep –i lpiusers
lpiusers:x:505:
groupmod [option] groupname
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Group commands
– Delete group from the system.
• Example
# groupdel lpiusers
# cat /etc/group | grep –i lpiusers
#
groupdel groupname
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Group commands
– Change Group’s password
• Example
# groupadd lpiusers
# gpasswd lpiusers
Changing the password for group lpiusers
New Password:
Re-enter new password:
#
gpasswd groupname
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Create/Delete gshadow
– creates the /etc/gshadow file
– deletes the gshadow file
/usr/sbin/grpconv
/usr/sbin/grpunconv
• grpconv command will remove passwords from /etc/group and store in the
/etc/gshadow
• Password field in /etc/group is replaced by an ‘x’
• Process can be reversed with the grpunconv command
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Group commands
– List group ID
– List groups
• Example
# id
uid=0(root) gid=0(root) groups=0(root), 1(bin),
2(daemon), 3(sys), 4(adm), 10(wheel), 600(sales)
# groups
root bin daemon sys adm wheel sales
id
groups
A user can belong to any number of groups. However at any one time (when creating
a file for example) only one group is the effective group.
The list of all groups a user belongs to is obtained with either the groups or id
commands.
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– changes the number of days between password changes and the date of
the last password change.
• Options
Account Security
Warning days-W
Expiration (YYYY-MM-DD or MM/DD/YY)-E
Inactive lock-I
Day last changed-d
Maximum days-M
Minimum days-m
chage [options]
# chage -E 4/3/2002 blobby
# chage -l blobby
Minimum: 0
Maximum: 99999
Warning: 7
Inactive: -1
Last Change: Feb 06, 2002
Password Expires: Never
Password Inactive:
NeverAccount
Expires: Apr 03, 2002
# chage -l blobby
Minimum: 0
Maximum: 99999
Warning: 7
Inactive: -1
Last Change: Feb 06, 2002
Password Expires: Never
Password Inactive: Never
Account Expires: Never
27
Solution for chage command:
1. Lock the account password until you are ready to remove it
# chage –E 1999-01-01 figo
2. Save all file owned by the user somewhere outside the home directory
# find / -user henry –print | cpio ov | gzip >/hold/henry
# find / -user henry –type f –exec rm –f {} \;
# find / -user henry –type d –depth –exec rmdir {}\;
3. Change access permission on saved files to root only
# chown root /home/figo ; chmod 700 /home/figo
4. Consider crontab and at jobs setup by the user
5. Setup mail forwarding to send mail to a manager
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User and Group guidelines
• Use passwd command to change the password
# passwd
current password :
new password:
retype new password:
Choosing password:
• Not use proper words or names
• Use letters and digits
• Include symbols: !, @, #, $, %,
• Do not allow guest account to login to your system.
When creating a password, it is a good idea to follow these guidelines:
Do Not Do the Following:
1. Do Not Use Only Words or Numbers — You should never use only
numbers or words in a password.
– Some examples include the following:
8675309
juan
hackme
2. Do Not Use Recognizable Words — Words such as proper names,
dictionary words, or even terms from television shows or novels should be
avoided, even if they are bookended with numbers.
john1
DS-9
mentat123
3. Do Not Use Words in Foreign Languages — Password cracking programs
often check against word lists that encompass dictionaries of many
languages. Relying on foreign languages for secure passwords is of little
use.
29
– Some examples include the following:
cheguevara
bienvenido1
1dumbKopf
4. Do Not Use Hacker Terminology — If you think you are elite because you
use hacker terminology — also called l337 (LEET) speak — in your
password, think again. Many word lists include LEET speak.
– Some examples include the following:
H4X0R
1337
5. Do Not Use Personal Information — Steer clear of personal information. If
the attacker knows who you are, they will have an easier time figuring out
your password if it includes information such as:
• Your name
• The names of pets
• The names of family members
• Any birth dates
• Your phone number or zip code
6. Do Not Invert Recognizable Words — Good password checkers always
reverse common words, so inverting a bad password does not make it any
more secure.
– Some examples include the following:
R0X4H
nauj
9-DS
7. Do Not Write Down Your Password — Never store your password on
paper. It is much safer to memorize it.
8. Do Not Use the Same Password For All Machines — It is important that
you make separate passwords for each machine. This way if one system is
compromised, all of your machines will not be immediately at risk.
30
Do the Following:
1. Make the Password At Least Eight Characters Long — The longer the
password is, the better. If you are using MD5 passwords, it should be 15
characters long or longer. With DES passwords, use the maximum length -
eight characters.
2. Mix Upper and Lower Case Letters — Red Hat Linux is case sensitive, so
mix cases to enhance the strength of the password.
3. Mix Letters and Numbers — Adding numbers to passwords, especially
when added to the middle (not just at the beginning or the end), can
enhance password strength.
4. Include Non-Alphanumeric Characters — Special characters such as &, $,
and > can greatly improve the strength of a password.
5. Pick a Password You Can Remember — The best password in the world
does you little good if you cannot remember it. So use acronyms or other
mnemonic devices to aid in memorizing passwords.
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Part 2
User Environment
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/etc/profile
$ cat /etc/profile
if [ `id -u` = 0 ]; then
pathmunge /sbin
pathmunge /usr/sbin
pathmunge /usr/local/sbin
fi
# No core files by default
ulimit -S -c 0 > /dev/null 2>&1
USER="`id -un`"
LOGNAME=$USER
MAIL="/var/spool/mail/$USER"
HOSTNAME=`/bin/hostname`
HISTSIZE=1000
export PATH USER LOGNAME MAIL HOSTNAME HISTSIZE INPUTRC
/etc/profile
Files and commands to be executed at login or startup time by the Bourne or C
shells. These allow the system administrator to set global defaults for all users.
/etc/profile.d
Shells scripts to be executed upon login to the Bourne or C shells. These
scripts are normally called from the /etc/profile file.
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Environment Files
SYSTEM WIDE:
/etc/profile /etc/bashrc
USER 1
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
USER 1
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
USER 2
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
USER 2
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
USER 3
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
USER 3
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
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Environment Files
login /etc/profile
~/.bash_profile
~/.bash_profile ~/.bash_login
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
/etc/bashrc
yes yes
no no
bash start
logout
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Environment Variables commands
• set
– shows all variables (local and exported)
• env
– shows only exported variables
• unset
– used to remove variables
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• export
– shows exported variables
• export
– make as exported (global) variables
Environment Variables commands
VAR=value
VAR=??
parent
child
LOCAL
export VAR=value
VAR=value
parent
child
GLOBAL
-When you defile new variable as local variable (without export), any child processes
can not use it.
-Global variable (with export) allow child processes use it.
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Summary
• Manage users and group accounts and related system
files
• Tune the user environment and system environment
variables
Key files, terms, and utilities include:
chage
gpasswd
groupadd
groupdel
groupmod
grpconv
grpunconv
passwd
pwconv
pwunconv
useradd
userdel
usermod
env
export
set
unset
/etc/passwd
/etc/shadow
/etc/group
/etc/gshadow
/etc/profile
/etc/skel
CommandsFiles
38
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
Shells, Scripting and Programing
Chapter 03
22 Last updated: 26 December 2003
Objectives
• Identify Linux shell environments
• Write and configure BASH script using variables, flow
controls interactive input, functions, arithmetic and
arrays
LPI Topics
1.109.1 Customize and use the shell environment
Candidate should be able to customize shell environments to meet users'
needs. This objective includes setting environment variables (e.g. PATH) at
login or when spawning a new shell. It also includes writing bash functions for
frequently used sequences of commands.
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Introduction
• Shell is a interface between OS and user. It provides :
– A facility for launching and managing commands and
programs
– An operating environment
– A programming language
– ...
# cat test.sh
#!/bin/bash
cd /var/log
grep “Error” *.log
Shell script :
–a text file that contains a list of commands, variables, comments, flow control
structures, loops, functions,
–All comments begin with # except #!
