Session7 Theory

5/20/2018 Session7 Theory

1/11ADVANTAGE PROChennais Premier Networking Training Centre

Useradd :

To create a new user account and login directory for that

new account.

Useradd will create new entries in system files.Syntax

useradd [options] [user]

Options

-c Comment field.

-d Home directory

-e Account expiration date.

useradd command



Passwd comand

Passwd:

The passwd command is used to set the password for the user.

Syntax

passwd Example:

#passwd tom

- this example set password for tom user.

#passwd

- this example set password for current loin user.



Userdel command

Userdel

The userdel command is used to delete a user account

Syntax

userdel -r.

Example

userdelr tom

- this command delete user account as tom

userdel tom

- this command delete user account tom but can notdelete a home directory of tom user.



User configuration files

When a new user account is created, itsentries updates the following system files.

- /etc/passwd

- /etc/group

- /etc/shadow



Creating groups

New group is created by hand-editing the file /etc/group or by using

groupadd command.

Syntax:

groupadd groupname

groupdel command is used to remove the group.

Syntax

groupdel groupname

Groupmod is used to rename the existing groupname.

Syntax:

groupmod n newname oldname



chage commandThe chage command let you specify an expiration limit for a user's

account and password .

Syntax:

chage [option] username

Option

-l lists the current password expiration.

-m set the min. days to change the password.

-M set the max. days to change the password.

-E specific expiration date for user account.

-I set inactive period (in days)-W warning period, number of days before

expiration.



Set userID

It allows an executable file to run under the user or group security

context with the permission of its owner.

SUID can be set as follows:

chmod u+s [filename]

(or)

chmod 4xxx [filename]



Set groupID

Set groupID

Set groupid are also set to directory, any user creating file in that

directory, the file group is directory group name.SGIP can sets as

chmod g+s directory

or

chmod 2xxx directory



Sticky bit

Sticky bit:

Stricky bit is set to the directory, so that only the owner can

delete their own file even the others have write permissions.

Sticky bit can sets as

chmod +t directory

or

chmod 1xxx directory



Switch user

su command is used to switch to another account from the

command line.

This command is most often used by system administrator totemporarily become the root user without logging out of their non-

privileged account.

Syntax

su - [user] -c command



Multi user login

Like unix operating system where multi user login can be done, in

same sense the Linux operating system supports multi user login.

Each user can login in each terminal and can do multi processing

which avoids logging off from the system.

Documents

Session7 Theory