########## USER, GROUP ADMINISTRATION. ##########
*Unix/Linux is multi user and multi tasking OS.
*Scheme :-
#User always get created with primary group
# One Primary Group per User
*When a user is created in Linux :--
--> home directory ( /home/username)
--> mail account (/var/spool/mail/username)
--> unique UID & GID
*Types of Users.
System Users--> 0 — 499
Normal Users--> 500 — 60,000
User and Group Administration Database Files.
#/etc/passwd
root:x:0:0:root:/root:/bin/bash
u1:x:500:500::/home/u1:/bin/bash
#vim /etc/passwd
u1:x:500:500:prog:/home/u1:/bin/bash
| | | | | | |
1 2 3 4 5 6 7
Discription : -
1. First field : - Login name of the User
2. Second field : - Clear text encrypted password
Note: In case if shadowing is enabled it always denotes a
"x" which means the password is stored in /etc/shadow file
3. Third field : - User id which is unique to every user
4. Fourth field : - Group id which is unique to every group
5. Fifth field : - Comments i.e. user related info like Full Name, Office Add.,Off. No., Home No.
6. Sixth field : - Home directory
7. Seventh field : - Login shell
################################################################
#/etc/shadow
root:$1$d.MWHOEJ$zeLZ2sfTBhNVVWxzpwoAv/:14281:0:99999:7:::
u1:$1$SIOUwX2W$VO/QJmvEp13mlZ9E5B/EP1:14285:0:99999:7:::
#vim /etc/shadow
u1: hjkadfhs8974uyh5jrt/ :13536:0:99999:7: : :
| | | | | | | | |
1 2 3 4 5 6 7 8 9
Discription : -
1. First field : - Login name of the User.
2. Second field : - Clear text encrypted password.
3. Third field : - Number of days since January 1 1970, when the password was last changed.
4. Fourth field : - Minimum number of days gap before a password can be changed again.
5. Fifth field : - Maximum number of days for the validity of a password.
6. Sixth field : - Warning for password expiry to be given before the stipulated number of days.
7. Seventh field : - Number of days after the expiration of password that the account should be disabled.
8. Eight field : - Number of days since 1 January 1970, the account is disabled.
9. Ninth field : - Reserved field.
###############################################################
#/etc/group
root:x:0:root
u1:x:500:
/etc/group
u1:x:500:sachin,tom
| | | |
1 2 3 4
Discription :-
1. Group Name
2. Shadow passwd
3. GID
4. Groupmembers
###################### NEW USERS ###############################
*To create new users.
1)To change UID.
#useradd -u 501 u1
#passwd u1
2)To change primary group.
#useradd -g 501 u2
#passwd u2
*If we change & overwrite the group id so that
should be existed.
3)To overwrite.
#useradd -u 700 -o lax
#usermod -g 700 -o u3
4)To change secondary group.
#useradd -G 700 lax2
#usermod -G 700 lax3
5)To insert the comment.
#useradd -c "pranay" u4
#usermod -c "vijay" u3
6)To change the home directory.
#useradd -d /vikas u4
#usermod -d /vikas u3
7)To change the shell.
#useradd -s /bin/csh u1
#passwd u1
To check.
#tail /etc/passwd
u1:x:561:562::/home/u1:/bin/csh
##################### MODIFY USERS #############################
To modify the existing users by "usermod" command.
1)To modify the user login name.
#usermod -l vikas u1
(N.N) (O.N)
N.N- new name.
O.N- old name.
To check.
# tail /etc/passwd
vikas:x:561:562::/home/u1:/bin/csh
2)To lock the account.
#usermod -L u1
3)To unlock the account.
#usermod -U u1
4)To change the comments.
#usermod -c "laxman" u1
#tail /etc/passwd
u1:x:561:562:laxman:/home/u1:/bin/csh
5)To modify the shell.
#usermod -s /bin/bash u1
#tail /etc/passwd
u1:x:561:562:laxman:/home/u1:/bin/bash
6)To change the UID.
#usermod -u 600 u1
#tail /etc/passwd
u1:x:600:562:laxman:/home/u1:/bin/bash
7)To change the GID with other existing users GID .
#usermod -g 560 u1
#tail /etc/passwd
raj:x:560:560::/home/raj:/bin/bash
u1:x:600:560:laxman:/home/u1:/bin/bash
8)To change the home directory.
#usermod -d /home/u1 u2
#tail /etc/passwd
Before modify the home directory.
u2:x:601:601::/home/u2:/bin/bash
After modify the home directory.
u2:x:601:601::/home/u1:/bin/bash
################### T0 DLETE A USER ##############################
To Delet the user without home directory.
#userdel u1
To Delet the user with home directory.
#userdel -r u1
-r --> recursively.
##################################################################
*To change user setting.
#chage u3
Changing the aging information for u3
Enter the new value, or press ENTER for the default
Minimum Password Age [0]:
Maximum Password Age [99999]:
Last Password Change (YYYY-MM-DD) [2009-02-09]:
Password Expiration Warning [7]:
Password Inactive [-1]:
Account Expiration Date (YYYY-MM-DD) [1969-12-31]:
############### GROUP ADMINISTRATION ########################
1)To create a group.
#groupadd sales
2)To change the GID on new group.
#groupadd -g 700 mkt
3)To check.
#tail /etc/group
sales:x:602:
mkt:x:700:
4)To override.
#groupadd -g 800 -o admin
#tail /etc/group
sales:x:602:
mkt:x:700:
admin:x:800:
*To modify the group.
1)To modify the existing group.
#groupmod -g 610 sales
#tail /etc/group
Before.
sales:x:602:
After.
sales:x:610:
2)To change the groupname.
#groupmod -n marketing mkt
(N.N) (O.N)
#tail /etc/group
Before.
mkt:x:710:
After.
marketing:x:710:
3)To add user into group.
Add single user.
#gpasswd -a u3 admin
Adding user u3 to group admin
Add multyple users.
#gpasswd -M u4,u5 admin
To check.
#tail /etc/group
admin:x:800:u4,u5,u3
To delet a user from group.
#gpasswd -d u3 admin
Removing user u3 from group admin
You have new mail in /var/spool/mail/root
#tail /etc/group
admin:x:800:u4,u5
*To Delet a group.
# groupdel sales
################## END #########################
