Week7. linux. operating. system. .ppt

© 2006 ITT Educational Services Inc.
Linux Operating System :: Unit 3 :: Slide 1
Downloading and Installing Software
• yum
• pirut
• Bit Torrent
• rmp

yum
• Yellow Dog Updater, Modified
• Ready to use as installed
• Works with rpm packages
• Download from repositories

• yum update
• yum install whatever

pirut
• graphical interface to add or remove software

BitTorrent
• P2P – peer to peer
• Does not use a dedicated server
• tracker – server that allows client to communicate
with one anther
• peer – client that has downloaded part of the
BitTorrent file
• seed – has whole file and acts as an addition
source for the BitTorrent file
• collectively called a swarm

In this animation, the colored bars beneath all of the 7 clients in
the upper region above represent individual pieces of the file.
After the initial pieces transfer from the seed (large system at
the bottom), the pieces are individually transferred from
client to client. The original seeder only needs to send out
one copy of the file for all the clients to receive a copy.

RPM
• installs
• uninstalls
• upgrades
• queries and verifies rpm packages
• used by many different distributions
• keeps track of installed packages, version ,where
software packages are installed and the
dependencies between the packages

• software-2.3.4.rpm
• # rpm -i software-2.3.4.rpm
 to install
• # rpm -U software-2.3.4.rpm
 to upgrade

Chapter 16
• Administration Tasks

Figure 16-1 The User Manager window,
Users tab

Figure 16-2 The User Properties window,
User Data tab

Managing Users and Groups
•One of the key administrative tasks with Linux is
managing users and groups.
•The primary reason for user accounts is to verify the
identity of each individual using a computer system.
 A secondary reason for user accounts is to permit
the per-individual tailoring of resources and
access privileges.
• Resources can include files, directories, and
devices. Controlling access to these resources
is a primary task of an administrator

Groups tie together users that have a
common purpose.
 an organization may have persons responsible for
accounts payable and others responsible for payroll.
• By placing the user accounts in an accounts payable group
then common permissions can be given to all the members of
that group.
• Members of the accounts payable group would not have
access to the information and resources of the payroll group.
Users within the same group have the same read, write. or
execute privileges of group resources.

etc
•Several files are used when creating users in Linux. The
following are a few most commonly used.
/etc/passwd
/etc/shadow
/etc/group

/etc/passwd
• The /etc/passwd file contains the user ID, and
default home directory. Because this file is used
by many tools it needs to be readable by any user.
• To view the /etc/passwd file use the less
command.
less /etc/passwd
 The /etc/passwd file is a group of fields separated with a
colon (:). They are username, password (shown as an x),
numeric user ID, numeric group ID, full name, user’s
home directory, and user’s shell account.

/etc/shadow
•The /etc/shadow file contains the encrypted passwords and other password
information.
 This file is viewable by the root user only.
•To view the /etc/shadow file use the following commands:
su – root
tail /etc/shadow
•The /etc/shadow file is a group of fields separated with a colon (:). They are:
 Username
 password (13 characters encrypted)
 the number of days since the password was last changed
 the number of days before the password may be changed
 the number of days to warn a user of an expiring password
 the number of days after a password expires that account is disabled
 the number of days since an account has bee disabled
 a reserved field for possible future use.

Adding a User 1
•Use the useradd command to add a user. The syntax of the command
is displayed by typing the command alone.
useradd
•The most basic command to add a user named John Smith with and
user ID of jsmith is the following:
useradd jsmith
•If you view /etc/passwd after the add you will see that jsmith has been
added.
jsmith:x:501:501::/home/jsmith:/bin/bash
id:password(shadowed):Full Name:homeDir:shell
 The full name can be added with the –c option. useradd –c “John
Smith” jsmith

Adding a User 2
•When a user is added the home directory is not created automatically. It is
assigned but not created until the user logs in the first time. To force the
home directory to be created use the –m option. The following command will
create the jsmith user and create the associated home directory:
useradd –c “John Smith” –m jsmith
•View the jsmith user home directory with the command:
ls /home/directory
•Any files and directories that are in the /etc/skel directory are automatically
copied into the newly created home directory. If /etc/skel has no files or
directories (the default) then nothing is created.
•The /etc/skel directory on this Linux system has a Documents directory and a
Welcome file.

Adding a User 3
•A look at the /etc/shadow file shows that jsmith was added but a password
has not been assigned. The command to add a password is passwd. As root
you can change the password for jsmith with the following command:
passwd jsmith
•You will be asked to type the password and then repeat it to ensure it was
typed correctly. The root user can change any user password. A user can
change their own password by typing passwd without a user ID.
•passwd has options to configure the minimum password lifetime, maximum
password lifetime, and other options.

Deleting a User
•Deleting a user is done as the root user with the userdel command. To
delete the user jsmith use the command:
userdel jsmith
•Userdel has one option, -r, which removes the user’s home directory as well
as the account. To remove jsmith and the associated home directory,
/home/jsmith, use the following command:
userdel –r jsmith
•Once a user’s home directory is removed it would have to be restored from
backup to recover it.
•There may be orphaned files – files that are not associated by a valid user –
when you delete a user
 Example: jsmith was storing some files in /tmp. Those files are not deleted
when the user jsmith is removed. Those files in /tmp are now orphaned.

Adding a Group
•The mail file for groups is the /etc/group file. The file is a group of fileds that
describe the group and who is a member of it. The fields in order are the
group name, password (not used), numeric ID, and then a list of members
separated by a comma.
•A group is used to assign rights and permissions to users. For example, if
you have several files that should be made available to users in the Accounts
Payable department you could create an Accounts Payable group then add
users to the group. Once the group is populated then the permissions of the
file or directory can be changed to allow access by the group.
•To add a group use the groupadd command.
groupadd AccountsPayable

Assigning Users to a Group
•The usermod command is used to add users to a group.
 It also has options to change the home directory, change the shell, and other
values.
•To use usermod to add users jsmith and jdoe to the AccountsPayable group
type the following:
usermod –G AccountsPayable jsmith
usermod –G AccountsPayable jdoe

Changing Group Permissions
•Groups can be used to assign privileges to resources, such as a directory.
 to change the group to AccountsPayable. This is accomplished with the
following command:
chgrp –R AccountsPayable AP
 Where –R causes it to recursively affect files and directories within the AP
directory, AccountsPayable is the new group, and AP is the name of the
directory.
 Permissions for group are then changed to give full read/write/execute access
with the chmod command.
chmod 775 AP

Week7. linux. operating. system. .ppt

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