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Shell Configuration Files
• Type of configuration files :
– Global (system-wide) : apply to all users.
– Local : apply to each user.
• bash configuration files :
– Global: /etc/profile
– Local:
• ~/.bash_profile
• ~/.bash_login
• ~/.profile
Type of shell :
–Bourne shell (sh)
–Bourne Again shell (bash)
–Korn shell (ksh)
–C shell (csh,tcsh)
–...
A new shell is started when a programs is started;
and it will have separate environments: parameters, variables, functions, aliases ...
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Shell Environment
• Environment: variables, functions, aliases,...
• Type of variables: local (shell variable), global
(environment variable)
• Commands
– set : define a new variable
– unset : undefine a variable
– export: make a local variable becomes a global variable
– set : list all local variables
– env : list all global variables
Default environment variables:
–PS1, PS2
–HOME, PATH, PWD
–LOGNAME
–SHELL
–PAGER, LPDEST, DISPLAY
–...
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Redirecting Input and Output
• Redirect input : use (<) or (<0)
• Redirect output, overwrite : use (>) or (1>)
( Use set –o noclobber : prevent file overwriting )
# mailx admin@saigonctt.com < content
# ls –l > list_file
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Redirecting Input and Output
• Redirect output, append : use (>>)
• Redirect error : use (2>)
# ls –l >> list_file
# ls –l > list_file 2>&1
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Pipe and Back ticks ` `
• Pipe ( | ) : command1 | command2
– Output of command1 becomes input of command2
• Back ticks (` `) or “$()”
# ls –l |grep samba
# which passwd
/usr/bin/passwd
# ls –l /usr/bin/passwd
# ls –l `which passwd`
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Shell Scripts Variables
• Naming :
– not begin with a digit, usually in upper case letters
• Assigning : not SPACES around “=“
VAR=value : assign value string to VAR
VAR=`cmd` : the same VAR=$(cmd) , assign output of cmd to VAR
# VAR1=`ls /var/log | wc –l`
# echo $VAR1
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Shell Scripts Variables
• Variable declaration:
• Options:
-i integer
-r read-only
-x export: variable retains value outside script
declare –i vcount=1
declare –r vwellcome=‘Hello World’
$ declare =
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Shell Scripts Variables
• Single quotation ' '
– Ignore all special characters
• Double quotation " "
– Ignore all special characters, except $ ' ' \
# VAR=“Hello World”
# echo “$VAR”
Hello World
# echo ‘$VAR’
$VAR
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Variable Notation
• Use ${VAR}
# VAR1=“This is a String” ; echo $VAR1
This is a String
# VAR2=“$VAR1xyz” ; echo $VAR2
Nothing #default
# VAR3=“${VAR1}xyz” ; echo $VAR3
This is a Stringxyz
# VAR4=‘${VAR1}xyz’ ; echo $VAR4
${VAR1}xyz
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Passing Information to Script
• On the command line, information can be passed to
script through pre-set positional parameters
– $0 The name of the script
– $1-$9 Parameters are being passed to script
– $* List all variables entered at command line
– $# Number of parameters
– $! PID of the most recent backgroud command
– $$ PID of the current SHELL
The shift command will shift the positional parameters one or more position from left
to right
$1 --> $2
$2 --> $3
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Return codes/Exit status
• The variable $? contains the return code of the
previous executed command or application.
– 0 Success
– ≠0 Failure
• The exit n command will cause the script to quit
and assign the value of n to $? variable
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Flow control
• Loop : do something more than one time
• Loop commands : for, while, until
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The for Loop
• Syntax :
for in
do
# list of commands to do
done
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The for Loop Example
• This script will rename all file .txt in current
directory to .html
#!/bin/bash
for files in $(ls *.txt)
do
newname=“$(basename $file .txt).html”
mv $file $newname
done
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The while and until Loop
• Syntax :
while
do
# list of commands to do
done
until
do
# list of commands to do
done
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The while loop Example
• Code:
• Output :
0
1
2
3
count=0
while [ $count –lt 4 ]
do
echo $count
count=$((count+1))
done
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The until Loop Example
• Code:
• Output :
0
1
2
3
count=0
until [ $count –ge 4 ]
do
echo $count
count=$((count+1))
done
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Tests and Conditions
• Test command
test FILE
• Option:
-d FILE : FILE exists and is directory
-f FILE : FILE exists and is file
-e FILE : FILE exists
-x FILE : FILE is executable
-r FILE : FILE is readable
-w FILE : FILE is writable
-O FILE : FILE is owned by your UID
Example: bash exists and executable ?
test –x /bin/bash
Or
[ -f /bin/bash ]
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Condition Operators
Ex:
-lt : <
-gt : >
-le : <=
-ge : >=
-eq : =
-ne : !=
$VAR1 -eq $VAR2 : VAR1 = VAR2
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Tests and Conditions
• Test : use “[ ]” around expression
• If-then-else structure:
if [ ] # include SPACEs
then
#commands to do if the exp1 is true
elif [ ]
then
#commands to do if the exp2 is true
else
#commands to do if the exp1 and exp2 is NOT true
fi
Example: scriptx.sh
#!/bin/bash
declare name
declare cmd
echo –n “Enter name: “ ; read name
cmd=$1
if [ “$1” = “Hello” ]
then
echo “Hello $name”
elif [ “$cmd” = “Good-bye” ]
then
echo “Bye $name”
else
echo “Did not understand”
done
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case Structure
case expression in
pattern1 )
action
;;
pattern2 )
action
;;
* )
default action
esac
Where:
text) Condition Text
D|d) Multiple values for conditions: | = or
*) Default case
;; End of condition break
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case Test Example
#!/bin/bash
echo; echo "Hit a key, then hit return."
read Keypress
case "$Keypress" in
[a-z] ) echo "Lowercase letter“
;;
[A-Z] ) echo "Uppercase letter“
;;
[0-9] ) echo "Digit“
;;
* ) echo "Punctuation, whitespace, or other“
;;
esac
#!/bin/bash
echo; echo "Hit a key, then hit return."
read Keypress
case "$Keypress" in
[a-z] ) echo "Lowercase letter“
;;
[A-Z] ) echo "Uppercase letter“
;;
[0-9] ) echo "Digit“
;;
* ) echo "Punctuation, whitespace, or
other“
;;
esac
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read Command
• Allow to read values into variables
• Syntax :
– read VAR1 VAR2
• If there is more input than you are looking for, all the
extras are put in the last variable.
•We can input information into script when executing the script
•Commands :
read
select
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read Command Example
#!/bin/bash
echo "Enter 2 number, I will add them"
read VAR1 VAR2
echo "$VAR1 + $VAR2 = $(($VAR1+$VAR2))"
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select Command
• It is great for creating menu
• Syntax :
select in
do
# commands
done
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select Command
#!/bin/bash
echo
select vday in "MON" "WED" "FRI"
do
echo
echo "Select $vday."
echo
break #if no 'break' here, keeps looping forever.
done
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Functions
• Syntax :
Or
function function_name ()
{
#commands
}
function_name ()
{
#commands
}
–Functions can be called in main script by function’s name.
–It inherits ALL parameters in the main script
–We can change the return code of the function by using return n
command
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Addition functions
• seq x y : set of " from x to y "
Ex:
for vitem in $(seq 1 10)
do
#commands
done
• expr : execute
Ex:
echo ` expr 1 + 1 `
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Deploy
• Step 1 :
– create script file (cat, vi, mc, ...), enter script codes.
• Step 2 :
– add execute permission mode to file ( chmod u+x file )
• Step 3 :
– run it (add script directory to PATH environment or use
absolute path)
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Summary
• Identify Linux shell environments
• Write and configure BASH script using variables
• Flow controls
• Interactive input, functions
Key files, terms, and utilities include:
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
~/.inputrc
function (Bash built-in command)
export
env
set (Bash built-in command)
unset (Bash built-in command)
34
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
Boot, Initialization
Shutdown and Runlevels
Chapter 4
22 Last updated: 26 December 2003
Objectives
• giving commands to the boot loader.
