Users & amp; Groups in Linux

Users & amp; Groups in Linux

اسلاید 1: Users & Groups in LinuxOS Lab PresentationHossein Joukar 9031006 – Ehsan Edalat 9031066

اسلاید 2: Managing UsersEach system has two kinds of users:Superuser (root)Regular userEach 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).2

اسلاید 3: The su CommandIt 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 argumentssu -c ls /home/bob – bobthe following command switches to user bobs account and produces a list of the contents of bobs home directoryTo return to the regular users’ identity exit3

اسلاید 4: The sudo CommandIt gives to the certain users only a few superuser permissions.The list of authorized users is kept in /etc/sudoersSudo will prompt for a password and then check the /etc/sudoers.Sample:Sudo fdisk /dev/hda14

اسلاید 5: SU VS SUDOSU 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) command5

اسلاید 6: Groups/etc/groupThe custom is to use GIDs of 500 or more for regular users and less for administrations or special program.Groupname:password:gid:usersroot:x:0:rootbin:x:1:root,bin,daemontest:x:500:Special groupAllow these services to manage their own files with permissions that restrict other users from them.6

اسلاید 7: The Password File/etc/passwdIt is the database file for all users on the system.Username:password:uid:gid:comment:homedir:shell* in password means disable.7

اسلاید 8: Shadow Passwords shadow-utils package/etc/shadowIt is considered to use the encrypted passwords found in /etc/passwd.Only x or * appears in the passwprd field of /etc/passwd..8

اسلاید 9: Shadow PasswordsAdvantages of shadow over the traditional modeShadow 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.9

اسلاید 10: Shadow Password FieldsThe user’s login nameThe encrypted passwordThe number of days since jan 1970The number of days before the the password can be changedThe 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.10

اسلاید 11: User’s Home DirectoryWhen 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.11

اسلاید 12: Using the User Accounts Tool 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.12

اسلاید 13: Using the User Accounts Tool13

اسلاید 14: Adding a New User 14

اسلاید 15: Removing a User 15

اسلاید 16: Using the User Manager Tool 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.16

اسلاید 17: Using the User Manager Tool 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.17

اسلاید 18: Viewing Users and Groups 18

اسلاید 19: Adding a New User 19

اسلاید 20: Adding a New User 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 1–999.20

اسلاید 21: Adding a New Group 21

اسلاید 22: Modifying User Properties Properties22

اسلاید 23: Modifying Group Properties 23

اسلاید 24: User Management Commandsuseradd [option] user nameCreate a new useruserdel Delete a userusermod Modify a user accountgroupadd [option] group_nameCreate a new groupgroupdelDelete a groupgroupmodModify a groupgrpckVerify the integrity of the system authentication information.24

اسلاید 25: Adding a New Useruseradd [option] user nameOptions:-c ‘comment’comment can be replaced with any string. This option is generally used to specify the full name of a user.-d home_directoryHome directory to be used instead of default /home/username/.-e dateDate for the account to be disabled in the format YYYY-MM-DD.-f daysNumber 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.25

اسلاید 26: Adding a New UserOptions:-g group_nameGroup name or group number for the users default group.-G group_listList of additional (other than default) group names or group numbers, separated by commas, of which the user is a member.-mCreate the home directory if it does not exist.-MDo not create the home directory.-NDo not create a user private group for the user.26

اسلاید 27: Adding a New UserOptions:-p passwordThe password encrypted with crypt.-rCreate a system account with a UID less than 1000 and without a home directory.-sUsers login shell, which defaults to /bin/bash.-u uidUser ID for the user, which must be unique and greater than 999.27

اسلاید 28: Adding a New Groupgroupadd [option] group_nameOptions:-g gidGroup ID for the group, which must be unique and greater than 999.-p, --password passwordUse this encrypted password for the new group.-o, --non-uniqueAllow to create groups with duplicate.-f, --forceWhen used with -g gid and gid already exists, groupadd will choose another unique gid for the group.28

اسلاید 29: configure passwordTo configure password expiration for a user from a shell prompt, run the following command as root:chage [options] usernameOptions:-d daysSpecifies the number of days since January 1, 1970 the password was changed.-I daysSpecifies 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.29

اسلاید 30: Communicating With UserswallSends a message to the terminals of all user connected to the system.talkAllows two-way communication between any two users.writeSend a message to a user30

اسلاید 31: Some Useful CommandchmodChange file access permissionchownChange file owner or groupchrootRun command with special root directory31

اسلاید 32: Thanks for your attention 32