session7 theory
DESCRIPTION
linux ppt 7TRANSCRIPT
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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
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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.
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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.
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5/20/2018 Session7 Theory
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User configuration files
When a new user account is created, itsentries updates the following system files.
- /etc/passwd
- /etc/group
- /etc/shadow
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5/20/2018 Session7 Theory
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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
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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.
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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]
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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
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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
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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
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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.