• giving options to the kernel at boot time.
• checking the events in the log files.
• changing to single user mode.
• shutdown or rebooting the system.
• alert users before switching runlevel.
• setting the default runlevel.
LPI topics:
1.106.1 Boot the system
Candidates should be able to guide the system through the booting process.
This includes giving commands to the boot loader and giving options to the
kernel at boot time, and checking the events in the log files.
1.106.2 Change runlevels and shutdown or reboot system
Candidates should be able to manage the runlevel of the system. This objective
includes changing to single user mode, shutdown or rebooting the system.
Candidates should be able to alert users before switching runlevel, and
properly terminate processes. This objective also includes setting the default
runlevel.
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Boot stages
1. BIOS Stage
– BIOS checks the system (POST - Power On Self Test)
2. Bootloader Stage
– The bootloader loads the second stage into memory
3. Kernel Stage
– The Kernel is loaded in to memory
4. Init Stage
– init load all services and user space tools and mounts all
from /etc/fstab
Stage 1:
–POST
•Check the system board
•Check memory
•Check system configuration
•Starts the video operation
•...
–Check bootloader in MBR (Master Boot Record)
Stage 2:
–Lilo
1. Firmware loads the LILO bootsector and executes it.
2. LILO loads its map file
3. The User selects which kernel to boot
4. LILO loads the kernel
5. LILO executes the kernel
4–Grub
GRUB is more advanced bootloader than LILO
1. Firmware loads the GRUB bootsector and executes it.
2. The code loaded using BIOS, with knowledge filesystem
3. GRUB puts up a menu of defined boot options
Stage 3:
–The RAM disk
•load the initial ramdisk
•load the kernel into memory
–nash
•is a very simple script interpreter - not shell
•dedigned to run simple linuxrc scripts
–Kernel stages
•the kernel takes over for bootloader
•the kernel and the initial RAM disk image are already into memory.
Stage 4:
–The final for the boot process is handled by /sbin/init
–Runlevel Scripts
•init call the rc script with an argument that tells it which is the target
runlevel.
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Giving kernel options to the bootloader
• The list of options supported by the current kernel can
be found in
/usr/src/linux/Documentation/kernel-parameters.txt
• The kernel options used are always readable from the
file
/proc/cmdline
• Example: options given to LILO bootloaders
LILO boot: linux aha152x=0x300,10,7
• Means that the Adaptec SCSI adapter is at address 0x300 IRQ 10
and SCSI-ID 7
Before the kernel loads it is normally possible to give kernel options on the boot
loader command line. The can be SCSI adapter addresses, root partition, VGA
terminal mode, default runlevel, etc.
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Giving kernel options to the bootloader
• Kernel options that must always be used can be
entered in the bootloader's configuration file.
• LILO
append=vga=791 hdc=ide-scsi splash=verbose acpi=off
• GRUB
kernel (hd0,2)/boot/vmlinuz.2.4.20 root=/dev/hda3
vga=791 splash=verbose
Note: Options are separated with a space but continuous within the option.
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/etc/modules.conf (or conf.modules)
• Kernels can be of 2 types:
– Monolithic: All device drivers are compiled into the kernel.
– Modular: Some device drivers are compiled as loadable
modules.
• Module configuration file:
– New name: /etc/modules.conf
– Old name: /etc/conf.modules
For modular kernels the modules can be loaded/unloaded manually or automatically.
The parameters needed to define the addresses, irq, dma, etc. for a module, as well as
their system alias names.
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Boot Log files
• As the kernel boots it saves its log messages in an
internal buffer which is readable with the command
dmesg
• most of the system messages including kernel
messages are stored in
– /var/log/messages
• The command
– tail -f /var/log/messages
• allows you to read the last 10 lines of the log file, refreshing it once
a second.
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LiLo configuration file
• This file is read by the LiLo boot loader.
$cat /etc/lilo.conf
prompt
timeout=50
default=linux
boot=/dev/sda
map=/boot/map
image=/boot/vmlinuz-2.4.20-8
label=linux
initrd=/boot/initrd-2.4.20-8.img
read-only
append="root=LABEL=/"
The /etc/lilo.conf file contains options and kernel image information. Popular
LILO directives are:
The amount of time, in tenths of a second, that the system waits for
user input.
timeout
Used following each image, this specifies the device that should be
mounted as the / (root) directory.
root
The root filesystem should initially be mounted read-only.read-only
Prompts the user for input (such as kernel parameters or runlevels)
before booting.
prompt
Directory where the map file is located.map
Provides a label, or name, for each image.label
The file installed as the new boot sector.install
Refers to a specific kernel file.image
The name of the hard disk partition that contains the boot sector.boot
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Grub configuration file
• This file is read by the Grub boot loader.
• Location:
– /boot/grub/grub.conf
– /etc/grub.conf
– /boot/grub/menu.lst
$ cat /etc/grub.conf
default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Linux (2.4.20-8)
root (hd0,0)
kernel /vmlinuz-2.4.20-8 ro root=LABEL=/
initrd /initrd-2.4.20-8.img
<= origin file
<= soft link
<= soft link
Some explanations.
default=0 and timeout=10 means that unless I say otherwise, Grub will load the first
operating system (again counting from zero) - Fedora Core 2 .
splashimage=(hd0,0)/grub/splash.xpm.gz is the full name of the pretty splash image
that is placed behind the Grub menu.
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Runlevels
Reboot6
Full multi-user and GUI mode (redhat)5
unused4
Full multi-user mode3
Multi-user mode (without Network)2
Single user mode1
Shutdown0
DescriptionRunlevel
• The default runlevel is defined in /etc/inittab
id:5:initdefault
– Will start the system in runlevel 5
A runlevel is a software configuration of the system which starts a selected group of
processes.
Runlevels are identified by: 0 1 2 3 4 5 6 S and s
S & s Scripts to run before entering runlevel 1 (single login).
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The /etc/init.d directory
Directories containing symlinks to scripts in
/etc/init.drc[0-6].d
A script used to change runlevels.rc
A script for local startup customizations, started
automatically after the system is running.
rc.local
The startup script launched by init at boot time.rc.sysinit
Names of the links are in the format
[K|S][nn][init.d_name]
–K and S prefixes mean kill and start, respectively.
–The script names starting with S are run with the argument start, and the ones
with K are run with the argument stop.
–Upon entering a new runlevel:
K scripts are run if their equivalent S scripts had been started in the
previous runlevel,
S scripts are run if they had not already been started in the previous
runlevel.
–Therefore on each change of runlevel, the rc script checks the scripts of the
previous and new runlevels to determine which K or S scripts should be run.
–nn is a sequence number controlling startup or shutdown order.
–init.d_name is the name of the script being linked.
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Displaying the current runlevel
– Find the current and previous system runlevel.
• Example
# runlevel
runlevel N 3
• The command runlevel displays the Previous ('N' if None) and the
current
• The previous runlevel was None (After Booting) and present: 3
runlevel
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Changing the runlevel
– Changes the current runlevel.
– /sbin/telinit is linked to /sbin/init.
• Example
# init 6
• restart system.
# init 1
• change to single mode.
telinit
The following arguments serve as directives to telinit:
telinit (or init) can also tell the init process how long it should wait between
sending processes the SIGTERM and SIGKILL signals when shutting down a runlevel
service. The default is 5 seconds, but this can be changed with the -t sec option.
re-execute itself (preserving the state). The /etc/inittab file
is not re-examined. Run level should be one of Ss12345,
otherwise request will be silently ignored.
U or u
switch to single user mode.S or s
re-examine the /etc/inittab file.Q or q
process only those /etc/inittab file entries having runlevel
a,b or c.
a,b,c
switch to the specified run level.0,1,2,3,4,5,6
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/etc/inittab file format
• Each line starting with '#' is a comment.
