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ON eee (ola eal dl Aire
OS Lab Presentation
Hossein Joukar 9031006 - Ehsan Edalat 9031066
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ا ا
یت ون کر
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ا ادك
> It is necessary for regular users to run a command as if
they were root.
deh Uhl وروت رها
>» This command changes the UID and GID of the existing
6۲
>» The syntax for the su command is this:
su option username arguments
su -c 'Is /home/bob' - bob
ea or re ate ced need oo ence oe ene een ey
Pr een ante
> To return to the regular users’ identity
Lams
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a OLAS ادك
> It gives to the certain users only a few superuser
permissions.
> The list of authorized users is kept in /etc/sudoers
> Sudo will prompt for a password and then check the
/etc/sudoers.
> Sample:
< 500 66و10 1
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GO OG GOOO
> SU is a command that root user with his own password
can perform all commands but SUDO is a command
that regular user with his own password can perform
especial commands that mention in /usr/sbin/visudo.
> Users can add or remove from /usr/sbin/visudo in
format that mention below:
Ok emo (ne mee a)
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(Groups
> /etc/group
> The custom is to use GIDs of 500 or more for regular
users and less for administrations or special program.
> Groupname:password:gid:users
root:x:0:root
bin:x:1:root,bin,daemon
> Special group
تا تا ها
te iene ۱
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Phe Password Pile
> /etc/passwd
> It is the database file for all users on the system.
۱ a a
> * in password means disable.
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حل« سوحه ”) سدلككحا)
2 0 at 1 oy-To1 <=) (=)
> /etc/shadow
> It is considered to use the encrypted passwords found
in /etc/passwd.
> Only x or * appears in the passwprd field of
/etc/passwd..
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حل« سوحه ”) سدلككحا)
> Advantages of shadow over the traditional mode
» Shadow passwords improve system security by moving
encrypted password hashes from the world-readable
/etc/passwd file to /etc/shadow, which is readable only by
۱
» Shadow passwords store information about password
aging.
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CNN Des aNd 5
> The user’s login name
> The encrypted password
> The number of days since jan 1970
> The number of days before the the password can
be changed
> The number of days before the password is to
expire that the user is warned it will expire.
> The number of days after the password expires
the account is disabled.
> The number of days since jan 1 1970 that
account has been disabled.
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4 Viexercd Directory 5
> When each user is created, a home directory is
created for him (/nome/<username>).
> The set of files that initially are used to populated this
home directory are kept in /etc/skel.
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۱۱ مر Meal 1
> The User Accounts configuration tool allows you to
view, modify, add, and sae local users. To run the
the User Accounts مع
> By default, the tool only allows you to change certain
settings regarding yo count. This is because only
the root user is allowed to configure users and groups.
To unlock the configuration یا و۱ 05
1۱ رز are
corner of the window, and provide the correct
password when prompted.
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Osicry 00 eae cae Be
AL Settings
Jaromir Hradilek
Standard
English
Login Options
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فم
Create new account
Account Ty Standard
Fullname | Eva Kopalova
Username | ekopatova
Cancel
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فم
De you want to keep Eva Kepalova's files?
Itis possible to keep the home directory, mail spool and temporary files around
when deleting @ user account.
| Keep Files Cancel,
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you to view,
ind groups in the
application, either
Groups from
-config-users at a
lave superuser
عونا ع1 <-
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Osicry the Oser (ON ene ci ae
> Fedora reserves user and group IDs below 1000 for
system users and groups. By default, the User
Manager does not display the system users. To view all
users and groups, select Edit > Preferences to open
the Preferences dialog box, and clear the Hide system
users and groups check box.
