Page 138 - DCAP106_OPERATING_SYSTEM_TOOLS

Unit 8: Shell Commands

8.1.3 User Account Notes

In Linux, you can access to almost each and every file (configuration files, system, text files
etc.) with no restriction and interruption. You need to be very careful while doing work as
the root (super user). Thus, managing user accounts and groups is an important part of a system
administrator.

Example: An organization XYZ consists of three departments, that is, Marketing,
Technical and Account. Each department have 3–4 employees. The organization demands you to
verify the users of marketing, technical and account departments so that the employees of each
group will be able to view his/her own department file.
Given a situation, if you are familiar with the process of managing these accounts, you can easily
set permissions for the users mentioned above. If not, The commands given below are essential
for the task.

z z useradd : This command is used for creating user account.
This command can be executed by administrators only. On debian, you should use adduser.
For other options like adding expiry date, home directory etc., refer man useradd.

z z passwd : This command is used for changing user password.
If the user has set password before, he/she will be prompted for the first password whereas
superuser is permitted to bypass the step so that forgotten passwords may be changed.

z z usermod : This command is used to modify user account.
z z userdel : This command is used to delete a user account and related files. This command
can be executed by administrators only.

z z groupadd : This command is used to create a new group.
z z groupdel : This command is used delete the group and entries referring to the group.
z z groupmod : This command is used to modify a group definition on the system.
z z chmod : This command is used to modify properties for users.
z z chown : This command is used to change file owner and group.

z z chgrp : This command is used to change group ownership.
8.1.4 Network Commands

Linux is mainly recognized for its use in servers. In 2009, it held a server market share ranging
between 20–40%.
!

Caution It is necessary to know the commands to check the ip address, download files from
the net, get DNS, etc.
Various network commands are discussed below:

z z wget: This command is a non-interactive network downloader.
z z Even if a download fails because of a network problem, it will keep trying again and again
until the complete file has been retrieved. The server will instruct to continue to download
from where it it left off.
z z $ wget url-for-file.

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