• Each entry uses one line.
• Each entry's syntax is as follows:
id:runlevels:action:process
Specifies the process (or command) to be executed.process
Describes which action should be taken (see below).action
Lists the runlevels for which the specified action should be taken. The runlevels
field may contain multiple characters for different runlevels. For example,123
specifies that the process should be started in runlevels 1, 2, and 3.
runlevels
A unique sequence of 1-4 characters which identifies an entry in inittab.
Note: For gettys or other login processes, the id field should be the tty suffix of
the corresponding tty, e.g. 1 for tty1. Otherwise, the login accounting might not
work correctly.
id
16
Most common actions:
See man inittab for more info on other actions like:
sysinit, powerwait, powerfail, powerokwait,
powerfailnow, resume, kbrequest, ondemand.
The process will be executed when init receives the SIGINT signal. This
means that someone on the system console has pressed the CTRL-ALT-DEL
key combination. Typically one wants to execute some sort of shutdown either
to get into single-user level or to reboot the machine. Often used to reboot the
machine in many distributions.
ctrlaltdel
An initdefault entry specifies the default runlevel to use. If not specified, init
will ask for a runlevel on the console. The process field is ignored.
initdefault
This does nothing.off
The process will be executed during system boot, while init waits for its
termination (e.g. /etc/rc). The runlevels field is ignored.
bootwait
The process will be executed during system boot. The runlevels field is
ignored.
boot
The process will be executed once when the specified runlevel is entered.once
The process will be started once when the specified runlevel is entered and
init will wait for its termination.
wait
The process will be restarted whenever it terminates (e.g. getty).respawn
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Shutting down the system properly
• Before the system is turned off, it needs:
– shut down every current runlevel service properly;
– unmount all filesystems
• Shutdown
– init 0
– shutdown -h now
– halt
– poweroff
• Reboot
– init 6
– shutdown -r now
Reboot the system. If /etc/inittab is set accordingly ,
pressing will also reboot the system.
shutdown -c
–Cancels the already scheduled shutdown.
Note:
The reboot, poweroff and suspend commands are symbolic links to halt.
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shutdown command
– bring the system down.
• Options
shutdown [options] time
Delay time after killing process (before init)-t {Seconds}
Reboots, does not halt-r
Shuts down without calling init-n
Sends warning / does not shutdown-k
Halts system after shutdown-h
This WILL run fsck on reboot-F
Will not run fsck on the reboot-f
Cancels a shutdown-c
Time format:
Command access rights:
The file /etc/shutdown.allow may contain user names (one per line)
who have permission to run the shutdown command.
At the specified timehh:mm
In 4 minutes4
In 2 minutes+2m
Well...NOW!now
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Summary
• giving commands to the boot loader.
• giving options to the kernel at boot time.
• checking the events in the log files.
• changing to single user mode.
• shutdown or rebooting the system.
• alert users before switching runlevel.
• setting the default runlevel.
Key files, terms, and utilities include:
/var/log/messages
/etc/conf.modules or /etc/modules.conf
dmesg
LILO
GRUB
/etc/inittab
shutdown
init
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1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
The Linux Kernel
Chapter 05
22 Last updated: 26 December 2003
Objectives
• managing a kernel and kernel loadable modules
• loading and unloading modules as appropriate
• customizing the current kernel
• configuration, building a new kernel
• building kernel modules as appropriate.
• installing the new kernel as well as any modules
LPI Topics:
1.105.1 Manage/Query kernel and kernel modules at runtime
Description: Candidates should be able to manage and/or query a kernel and
kernel loadable modules. This objective includes using command-line utilities
to get information about the currently running kernel and kernel modules. It
also includes manually loading and unloading modules as appropriate. It also
includes being able to determine when modules can be unloaded and what
parameters a module accepts. Candidates should be able to configure the
system to load modules by names other than their file name.
1.105.2 Reconfigure, build, and install a custom kernel and kernel modules
Description: Candidates should be able to customize, build, and install a kernel
and kernel loadable modules from source This objective includes customizing
the current kernel configuration, building a new kernel, and building kernel
modules as appropriate. It also includes installing the new kernel as well as
any modules, and ensuring that the boot manager can locate the new kernel
and associated files (generally located under /boot, see objective 1.102.2 for
more details about boot manager configuration).
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The Linux Kernel
• It’s loaded at initial bootup of Linux system, manages
activities : I/O, memory, processes, network
interface,
• Kernel can be built with 2 basic options :
– Device drivers can be built directly into the kernel binary
itself
– Device drivers can be built as external modules to the kernel
Why would you want to build a new kernel ? (newer hardware, faster, more stable, )
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Kernel Version Numbering
• Kernel version numbers:
1. The major number
2. The minor number
3. The micro number (patch number)
4. The patch level , applied by kernel maintainers
• Example
2.4.7-10
View kernel version by command : # uname -r
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Kernel Version Numbering
Kernel version numbering is very structured :
- The minor number is even = stable version
- The minor number is odd = development ver.
- A patch constitutes a more precise measurement of the
kernel version.
To find out what kernel you are running :
# uname -r
Notes: All patchs to the kernel are cumulative. You simply have to obtain and apply
the latest patch for the kernel to be sure you have the most up-to-date patched support.
There are many changes from 2.2 to 2.4
-Itanium and X86-64 AMD Hamer CPU support
-Improve PnP/hot swappable device recognition
-Journaling file systems : ext3, ReiserFS, JFS,..
-
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uname command
– Get name and information about current kernel
• Options
– a Combine all the system information.
– o Print the operating system name.
– r Print the release number of the kernel.
• Example
# uname -a
Linux lpilabs 2.4.20-8 #1 Thu Mar 13 17:54:28 EST 2003
i686 i686 i386 GNU/Linux
uname [options]
Some other option:
–i Print the system's hardware platform.
–m Print the name of the hardware the system is running on.
–n Print the machine's hostname.
–p Print the type of processor (not available on all versions).
–v Print build information about the kernel.
Example:
$ uname -n
lpilabs
$ uname -p
i686
$ uname -v
#1 Thu Mar 13 17:54:28 EST 2003
$ uname -o
GNU/Linux
$ uname -r
2.4.20-8
$ uname -i
i386
$ uname -m
i686
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make command
– Determines which pieces of a large program need to be
recompiled and compile them.
– Executes commands in Makefile to update programs or
module components.
make [targets]
Ref: More about make command and Makefile in LPI-101 course.
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make command
• [targets]
config
• Configure a new kernel line by line on text mode
menuconfig
• Configure a new kernel by text menu
xconfig
• Configure a new kernel by graphic menu (require X Windows)
==> All three methods will save the configuration file as
/usr/src/linux/.config
make menuconfig
–Text based color menus, radiolists & dialogs.
make xconfig
–X windows based configuration tool.
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make menuconfig Interface
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make xconfig Interface
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make command
• [targets]
oldconfig
• Configure a new kernel using an older .config file
clean
• delete *.o files
dep
• Create .depend file
make oldconfig
–Default all questions based on the contents of your existing ./.config file.
–It is often easier to configure a new kernel using an older .config file by
using the make oldconfig command. This will prompt the user only for
new features in the kernel source tree (if the kernel is newer or has been
patched).
make clean
–The make command gets instructions from the Makefile and will build
what is needed. If some files are already present make will use them as is. In
particular files with *.o extensions. To make sure that all the configuration
options in .config are used to rebuild the files needed one has to run make
clean.
make dep
–.depend file containing paths to header files present in the kernel source tree
(/usr/src/linux/include)
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/usr/src/linux/.config
• Verify : allow load modules
# cat .config | grep -i module
# Loadable module support
CONFIG_MODULES=y
• Verify : support ext3
# cat .config | grep -i ext3
CONFIG_EXT3_FS=m
CONFIG_EXT3_INDEX=y
CONFIG_EXT3_FS_XATTR=y
CONFIG_EXT3_FS_XATTR_SHARING=y
CONFIG_EXT3_FS_XATTR_USER=y
CONFIG_EXT3_FS_POSIX_ACL=y
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make command
• [targets]
zlilo
• Make a compressed vmlinuz image and update LILO.
zImage
• Make a simple compressed image
bzImage
• Build an image compressed with gzip.
