Page 217 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Unit 11: User Accounts

You need to use the sudo command which is use to execute a command as another user. It allows notes
a permitted user to execute a command as the superuser or another user, as specified in the /etc/
sudoers (config file that defines or list of who can run what) file. The sudo command allows users
to do tasks on a Linux system as another user.
sudo command

sudo is more more secure than su command. By default it logs sudo usage, command and
arguments in /var/log/secure (Red Hat/Fedora / CentOS Linux) or /var/log/auth.log (Ubuntu
/ Debian Linux).

If the invoking user is root or if the target user is the same as the invoking user, no password
is required. Otherwise, sudo requires that users authenticate themselves with a password by
default. Once a user has been authenticated, a timestamp is updated and the user may then use
sudo without a password for a short period of time (15 minutes unless overridden in sudoers).

/etc/sudoers syntax

Following is general syntax used by /etc/sudoers file:
USER HOSTNAME=COMMAND
Where,

1. USER: Name of normal user
2. HOSTNAME: Where command is allowed to run. It is the hostname of the system where
this rule applies. sudo is designed so you can use one sudoers file on all of your systems.
This space allows you to set per-host rules.
3. COMMAND: A simple filename allows the user to run the command with any arguments
he/she wishes. However, you may also specify command line arguments (including
wildcards). Alternately, you can specify “” to indicate that the command may only be run
without command line arguments.

How do i use sudo?

Give user rokcy access to halt/shutdown command and restart Apache web server. First, Login
as root user. Use visudo command edit the config file:

# visudo
Append the following lines to file:

rokcy localhost=/sbin/halt
rokcy dbserver=/etc/init.d/apache-perl restart
Save and close file . Now rokcy user can restart Apache web server by typing the following
command:

$ sudo /etc/init.d/apache-perl restart
Output:

Password:
Restarting apache-perl 1.3 web server....
The sudo command has logged the attempt to the log file /var/log/secure or /var/log/auth.log file:
# tail -f /var/log/auth.log

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