Tuesday, February 21, 2012

SAMBA client in Linux with GUI

We can connect samba server with GUI mode as like windows machine in Linux.

Run Application will be used to access samba server in Linux with GUI.

Alt+F2 used to open Run Application window.

It looks as follows.

run application

Just type smb://{samba server address} and hit Enter.

Ex.

smb://10.1.1.1

This will open your samba share window. Give password if it asks.

Thursday, February 9, 2012

Users and Groups in Linux - 7

gshadow

The gshadow is group password file, It is used for encrypted passwords of group. It is also as like shadow file. It is located at /etc/gshadow.The normal user can's view this and root user only can view and edit.

Location : /etc/gshadow

Fields : 


1 - Group Name : It is name of group.

2 - Encrypted Password : It is current hash of the group's encrypted password.  The encrypted password consists of characters from the 64-character alphabet a thru z, A thru Z, 0 thru 9, \. and /.  If in encrypted password edited with ! or *, the user will not be able to use a unix password to log in.

3 - Administrators : The list of  administrative users separated by comma. This will be done with "gpasswd -A"

4 - Members : The list of members separated by comma.

* Use man pages for more help.

Wednesday, February 8, 2012

Users and Groups in Linux - 6

group

The group file is as like passwd file. passwd is used to store user account information as like group file is used to store group information. It is located at /etc/group. It mainly used for store group name and their user name. Normal user can view this file. But only the root user can edit this.

Location : /etc/group

Fields : 


1 - GroupName : It is name of group.

2 - Password : Normally password is not used in group. It can store encrypted password as like shadow, here it'll be in gshadow. This is useful to implement privileged groups.

3 - GroupId (GID) : It is a unique id for the group. Each user have group id. We can see this at /etc/passwd file.

4 - Group List: This is list of user under this group, means member of this group. Each user separated by comma",".


* Use man pages for more help.

Tuesday, February 7, 2012

Users and Groups in Linux - 5

shadow

The shadow file is mainly used for store Linux User's login passwords as encrypted. It located in /etc/shadow. It's encrypted passwords. So we can't use this passwords straightly for login. The root user only can access this file anything view are edit. Other user don't have permission to view this file.

Location : /etc/shadow

Fields : 
shadow


1 - UserName : It is name of user which we created or superuser or system user.

2 - Encrypted Password : It is current hash of the user's encrypted password.

3 - Last Password Change : It is date of last password changed from 1 Jan 1970. It is UNIX time format (Epoch). You can know more about it here. The encrypted password consists of 13 to 24 characters from the 64 characters alphabet a thru z, A thru Z, 0 thru 9, \. and /. Optionally it can start with a "$" character. This means the encrypted password was generated using another (not DES) algorithm. For example if it starts with "$1$" it means the MD5-based algorithm was used. If in encrypted password edited with ! or *, the user will not be able to use a unix password to log in.

4 - Days until Password change allowed: Till this date the user can change their password.

5 - Days before password change required : After this date the user is forced to change password.

6 - Days warning for password change : How many days want to warn user before the password expire.

7 - Days before account inactive : How many number of days the user can active after password expire .

8 - Days since account expires : The correct day when the login disabled from Jan 1 1970.

9 - Reserved : This is reserved for future use.


* Use man pages for more help.

Monday, February 6, 2012

Users and Groups in Linux - 4

passwd

The passwd file is used for store Linux User account information. And it'll be located in /etc/passwd. It contains root and system user accounts information also. So if any wrong changes happened it affect full Linux system. It only have read permission for all user and have edit permission for root.


Location : /etc/passwd

Fields : 
passwd


1 - UserName : It is name of user which we created or superuser or system user. Here the first "kumar" is user name. Linux allows user name will be 1 to 32 characters.

2 - x : It is location of password file. Here x point out /etc/shadow.

3 - UserID (UID) : It is a unique number for user. It'll be create at the time of user creation. 0 for super user (root). 1 - 500 for system users. 501 to 60000 for normal users and 60001 to 65535 for duplicate user.

4 - GroupID (GID) : It is a unique number for group. It'll be create at the time of user creation. 0 for super user (root). 1 - 500 for system users. 501 to 60000 for normal users and 60001 to 65535 for duplicate user.

5 - User Info : It is normally full name of the user. While create user we can give full name of user. It is generally a short description of the login user. It will be show at login page.   ( Ex. #useradd -c FullName username ).

6 - Home Directory : It is the path of the user directory. Normally files will be saved her when user create a file.

7 - Shell : It is the path of shell for the user. This shell will be used for the specific user.

* Use man pages for more help.

Friday, February 3, 2012

Users and Groups in Linux - 3

How to create user without group ?
Up to i searched and tried, we can't create user without group. We can only create a user with already created group.


How to create user with already created group ?
We can create a user with already created group with "-g" or "-G" option with "useradd" command.
Ex.
   useradd -g group1 user1
     //user1 will be create in group1 and group1 will be primary user of user1
   useradd -G group1 user1
     //user1 will be create in group1 and group1 will be secondary user of user1


How to create user without password ?
We can create a user without password by "passwd" command with "-d" option.
Ex.
   useradd test
   passwsd -d test


How to create user with more groups ?
When we create user, the primary group will be creat at same time or we want to mention group name with "-g" or "-G" option. We can mention multiple groups while create new user. And also we cam mention with "usermod" command for existing user.
Ex.
   useradd -g group1 -G group2,group3 test
     //"group1" is primary group for user "test" ; "group2" and "group3" are secondary groups for user "test".
   usermod -g group1 -G group2,group3 test
     //"group1" is primary group for user "test" ; "group2" and "group3" are secondary groups for user "test".