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make command
• [targets]
modules
• The modules are compiled with make modules.
modules_install
• Copy modules file to the /lib/modules/ directory.
install
• move the new kernel and its associated files into the correct
directories.
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The Source Tree
• Kernel source released as a tarball file
Example:
linux-2.4.31.tar.bz2
• Should NEVER extract to /usr/src/linux/
# tar xjvf linux-2.4.31.tar.bz2 –C /usr/src/
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The Source Tree
Subdirectories in the source tree : /usr/src/linux-2.4.31/
kernel
lib
mm
modules
net
scripts
Documentation
arch
drivers
fs
include
init
ipc
This is the structure that most kernel sources will follow.
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The Modular Kernel
– Store the modules for a particular kernel.
– List of module dependencies
– Is generated by the depmod command
/lib/modules/
/lib/modules//modules.dep
Many components of the Linux kernel may be compiled as modules which the kernel
can dynamically load and remove as required.
The best components to modularize are ones not required at boot time, for example
peripheral devices and supplementary file systems.
Kernel modules are controlled by utilities supplied by the modutils package:
–lsmod
–rmmod
–insmod
–modprobe
–modinfo
# ls /lib/modules/`uname -r`
build modules.generic_string modules.parportmap modules.usbmap
kernel modules.ieee1394map modules.pcimap modules.dep
modules.isapnpmap modules.pnpbiosmap
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The Modular Kernel
– Configuration file for loading kernel modules
– Often contains a list of aliases
• Example
alias char-major-10-181 toshiba
options toshiba tosh_fn=0x62
/etc/modules.conf or
/etc/conf.modules
/etc/modules.conf is consulted for module parameters (IRQ and IO ports) but
most often contains a list of aliases. These aliases allow applications to refer to a
device using a common name. For example the first ethernet device is always referred
to as eth0 and not by the name of the particular driver.
# cat /etc/modules.conf
alias eth0 pcnet32
alias scsi_hostadapter BusLogic
alias sound-slot-0 es1371
post-install sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -L
>/dev/null 2>&1 || :
pre-remove sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -S
>/dev/null 2>&1 || :
alias usb-controller usb-uhci
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The Modular Kernel
– Shows information about all loaded modules
– Handle dependency descriptions for loadable kernel modules
depmod [module]
lsmod
The depmod and modprobe utilities are intended to make a Linux modular kernel
manageable for all users, administrators and distribution maintainers.
# lsmod
Module Size Used by Not tainted
autofs 13268 0 (autoclean) (unused)
pcnet32 18240 1
mii 3976 0 [pcnet32]
ipt_REJECT 3928 6 (autoclean)
iptable_filter 2412 1 (autoclean)
ip_tables 15096 2 [ipt_REJECT iptable_filter]
keybdev 2944 0 (unused)
mousedev 5492 0 (unused)
hid 22148 0 (unused)
input 5856 0 [keybdev mousedev hid]
usb-uhci 26348 0 (unused)
usbcore 78784 1 [hid usb-uhci]
ext3 70784 2
jbd 51892 2 [ext3]
BusLogic 100796 3
sd_mod 13452 6
scsi_mod 107128 2 [BusLogic sd_mod]
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The Modular Kernel
– Installs a loadable module in the running kernel.
– Load the module and any dependent modules listed in
modules.dep
modprobe [module]
insmod [module]
Options for modprobe:
-a, --all
Load all matching modules instead of stopping after the first successful
loading.
-c, --showconfig
Show the currently used configuration.
-C, --config config
Use the file config instead of (the optional) /etc/modules.conf to
specify the configuration. The environment variable MODULECONF can also
be used to select (and override) a different configuration file from the default
/etc/modules.conf (or /etc/conf.modules (deprecated)).
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The Modular Kernel
– Display information about a kernel module
• Options
– a Display the module's author.
– d Display the module's description.
– n Display the module's filename.
– p Display the typed parameters that a module may support.
modinfo [module]
Example: Get infomation from the network module driver.
$ modinfo pcnet32
filename: /lib/modules/2.4.20-8/kernel/drivers/net/pcnet32.o
description: "Driver for PCnet32 and PCnetPCI based ethercards"
author: "Thomas Bogendoerfer"
license: "GPL"
parm: debug int, description "pcnet32 debug level (0-6)"
parm: max_interrupt_work int, description "pcnet32 maximum events handled per interrupt"
parm: rx_copybreak int, description "pcnet32 copy breakpoint for copy-only-tiny-frames"
parm: tx_start_pt int, description "pcnet32 transmit start point (0-3)"
parm: pcnet32vlb int, description "pcnet32 Vesa local bus (VLB) support (0/1)"
parm: options int array (min = 1, max = 8), description "pcnet32 initial option setting(s) (0-15)"
parm: full_duplex int array (min = 1, max = 8), description "pcnet32 full duplex setting(s) (1)"
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The Modular Kernel
– Unloads loadable modules from the running kernel.
• Options
– a Remove all unused modules
– e Save persistent data, do not unload module
– r Remove stacks, starting at the named module
– s Use syslog for error messages
rmmod [module]
Example: unloads the raid0 module.
$ lsmod
Module Size Used by Not tainted
raid0 3880 0 (unused)
autofs 13268 0 (autoclean) (unused)
pcnet32 18240 1
mii 3976 0 [pcnet32]
........
$ rmmod raid0
$
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General Procedure to build kernel
Step 1: Configure kernel’s parameters and build it
make config or
make menuconfig or
make xconfig
make clean; make dep; make bzImage
Step 2: Compile modules
make modules
Step 3: Install modules
make modules_install
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General Procedure to build kernel
Step 4: Copy new kernel to /boot
cp arch/i386/boot/bzImage /boot/vmlinuz-2.4.19-16
Step 5: Copy Sytem.map to /boot
cp Sytem.map /boot/System.map-2.4.19-16
Step 6: Copy .config to /boot
cp .config /boot/config-2.4.19-16
Step 7: Make ramdisk
mkinitrd /boot/initrd-2.4.19-16.img 2.4.19-16
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General Procedure to build kernel
Step 8a: Using : lilo
Add new entry to /etc/lilo.conf
image=/boot/vmlinuz-2.4.19-16
label=linux
initrd=/boot/initrd-2.4.19-16.img
read-only
append="hdc=ide-scsi root=LABEL=/"
Execute
/sbin/lilo –v -t
Notes: You must be run “lilo –v” for update lilo map file.
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General Procedure to build kernel
Step 8b: Using : grub
Add new entry to /etc/grub.conf
title Red Hat Linux (2.4.19-16)
root (hd0,0)
kernel /vmlinuz-2.4.19-16 ro root=LABEL=/ hdc=ide-scsi
initrd /initrd-2.4.19-16.img
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Summary
• managing a kernel and kernel loadable modules
• loading and unloading modules as appropriate
• customizing the current kernel
• configuration, building a new kernel
• building kernel modules as appropriate.
• installing the new kernel as well as any modules
Key files, terms, and utilities include:
depmod
insmod
lsmod
rmmod
modinfo
modprobe
uname
make
make targets:
config
menuconfig
xconfig
oldconfig
modules
install
modules_install
depmod
/lib/modules/kernel-
version/modules.dep
/etc/modules.conf &
/etc/conf.modules
/usr/src/linux/*
/usr/src/linux/.config
/lib/modules/kernel-version/*
/boot/*
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1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
System Logging and Automation
Chapter 06
22 Last updated: 26 December 2003
Objectives
• System logging
– syslogd
– klogd
• Automate tasks
– cron
– at
– anacron
LPI Topics:
1.111.3 Configure and use system log files to meet administrative and security
needs
This objective includes managing the type and level of information logged,
manually scanning log files for notable activity, monitoring log files, arranging
for automatic rotation and archiving of logs and tracking down problems noted
in logs.