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Apply fitter
Home Directory
مهدجه
قناماة م اء لع وم
Refresh
Full Name Login Shell
Jaromir Hradilek /bin/bash
Ibirvbash
Fle Edit Help
B® ©
Add User AddGroup Propert
Users | Graups
User Name User ID ¥ | Primary Group
1000
1001
jnradiek عافد
ekopalove ekopalova
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فم
Conti Password: [>= ۱
Logi Sha دا سم
1 Create home drectory
Home Directory: |snome/ekopatova
© Create a private group for the
Specify user 1D manually
1 Specity group 1D manually
۳
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CON NNO Ua Dic
> To specify a user ID for the user, select Specify user ID
manually. If the option is not selected, the next
available user ID above 1000 is assigned to the new
user. Because Fedora reserves user IDs below 1000 for
system users, it is not advisable to manually assign
۱۱۳ روت
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CONN NNR OD UPA (eae od
Group Name: | publishers
“) Specify group ID manually:
Cancel
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Properties
عه
Full Name دجم
Password: 0 "۱
Confirm Password, |***** ۱
6 9 ست:
Login Shell: {fbinibash -[
Cancet_||
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Group Data ۱ Group Users
Select the users to join this group:
cancel || 0K
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Oser ۱۹۱2۹ ac ri ea OA ARN ed
> useradd [option] user name
تس هه
< اعلرعدن
م
ع5 ها iCele
كا 2
> groupadd [option] group_name
تال سس هه
> groupdel
< منامعو ة عنعاءم
۲ ۵
انا 0
8 کیره
Pern ل ل uy
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4
> useradd [option] user name
>» Options:
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> -d home_directory
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disabled. If 0 is specified, the account is disabled immediately
after the password expires. If -1 is specified, the account is not
معاطهدال ع5 ucm re eee Ken ice
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4
> Options:
> -g group_name
> Group name or group number for the user's default group.
> -G group _list
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>» Options:
> -p password
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۱۹ 7
> groupadd [option] group_name
> Options:
۲ او و
> Group ID for the group, which must be unique and greater than
ووو
> -p, --password password
۱ h ceo homeo
> -o, --non-unique
۱ ل oeicon
”ند صمي
note ct met رها
ل 0
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> To configure password expiration for a user from a shell
prompt, run the following command as root:
> chage [options] username
> Options:
> -d days
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account is not locked after the password expires.
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الهس <
> Sends a message to the terminals of all user
connected to the system.
> talk
> Allows two-way communication between any two
eles
> write
> Send a message to a user
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لك 2
«- لمصطء
> Change file access permission
> chown
» Change file owner or group
> chroot
>» Run command with special root directory
صفحه 32:
Thanks for your attention
Users & Groups in Linux
OS Lab Presentation
Hossein Joukar 9031006 – Ehsan Edalat 9031066
Managing Users
2
Each system has two kinds of users:
Superuser (root)
Regular user
Each user has his own username, password, and
permissions that can only be assigned by the user.
Group is set of users that has permission to access
special files(read, write, execute) and that owner and
the root can manage level of accesses to them.
All users have a user ID (UID) and a group ID (GID).
The su Command
3
It is necessary for regular users to run a command as if
they were root.
The su means substitute user.
This command changes the UID and GID of the existing
user.
The syntax for the su command is this:
su option username arguments
su -c 'ls /home/bob' – bob
the following command switches to user bob's account and produces a list of the contents
of bob's home directory
To return to the regular users’ identity
exit
The sudo Command
It gives to the certain users only a few superuser
permissions.
The list of authorized users is kept in /etc/sudoers
Sudo will prompt for a password and then check the
/etc/sudoers.
Sample:
Sudo fdisk /dev/hda1
4
SU VS SUDO
5
SU is a command that root user with his own password
can perform all commands but SUDO is a command
that regular user with his own password can perform
especial commands that mention in /usr/sbin/visudo.
Users can add or remove from /usr/sbin/visudo in
format that mention below:
User_name Machine_name=(Effective_user) command
Groups
6
/etc/group
The custom is to use GIDs of 500 or more for regular
users and less for administrations or special program.
Groupname:password:gid:users
root:x:0:root
bin:x:1:root,bin,daemon
test:x:500:
Special group
Allow these services to manage their own files with permissions
that restrict other users from them.
The Password File
/etc/passwd
It is the database file for all users on the system.
Username:password:uid:gid:comment:homedir:shell
* in password means disable.
7
Shadow Passwords
8
shadow-utils package
/etc/shadow
It is considered to use the encrypted passwords found
in /etc/passwd.
Only x or * appears in the passwprd field of
/etc/passwd..
Shadow Passwords
9
Advantages of shadow over the traditional mode
Shadow passwords improve system security by moving
encrypted password hashes from the world-readable
/etc/passwd file to /etc/shadow, which is readable only by
the root user.
Shadow passwords store information about password
aging.
