User Administration in Linux
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This document discusses user administration in Linux. It describes the different types of user accounts - root, system, and user accounts. The root account has complete control while system accounts are for specific system functions. User accounts provide interactive access for general users. Groups are used to logically group user accounts. The main user administration files are /etc/passwd, /etc/shadow, /etc/group, and /etc/gshadow. Basic commands for managing users include useradd, usermod, userdel, groupadd, groupmod, and groupdel. Creating, modifying, and deleting users and groups are demonstrated.
![CREATE A GROUP
groupadd [-g gid [-o]] [-r] [-f] groupname --OR-- groupadd local_admin
1 -g GID - - The numerical value of the group's ID
2 -o -- This option permits to add group with non-unique GID
3 -r -- This flag instructs groupadd to add a system account
4 -f -- This option causes to just exit with success status
5 groupname --- Actual group name to be created
$ groupadd developers](https://image.slidesharecdn.com/linux-useradministration-190204094413/85/User-Administration-in-Linux-8-320.jpg)
User Administration in Linux
- 2. Introduction In this section, I will discuss in detail about user administration in Linux. There are three main types of user accounts on a Linux Server: Root, System and User Accounts
- 3. ROOT ACCOUNT This is also called superuser and would have complete control of the Linux system. A superuser can run any commands without any restriction. This user should therefore not be used to access the system directly, it should be assumed as a system administrator.
- 4. SYSTEM ACCOUNTS •System accounts are those needed for the operation of system-specific components, for example mail accounts and the sshd accounts. These accounts are usually needed for some specific function on your Linux system, and any modifications to them could adversely affect the system.
- 5. USER ACCOUNTS User accounts provide interactive access to the system for users and groups. General users are typically assigned to these accounts and usually have limited access to critical system files and directories. Linux uses Group Account which logically groups a number of accounts. Every account would be a part of another group account. A group plays important role in handling file permissions and process management.
- 6. MANAGING USERS AND GROUPS IN LINUX There are four main user administration files − 1. /etc/passwd − Keeps the user account and password information. This file holds the majority of information about accounts on the Unix system. 2. /etc/shadow − Holds the encrypted password of the corresponding account. Not all the systems support this file. 3. /etc/group − This file contains the group information for each account. 4. /etc/gshadow − This file contains secure group account information.
- 7. BASIC USER ADMINISTRATION COMMANDS 1 Useradd: - Adds accounts to the system 2 Usermod: - Modifies account attributes 3 Userdel: - Deletes accounts from the system 4 Groupadd: - Adds groups to the system 5 Groupmod: - Modifies group attributes 6 Groupdel: - Removes groups from the system
- 8. CREATE A GROUP groupadd [-g gid [-o]] [-r] [-f] groupname --OR-- groupadd local_admin 1 -g GID - - The numerical value of the group's ID 2 -o -- This option permits to add group with non-unique GID 3 -r -- This flag instructs groupadd to add a system account 4 -f -- This option causes to just exit with success status 5 groupname --- Actual group name to be created $ groupadd developers
- 9. MODIFY A GROUP To modify a group, use the groupmod syntax − $ groupmod -n new_group_name old_group_name $ groupmod -n sysadmin local_admin $ groupmod -g 484 sysadmin
- 10. DELETE A GROUP We will quickly look at how to delete a group. To delete an existing group, all you need is the groupdel command and the group name, e.g: $ groupdel local_admin This removes only the group, not the files associated with that group. The files are still accessible by their owners.
- 11. CREATE AN ACCOUNT 1 -d homedir Specifies home directory for the account 2 -g groupname Specifies a group account for this account 3 -m Creates the home directory if it doesn't exist 4 -s shell Specifies the default shell for this account 5 -u userid You can specify a user id for this account 6 accountname Actual account name to be created useradd -d homedir -g groupname -m -s shell -u userid accountname
- 12. If you do not specify any parameter, then the system makes use of the default values. The useradd command modifies the /etc/passwd, /etc/shadow, and /etc/group files and creates a home directory. This is the example that creates an account samojo, setting its home directory to /home/samojo and the group as sysadmin. This user would have Korn Shell assigned to it $ useradd -d /home/samojo -g sysadmin -s /bin/ksh samojo Before issuing the above command, make sure you already have the sysadmin group created using the groupadd command. Once an account is created you can set its password using the passwd command. E.g passwd samojo
- 13. MODIFY AN ACCOUNT The usermod command enables you to make changes to an existing account from the command line. It uses the same arguments as the useradd command, plus the -l argument, which allows you to change the account name. Eg, to change the account name samojo to samojo00 and to change home directory accordingly $ usermod -d /home/samojo00 -m -l samojo samojo00
- 14. DELETE AN ACCOUNT The userdel command can be used to delete an existing user. This is a very dangerous command if not used with caution. There is only one argument or option available for the command .r, for removing the account's home directory and mail file. Eg, to remove account samojo00, type the command: $ userdel -r samojo00 If you want to keep the home directory for backup purposes, omit the -r option. You can remove the home directory as needed at a later time
Editor's Notes
- #7: Check all the above files using the cat command.
- #8: You can use Manpage Help to check complete syntax for each command mentioned here.
- #9: If you do not specify any parameter, then the system makes use of the default values. Following example creates a local_admin group with default values, which is very much acceptable for most of the administrators.
- #13: When you type passwd accountname, it gives you an option to change the password, provided you are a superuser. Otherwise, you can change just your password using the same command but without specifying your account name.