1.111.4 Automate system administration tasks by scheduling jobs to run in the
future
Candidate should be able to use cron or anacron to run jobs at regular
intervals and to use at to run jobs at a specific time. Task include managing
cron and at jobs and configuring user access to cron and at services.
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Introduction to System logging
• One integral part of any UNIX system are the logging
facilities.
• The majority of logging in Linux is provided by two
main programs:
– syslogd : logging services to programs and applications.
– klogd : logging capability to the Linux kernel.
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Introduction to System logging
• klogd
– Sends most messages to the syslogd facility
– But will on occasion pop up messages at the console (i.e.
kernel panics).
• syslogd
– Handles the task of processing most messages and sending
them to the appropriate file or device.
– Configuration file: /etc/syslog.conf
By default most logging to files takes place in /var/log/
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Rotating log files
• A common way to keep logging information for a fixed
period is “rotation”.
• Example: rotation policy
#!/bin/sh
cd /var/log
mv logfile.2 logfile.3
mv logfile.1 logfile.2
mv logfile logfile.1
cat /dev/null > logfile
chmod 600 logfile
You keep backup files that are one day old, two days old, and so on. Each day a script
or utility program renames the files to push older data toward the end of the chain.
One common problem is figuring out what to do with all of the log messages. If you
do a lot of logging (particularly if everything is sent to a central server), you can fill
up your filesystem faster than you think. The most obvious and direct solution is to
remove them after a specific length of time or when they reach a particular size.
As its name implies, the goal of the logrotate program is to "rotate" log files. This
could be as simple as moving a log file to a different name and replacing the original
with an empty file.
On the example: every day logfile.7 is lost as logfile.6 overwrites it.
6Logrotate: manage log files:
A logrotate configuration file consists of a series of specifications for groups
of logfiles to be managed.
# Example log rotation policy
errors sa-book@admin.com
rotate 5
weekly
/var/log/messages{
postrotate
/bin/kill –HUP ‘cat /var/run/syslogd.pid
endscript
}
/var/log/samba/*.log{
notifempty
copytruncate
sharedscripts
postrotate
/bin/kill –HUP ‘cat /var/run/syslogd.pid
endscript
}
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Linux log files
– Contains a record of users’ logins and logouts. Should be
rotated .
– Records only the time of last login for each user. No need to
be rotated.
/var/log/wtmp
/var/log/lastlog
For the most part, linux packages send their logging information to files in the
/var/log directory.
Some distribution logs are also stored in /var/adm
Special log files
/var/log/wtmp
Contains a record of users’ logins and logouts, entries that indicate
when the system was rebooted or shut down. Should be rotated.
# who /var/log/wtmp
/var/log/lastlog
It records only the time of last login for each user. Is binary file,
indexed by UID. No need to be rotated because its size stay constant
unless new users log in.
# lastlog
checksecurity utility
runs every day (from /etc/cron.daily/standard) to enumerate the
systems complement of setuid programs( setuid.changes, setuid.today,
setuid.yesterday).
Download (debian):
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Configuring syslogd
• The configuration file /etc/syslog.conf
• Basic format is:
mail.info /var/log/maillog
• Within the selector
– mail : the facility
– info : the level of priority
– /var/log/maillog : the action
selector action
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Facilities
• Supported facilities in Linux:
News subsystemnews
Mail subsystemmail
Spooling subsystemlpr
Linux kernelkern
System server processesdaemon
cron subsystemcron
Login authentication authpriv
Associated SubsystemSyslog Facility
localN Locally-defined syslog facilities N runs from 0 to 7
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priorities
Debugging messagesdebug7
Informational messagesinfo6
notifications, Normal but significant conditionsnotice5
Warning conditionswarning4
Error conditionserr3
Critical conditioncrit2
alerts, Immediate action requiredalert1
emergencies, System unusableemerg0
DescriptionKeywordLevel
Unlike facilities, which have no relationship to each other, priorities are hierarchical.
Possible priorities in Linux are (in increasing order of urgency): debug, info, notice,
warning, err, crit, alert and emerg.
As with facilities, the wildcards * and none.
A priority may be preceded by either or both of the modifiers = and !
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Example
– All messages of severity "info" and above are logged, but
none from the mail, cron or authentication.
.info;mail.none;authpriv.none;cron.none /var/log/messages.info; ail.none;authpriv.none;cron.none /var/log/ essages
Select all priorities except warning
Mail.debug;
mail.!=warning
Select only prio. Info, notice and warningMail.info;mail.!err
Select only messages at info priorityMail.=info
Select mail-related mesg. Of info prio. And higherMail.info
meaningselector
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action
• In practice, most log messages are written to files.
• You can send messages other places too.
Writes the mesg. To all users who are logged in*
Writes the mesg. To user’s screenuser1,user2,
Writes the mesg. To the named pipe fifoname\fifoname
Forward the mesg. To the host at ip address ipaddress@ipaddress
Forward the msg. To syslogd on host name@hostname
Writes the mesg. To file on the local machineFilename
meaningAction
In practice, most log messages are written to files. If you list the full path to a
filename as a line's action in syslog.conf, messages that match that line will be
appended to that file. (If the file doesn't exist, syslog will create it.)
You can send messages other places too. An action can be a file, a named pipe, a
device file, a remote host or a user's screen.
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Config file examples
• Stand-alone machine on a small network.
# emergencies: tell every one who is logged on
*.emerge *
# important messages
*.warning; daemon, auth.info,user.non /var/log/messages
# printer errors
lpr.debug /var/log/lpd-errs
The syslog config file can be customized for each host.
Choose stable machine as your logging server, one that is well secured and does not
have many logins.
Some very large sites may want to add more levels to the logging hierarchy.
Unfortunately syslog retains the name of the originating host for only one hop. If a
host “client” sends some log entries to host “server”, which sends them on to host
“master,” master will see the data coming from server, not from client.
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Config file examples
• a client machine on a larger network
# emergencies tell everyone who is logged on
*.ernerg;user.none *
# Forward important messages to the central logger
*.warning; lpr,local.none @netloghost
daemon,auth.info @netloghost
#cardd logs through facility local1 – send to boulder
local1.debug @boulder.colorado.edu
# keeping printer errors local
lpr.debug /var/log/lpd-errs
# keeping kernel messages local
kern.info /var/log/kern.log
15
Creating a central syslog server
In this example, I will configure our Solaris server environment to send syslog
information to a remote Red Hat Linux 8.0 server.
Changes needed on the syslog server (Red Hat Linux 8.0):
vi /etc/sysconfig/syslog
Change:
SYSLOGD_OPTIONS="-m 0"
To:
SYSLOGD_OPTIONS="-m 0 -r -x"
This change to the syslog daemon enables logging from remote machines and
disables DNS lookups on incoming syslog messages.
Changes needed on the syslog clients (Sun Solaris):
1. vi /etc/syslog.conf
Add the following lines:
# Send a copy to remote loghost
*.info @loghost
auth.* @loghost
Note: make sure that you do not have extra whitespace in the Solaris
syslog.conf file. Separate the facility and severity from the location with either
a single space or with tabs.
2. vi /etc/hosts
Remove any reference to "loghost." By default, Solaris will configure each
host to be its own loghost.
3. Send the syslogd process a SIGHUP signal (kill -HUP pid_of_syslogd).
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at Command
– Execute commands at a specified time or run the
commands on a batch queue.
– Reads commands from stdin or file (with –f option) and
executes them using user’shell.
at [options]
Example: Run ~/mysqcript at 11h:30’
# at 11:30
at> ~/myscript
at>
job 1 at 2005-11-04 11:40
#
The ^D ( ctrl-d ) : sending the end-of-file character to terminate the at
command.