Shadow Password Fields
1
0
The user’s login name
The encrypted password
The number of days since jan 1970
The number of days before the the password can
be changed
The number of days before the password is to
expire that the user is warned it will expire.
The number of days after the password expires
the account is disabled.
The number of days since jan 1 1970 that
account has been disabled.
User’s Home Directory
1
1
When each user is created, a home directory is
created for him (/home/<username>).
The set of files that initially are used to populated this
home directory are kept in /etc/skel.
Using the User Accounts Tool
1
2
The User Accounts configuration tool allows you to
view, modify, add, and delete local users. To run the
tool, selectApplications → System Tools → System
Settings from the Activities menu and click
the User Accounts icon.
By default, the tool only allows you to change certain
settings regarding your account. This is because only
the root user is allowed to configure users and groups.
To unlock the configuration tool for all kinds of
changes, click the Unlock button in the top-right
corner of the window, and provide the correct
password when prompted.
Using the User Accounts Tool
1
3
Adding a New User
1
4
Removing a User
1
5
Using the User Manager Tool
1
6
The User Manager application allows you to view,
modify, add, and delete local users and groups in the
graphical user interface. To start the application, either
select Applications → Other → Users and Groups from
the Activities menu, or type system-config-users at a
shell prompt. Note that unless you have superuser
privileges, the application will prompt you to
authenticate as root.
Using the User Manager Tool
1
7
Fedora reserves user and group IDs below 1000 for
system users and groups. By default, the User
Manager does not display the system users. To view all
users and groups, select Edit → Preferences to open
the Preferences dialog box, and clear the Hide system
users and groups check box.
Viewing Users and Groups
1
8
Adding a New User
1
9
Adding a New User
2
0
To specify a user ID for the user, select Specify user ID
manually. If the option is not selected, the next
available user ID above 1000 is assigned to the new
user. Because Fedora reserves user IDs below 1000 for
system users, it is not advisable to manually assign
user IDs 1–999.
Adding a New Group
2
1
Modifying User Properties
Properties
2
2
Modifying Group Properties
2
3
User Management Commands
useradd [option] user name
userdel
Delete a group
groupmod
Create a new group
groupdel
Modify a user account
groupadd [option] group_name
Delete a user
usermod
Create a new user
Modify a group
grpck
Verify the integrity of the system authentication information.
2
4
Adding a New User
useradd [option] user name
Options:
-c ‘comment’
Home directory to be used instead of default /home/username/.
-e date
comment can be replaced with any string. This option is
generally used to specify the full name of a user.
-d home_directory
2
5
Date for the account to be disabled in the format YYYY-MM-DD.
-f days
Number of days after the password expires until the account is
disabled. If 0 is specified, the account is disabled immediately
after the password expires. If -1 is specified, the account is not
be disabled after the password expires.
Adding a New User
2
6
Options:
-g group_name
-G group_list
Create the home directory if it does not exist.
-M
List of additional (other than default) group names or group
numbers, separated by commas, of which the user is a
member.
-m
Group name or group number for the user's default group.
Do not create the home directory.
-N
Do not create a user private group for the user.
Adding a New User
2
7
Options:
-p password
-r
Create a system account with a UID less than 1000 and
without a home directory.
-s
The password encrypted with crypt.
User's login shell, which defaults to /bin/bash.
-u uid
User ID for the user, which must be unique and greater than
999.
Adding a New Group
groupadd [option] group_name
Options:
-g gid
Use this encrypted password for the new group.
-o, --non-unique
Group ID for the group, which must be unique and greater than
999.
-p, --password password
2
8
Allow to create groups with duplicate.
-f, --force
When used with -g gid and gid already exists, groupadd will
choose another unique gid for the group.
configure password
2
9
To configure password expiration for a user from a shell
prompt, run the following command as root:
chage [options] username
Options:
-d days
Specifies the number of days since January 1, 1970 the
password was changed.
-I days
Specifies the number of inactive days after the password
expiration before locking the account. If the value is 0, the
account is not locked after the password expires.
Communicating With Users
wall
talk
Sends a message to the terminals of all user
connected to the system.
Allows two-way communication between any two
users.
write
Send a message to a user
3
0
Some Useful Command
chmod
chown
Change file access permission
Change file owner or group
chroot
Run command with special root directory
3
1
3
2
Thanks for your attention