Is possible to change primary group of user ?
Yes we can change primary group of the user with usermod command.
Ex.
   usermod -g group1 user2


How to remove user from the group ?
We can remove user from the group with "gpasswd" command with "-d" option
Ex.
   gpasswd -d user1 group2
   ** If a user have the group as primary group, we can't remove the user from the group.


How to delete a user ?
We can delete user with "userdel" command, At the time of user creation, if we not mention home directory, it'll create a directory with user-name. We can use "-f" option for delete home directory of the user.
Ex.
   userdel -f user1
     //will delete user as well as user directory.


How to delete a group ?
We can delete a group, if it is not primary group of any user. We can use "groupdel" command for delete a group.
Ex.
   groupdel group1


How to make a user as root privileged ?
It's not recommenced for ever. But we can use sudo for make a user as like root (super user).


Is it possible to edit passwd / group file manually ? And it take affects in user and group ?
We can edit passwd , group files in /etc/. And it'll make changes in user, group and their permissions too.


Is it possible to create a user without user directory and how ?

Yeah we can create user without user(home) directory. The command "useradd" with "-M" will do it. We can login with it in terminal , it'll be as bash. and we can login with it as GUI. In gnome we can do only maintenance work it we know password of administrator/root. And be access some applications.

* Use man pages for more help.

Thursday, February 2, 2012

Users and Groups in Linux - 2

Delete user

userdel command used for delete user. We can do it with root user.

Ex.
#userdel -f username
     // -f for delete user home directory.

Delete group

groupdel command used for delete group. We can use it with root user.


Ex.
#groupdel groupname

Files in Linux for User and Group
  • passwd
  • shadow
  • group
  • gshadow

     passwd
          The passwd file is used for store Linux User account information. And it'll be located in /etc/passwd. It contains root and system user accounts information also. So if any wrong changes happened it affect full Linux system. It only have read permission for all user and have edit permission for root.

     shadow
          The shadow file is mainly used for store Linux User's login passwords as encrypted. It located in /etc/shadow. It's encrypted passwords. So we can't use this passwords straightly for login. The root user only can access this file anything view are edit. Other user don't have permission to view this file.

     group
          The group file is as like passwd file. passwd is used to store user account information as like group file is used to store group information. It is located at /etc/group. It mainly used for store group name and their user name. Normal user can view this file. But only the root user can edit this.

     gshadow
          The gshadow is group password file, It is used for encrypted passwords of group. It is also as like shadow file. It is located at /etc/gshadow.The normal user can's view this and root user only can view and edit.


* Use man pages for more help.

Wednesday, February 1, 2012

Users and Groups in Linux - 1

Users :
Linux is Multi user environment. The users are those who can access the operating system resources with proper permissions as defined already.

Types of users :
I.   System Users
II.  Root User
III. Normal Users

I. System Users - They are default user in linux for some system process and service.
II. Root User - Root user is administrator of Linux System. He have all rights in machine. So should be very carefully with root user. Unknown mistakes may crash the system.
III. Normal Users - They are created by us for some reasons. They are limited users.

Groups : 
Groups are Logical experiences for tying users together. Normally groups are used to share files and permissions.

Types of groups :
I.   System Groups
II.  Root Group
III. Normal Groups

I.   System Groups - They are default groups in linux for some system process and services.
II.  Root Group - Root group is administrator group of Linux System.
III. Normal Groups - They are created by us for some reasons. They are limited groups.

Create User :
Normally we won't and can't create System users, It'll be created by system and or applications for services and maintainable. Root user will be created at the time of Linux installation.
for create a normal user we'll use the command "adduser".
We can use adduser command with root user only.

"useradd" command used to create a user. 
"passwd" command used to create password for user.

Ex.
[[email protected] ~]# useradd user1
[[email protected] ~]# passwd user1
user1

* Typed password won't be shown at terminal window
** Won't ask for password conformation for second time with root. (re enter password)

Create Group :
It also same as user. But When we create a user, the group for the user will be created with same name. A user must be with in a group. Two basic classifications in groups.

i   Primary Group
ii  Secondary Group

Primary Group - The user should be created with this group. He have all rights with in this group.
Secondary Group - The user may or may not have secondary group. And he may or may not have full rights with in this group.

"groupadd" command used to create a group.
Ex.
[[email protected] ~]# groupadd group1

User ID & Group ID
UID stored in /etc/passwd
GID stored in /etc/group

UID and GID are unique number for users and groups.
User and Group ID start with 0 and end with 65535.
0 - root user and group
1 - 500 for system users and groups
501 - 60000 for Normal user and groups
60001 - 65535 for duplicate user and group id.
A user can be assigned with multiple ID and these multiple ID numbers are chosen from this range of Duplicate ID range.

* Use man pages for more help.


While searching about it i got following questions :
i      How to create user without group ?
ii     How to create user with already created group ?
iii    How to create user without password ?
iv    How to create user with more groups ?
v     Is possible to change primary group of user ?
vi    How to remove user from the group ?
vii   How to delete a user ?
viii  How to delete a group ?  
ix    How to make a user as root privileged ?
x     Is it possible to edit passwd / group file manually ? And it take affects in user and group ?
xii   Is it possible to create a user without user directory and how ?