Ctrl+d
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Listing and Deleting at Jobs
– List all jobs.
– Removes job_id
at –l
atq
at –d job_id
atrm job_id
Example
# atq
14 2003-10-31 12:00 a root
# atrm 14
# atq
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crontab
• crontab is located in three places:
/var/spool/cron
• contains user's crontabs
• based on username
/etc/cron.d
• typically used by software installations
/etc/crontab
• maintained by system administrator
cron's uses
–Remove junk files from the system.
–Reload mail aliases
–Reset / Rotate log files
–Synchronize databases
–Checking network resources
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how cron works
• Cron reads all its config files into memory then sleeps.
• Every minute cron wakes
– checks for updates to its config files
– reloads updated files
– executes any tasks scheduled for that minute.
• Output of cron is emailed to the owner of the crontab
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crontab fields
– minute [0-59]
– hour [0-23]
– day [1-31]
– month [1-12]
– weekday [0-6 ] (0=Sunday)
min hr day month wday [usr] cmd
$ cat /etc/crontab
# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly
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crontab format
• Comment lines start with #
• Fields are separated by whitespace
– whitespace is taken literally in the command field
• The command should not be quoted
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crontab format
Treats for any value between 9 and 17. So if placed in day of
month this would be days 9 through 17. Or if put in hours it
would be between 9 and 5.
9-17
Treated as an OR, so if placed in the hours, this could mean
at 2, 4, or 6 o-clock.
2,4,6
Is treated as ever 5 minutes, hours, days, or months.
Replacing the 5 with another numerical value will change this
option.
*/5
Is treated as a wild card. Meaning any possible value. *
ExplanationOptions
Example: Each of the above columns can be in one of the following formats (these
examples are for the minute column):
30
Run command at 30 minutes past the hour.
0-59/10
Run command once every 10 minutes, for the entire hour.
15-30
Run command once every minute, from 15 to 30 minutes past the hour.
0,10,50
Run command at 0 minutes past the hour, 10 minutes past the hour, and
50 minutes past the hour.
*
un command once every minute.
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crontab command
• Maintain crontab files for individual users
• Options
– e : Edit the current cron table
– l : lists the contents of the user's crontab
– r : removes the user's crontab
– u : specifies a username (root only)
• Each user has a personal list of commands kept in the
crontab file, stored in /var/spool/cron/ directory.
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Examples
• To execute myprogram once per day at 6:15 a.m , use
this crontab entry:
15 6 * * * myprogram
• To execute at 6:15 and 18:15 on the 1st and 15th of
the month, use:
15 6,18 1,15 * * myprogram
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System cron table crontab
Users denied use of croncron.deny
Users allowed to use croncron.allow
Users denied use of at (only used if no
at.allow)
at.deny
Users allowed to use at at.allow
Administering at and crontab
• Control and configuration files are kept in /etc
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Administering at and crontab
• /var/spool/cron
– All crontab are stored in the cron spool directory
• /var/spool/at
– All at jobs are stored in the cron spool directory
• Do not edit the files in the spool directories.
– Use the at and crontab utilities to make changes
• Use tail or tail –f to read logfile.
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logrotate command
– Rotates, compresses, and mails system logs.
– Use /etc/logrotate.conf
– After modify the logrotate.conf, run logrotate – f
to take affect.
logrotate [logrotate_config_file]
logrotate is designed to ease administration of systems that generate large
numbers of log files. It allows automatic rotation, compression, removal, and mailing
of log files. Each log file may be handled daily, weekly, monthly, or when it grows
too large.
Normally, logrotate is run as a daily cron job. It will not modify a log multiple
times in one day unless the criterion for that log is based on the log’s size and
logrotate is being run multiple times each day, or unless the -f or -force option is
used.
Sample Contents of /etc/logrotate.conf
# rotate log files weekly
#weekly
# rotate log files daily
daily
# keep 4 weeks worth of backlogs
#rotate 4
# create new (empty) log files after rotating old ones
create
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anacron
• anacron is a task scheduler similar to cron;
• except that it does not require the system to run
continuously.
– It can be used to run the daily, weekly, and monthly jobs
usually run by cron.
• To use the anacron service, you must have:
– the anacron RPM package installed
– the anacron service must be running.
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anacrontab format
• Anacron tasks are listed in the configuration file
/etc/anacrontab.
– period frequency (in days) to execute the command
– delay delay time in minutes
– job-identifier description of the task.
– command command to execute
period delay job-identifier command
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How anacron works ?
• Anacron executes the command specified in the
command field after waiting the number of minutes
specified in the delay field.
• After the task is completed, Anacron records the date
in a timestamp file in the /var/spool/anacron
directory.
For each tasks, Anacron determines if the task has been executed within the period
specified in the period field of the configuration file. If it has not been executed
within the given period, Anacron executes the command specified in the command
field after waiting the number of minutes specified in the delay field.
After the task is completed, Anacron records the date in a timestamp file in the
/var/spool/anacron directory. Only the date is used (not the time), and the value of the
job-identifier is used as the filename for the timestamp file.
Environment variables such as SHELL and PATH can be defined at the top of
/etc/anacrontab as with the cron configuration file.
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anacrontab Example
$ cat /etc/anacrontab
# /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/bin
1 65 cron.daily run-parts /etc/cron.daily
7 70 cron.weekly run-parts /etc/cron.weekly
30 75 cron.monthly run-parts /etc/cron.monthly
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Summary
• syslogd can be configured for both local and remote
logging.
• In the syslog.conf file, every rule consists these
two fields:
– selector field
– action field
• The three major process scheduling utilities:
– at: executes a process once at a specified time
– cron: executes a process repeatedly at specified intervals
– anacron: like cron, but can schedule processes with within
smaller time intervals than what cron allows
Key files, terms, and utilities include:
/etc/syslog.conf
/var/log/*
/etc/anacrontab
/etc/at.deny
/etc/at.allow
/etc/crontab
/etc/cron.allow
/etc/cron.deny
/var/spool/cron/*
at
atq
atrm
crontab
logrotate
tail -f
1Linux Junior Level Administration - LPI 102
1 2004, SaigonCTT All rights reservedLast updated: 26 December 2003
Maintain System
Chapter 07
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Objectives
• Setting the system date and time
• Setting the BIOS clock to the correct time in UTC
• Configuring the correct timezone for the system
• Configuring the system to correct clock drift to match
NTP clock.
• Dumping a raw device to a file or vice versa
• Performing partial and manual backups
LPI Topics:
1.111.5 Maintain an effective data backup strategy
Tasks include dumping a raw device to a file or vice versa, performing partial
and manual backups, verifying the integrity of backup files and partially or
fully restoring backups.
1.111.6 Maintain system time
Tasks include setting the system date and time, setting the BIOS clock to the
correct time in UTC, configuring the correct timezone for the system and
configuring the system to correct clock drift to match NTP clock.
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Time clocks under Linux
• Linux uses two clocks:
– Hardware Clock:
• RTC, RealTimeClock, CMOS Clock, BIOS Clock.
– Software Clock:
• System Clock. Runs via the system timer interrupt.
Hardware Clock:
– Runs independent of the Operating System and runs even when the computer
is turned OFF, as long as the CMOS battery lasts.
Software Clock:
–Counts the number of seconds since 1st. Jan. 1970. Is the main clock under
Linux. At boot time it reads the hardware clock and continues alone from
there.
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Clock control programs
• Under Linux 2 main programs are used to control the
2 clocks.
– Controls the Hardware Clock
– Controls the System Clock
hwclock
date
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Time settings and zones
• There are 2 standard ways to set the clock.
– Local time
• Time at this geographic location
– UTC
• Universal Co-ordinate Time. Normal way of setting the time from
which a time zone offset is given to calculate the Local Time.
