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Every
user who has access to a Linux system
needs a login and a password. Each user must belong to a primary
group and for security or access purposes can belong to several
secondary groups.
In
order to create new logins, modify or delete users, you must already
be logged in as root.
The root login is the highest level and only certain individuals
should have access to the root account.
Options:
- -d
home directory
- -s
starting program (shell)
- -p
password
- -g
(primary group assigned to the users)
- -G
(Other groups the user belongs to)
- -m
(Create the user's home directory
Example:
To add a new user with
- a primary
group of users
- a second
group mgmt
- starting
shell /bin/bash
- password
of xxxx
- home directory
of roger
- create
home directory
- a login
name of roger
useradd
-gusers -Gmgmt -s/bin/shell -pxxxx -d/home/roger -m roger
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Options:
- -d
home directory
- -s
starting program (shell)
- -p
password
- -g
(primary group assigned to the users)
- -G
(Other groups the user belongs to)
Example:
To add the group 'others' to the user roger
usermod
-Gothers roger
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Options:
- -r
(remove home directory)
Example:
To remove the user 'roger' and his home directory
userdel
-r roger
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Options:
- user's
name (Only required if you are
root and want to change another user's password)
Example:
To change the password for the account you are currently logged
in as...
passwd
Enter existing password
Enter new password
Enter new password again (to validate)
Example:
To change the password for the user 'roger' (only you are logged
in as root)...
passwd
roger
Enter existing password (can be either roger's
password or root's password)
Enter new password
Enter new password again
(to validate)
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User
names and primary groups are stored
in /etc/passwd. This file
can be directly edited using the 'vi' editor, although this is
not recommended. Format of the file is...
- User name
(normally all lower case)
- Password
(encrypted - only contains the letter 'x')
- User ID
(a unique number of each user)
- Primary
Group ID
- Comment
(Normally the person's full name)
- Home directory
(normally /home/<user name>
- Default
shell (normally /bin/bash)
Each field
is separated by a colon.
Passwords
for each user are stored in /etc/shadow. This
file should only be changed using the passwd command.
Group
information is stored in /etc/group. This file
can be directly edited using the 'vi' editor. Format of the file
is...
- Group name
- Group password
(hardly ever used)
- Group ID
- User names
(separated by commas)
Each field
is separated by a colon.
Default
files
When a new
user is created, the default files and directories that are created
are stored in /etc/skel.
This directory
can be modified to fit your needs. Modifications
only effect new users and does not change anything for existing
users.
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To switch
to another user, use the su command. This is most commonly
used to switch to the root account.
Example:
To switch to root account...
su
Enter root's passwd
Example:
To switch to the user 'roger'...
su roger
Enter roger's or root's passwd
To return
to original user, enter exit
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