UTC is Coordinated Universal Time, GMT is Greenwich Mean Time.
Greenwich (pronounced 'grenn-itch' ) is a town, now part of the south eastern urban
sprawl of London, on the south bank of the River Thames in the London Borough of
Greenwich.
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Setting the time in Linux
• The procedure is relatively simple:
1. Set the Hardware clock to UTC via the BIOS setup.
2. Set the environment variable TZ to the proper time zone:
3. To tell Linux that our Hardware clock and system clock are
set to UTC run:
tzselect
hwclock --utc --hctosys
Alternative step 2:
Use the program tzconfig which will set a symbolic link in the form of:
ln -s /usr/share/zoneinfo/Europe/Berlin /etc/localtime
$ tzselect
Please identify a location so that time zone rules can be set correctly.
Please select a continent or ocean.
1) Africa
5) Asia
#? 5
Please select a country.
15) Indonesia 32) Nepal 49) Vietnam
#? 49
The following information has been given:
Vietnam
Therefore TZ='Asia/Saigon' will be used.
Local time is now: Wed Sep 28 10:58:46 ICT 2005.
Universal Time is now: Wed Sep 28 03:58:46 UTC 2005.
Is the above information OK?
1) Yes
2) No
#? 1
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hwclock
– This program is used to display or set the Hardware clock.
• Options
--set
• Set the Hardware Clock to the time given by the --date option.
--systohc
• Set the Hardware Clock to the current System Time.
--utc
• Indicates that the Hardware Clock is kept in Universal Coordinated
Time.
hwclock [option]
Options:
--show
Read the Hardware Clock and print the time to Standard Output. The
time shown is always in local time, even if you keep your Hardware
Clock in Coordinated Universal Time (UTC).
--hctosys
Set the System Time from the Hardware Clock. Also set the kernel's
timezone value to the local timezone as indicated by the TZ
environment variable and/or /usr/share/zoneinfo. This is a
good option to use in one of the system startup scripts.
--adjust
Add or subtract time from the Hardware Clock to account for systemic
drift since the last time the clock was set or adjusted.
--localtime
Indicates that the Hardware Clock is kept in Local Time. It is your
choice whether to keep your clock in UTC or local time, but nothing in
the clock tells which you've chosen. So this option is how you give that
information to hwclock.
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date
– This program is used to show or set the System time.
• Options:
– +text_and_metacodes
• Allows control of the display of the current time /and/or date.
• Example:
# date "+It is now %H Hours and %M Minutes"
It is now 14 Hours and 33 Minutes
date [options]
Interpreted sequences are:
day of year (001..366)%j
hour (01..12)%I
hour (00..23)%H
same as %b%h
the 4-digit year corresponding to the %V week number%G
the 2-digit year corresponding to the %V week number%g
same as %Y-%m-%d%F
day of month, blank padded ( 1..31)%e
date (mm/dd/yy)%D
day of month (01..31)%d
century (year divided by 100 and truncated to an integer) [00-99]%C
locale's date and time (Sat Nov 04 12:02:33 EST 1989)%c
locale's full month name, variable length (January..December)%B
locale's abbreviated month name (Jan..Dec)%b
locale's full weekday name, variable length (Sunday..Saturday)%A
locale's abbreviated weekday name (Sun..Sat)%a
a literal %%%
9By default, date pads numeric fields with zeroes. GNU date recognizes the following
modifiers between `%' and a numeric directive.
‘-’ (hyphen) do not pad the field
‘_’ (underscore) pad the field with spaces
Time Parameters
MMDDhhmm
Set the System time to a specific value
MMDDhhmmYYYY.[ss]
Set the System time to a specific extended value.
Note: In the file /etc/adjtime the correction factor can be saved to keep
the clock as accurate as possible.
time zone (e.g., EDT), or nothing if no time zone is determinable%Z
RFC-822 style numeric timezone (-0500) (a nonstandard extension)%z
year (1970...)%Y
last two digits of year (00..99)%y
locale's time representation (%H:%M:%S)%X
locale's date representation (mm/dd/yy)%x
week number of year with Monday as first day of week (00..53)%W
day of week (0..6), 0 represents Sunday%w
week number of year with Monday as first day of week (01..53)%V
week number of year with Sunday as first day of week (00..53)%U
day of week (1..7) , 1 represents Monday%u
time, 24-hour (hh:mm:ss)%T
a horizontal tab%t
second (00..60), the 60 is necessary to accommodate a leap second%S
seconds since `00:00:00 1970-01-01 UTC' (a GNU extension)%s
time, 24-hour (hh:mm)%R
time, 12-hour (hh:mm:ss [AP]M)%r
locale's lower case am or pm indicator (blank in many locales)%P
locale's upper case AM or PM indicator (blank in many locales)%p
nanoseconds (000000000..999999999)%N
a newline%n
minute (00..59)%M
month (01..12)%m
hour ( 1..12)%l
hour ( 0..23)%k
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Network Time Service
• This service is used to set the client clocks to a very
precise clock.
• The service compensates for the delay introduced by
TCP.
• Protocol:
– NTP
• Daemon
– ntpd
Methods:
1. Cron job queries the time server using the ntpdate program.
2. Local daemon (ntpd or xntpd) runs on client and polls the time server.
Note: This solution transforms the client to a Time Server.
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ntpdate
– This program connects with a Time Server and sets the
System time.
– Normally it is regularly called from a cron job.
• Example:
10 * * * * root /usr/sbin/ntpdate ntp3.fau.de
ntpdate TimeServerName
Note: A list of time servers on the Internet is located at:
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ntpd or xntpd
• These daemons poll one or more Time Server(s) every
5 minutes and sets the system time.
• Configuration file:
/etc/ntp.conf
• Example contents:
server ntp3.fau.de
driftfile /etc/ntp.drift
This driftfile will store the local Hardware Clock drift and will be used at boot time to
set local System Clock to a more accurate time till a connection to a Time Server is
achieved.
Note1: If the local time has drifted off more than 1000 seconds then a syslog message
is generated and the clock must be set manually.
Note 2: It is also possible to use both methods: ntpd and ntpdate at the same time.
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Types of backups
• Full Backup
– Backs up all files
• Differential Backup
• Incremental Backup
Full backup Differential Backup
Incremental Incremental Incremental
Backs up all files, regardless of whether they were previously backed up or not. This
method uses the most media space. In this case it is recommended to use compression
like gzip or other methods to reduce the media space needed.
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Differential Backup
• Saves only files that have been modified or created
since the last Full Backup.
• Advantages:
– Only the full backup and the last good differential backup
are needed to restore the whole of the data.
• Disadvantages:
– Takes longer to make than incremental backups and needs
larger media.
Notes: Normally a Full backup is made and then regular differential Backups are
performed.
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Incremental Backup
• Each backup is an increment since the most recent
backup (Full, Differential or previous Incremental).
• Advantages:
– Shorter to make than the differential backups and needs
smaller media size.
• Disadvantages:
– All of the incremental backups, up to the last known good
one, and the full backup are needed for restoring.
– If one of the incremental backups has some media fault, the
entire backup may be unreliable.
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Restoring data
• With differential backups:
1. Read the full backup
2. Read last good differential backup.
• With incremental backups:
1. Read the full Backup
2. Read sequentially each incremental backup up to the last
good one.
With differential backups:
–The Full backup and the last good differential backup is needed.
With incremental backups:
–The Full backup and ALL of the incremental backup are needed.
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Backup media devices files
May be an ATAPI Zip or other removable disk/dev/hdx
First floppy disk drive/dev/fd0
First floppy-controller tape drive/dev/ft0
First SCSI Tape Drive/dev/st0
To create backups, external media devices are needed. On slide show some common
ones used under Linux.
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Basic backup programs
– Recursively creates archives of files and directories including
file properties.
• Basic Mode options
– c Create a new archive.
– t List the content of the archive
– x Extract files from the archive.
tar
Basic mode options
f ta
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