Files in the /bin directory can be run without elevated privileges. For example, the pwd (present working directory) command is in the /bin directory (/bin/pwd). Any user will be able to execute the pwd command, because the pwd command does not require elevated privileges.
[Tim@server1 ~]# pwd /home/Tim
[Tim@server1 ~]# ifdown eth0 Permission denied
The /etc/sudoers file is what is used to determine if a user has permission to run commands that require elevated privileges. The /etc/sudoers file should not be edited using your preferred editor, such as vi or nano, because improperly editing the /etc/sudoers file can remove the ability to run commands that require elevated privileges. The visudo command should be used to edit the /etc/sudoers file. Only root can execute the visudo command.
The syntax of lines in the /etc/sudoers file is users hosts=(user:group) commands. By default, there should be a line that allows root to run all commands that require elevated privileges. Do not comment out this line.
root ALL=(ALL:ALL) ALL
Sometimes, the line will only have (ALL) instead of (ALL:ALL). This means that ALL is only applied to user, and not to group.
root ALL=(ALL) ALL
Refer to these articles for the steps on how to give a user or group permission to run certain commands.
Now, the user or group that has been granted permission to run certain commands can use the sudo command to issue commands that require elevated privileges.
Recall that the syntax of lines in the /etc/sudoers file is users hosts=(user:group) commands. Aliases can be used for each section. Let's take an example where multiple users need permission to run multiple commands on certain hosts using a certain user and group. For example, Tim and Tammy and Roger and Dawn need permission to execute the halt and init and poweroff and reboot and shutdown and telinit commands on 192.168.0.6 as admins.
Tim,Tammy,Roger,Dawn 192.168.0.6=(admins)/sbin/halt, /sbin/init, /sbin/poweroff, /sbin/reboot, /sbin/shutdown, /sbin/telinit
Aliases can be used. Instead of listing Tim, Tammy, Roger, Dawn, a User_Alias can be created.
User_Alias REBOOT_USERS = Tim, Tammy, Roger, Dawn
Instead of listing halt and init and poweroff and reboot and shutdown and telinit, a Cmnd_Alias can be created.
Cmnd_Alias REBOOT_COMMANDS = /sbin/halt, /sbin/init, /sbin/poweroff, /sbin/reboot, /sbin/shutdown, /sbin/telinit
Instead of listing 192.168.0.6, a Host_Alias can be created.
Host_Alias REBOOT_HOSTS = 192.168.0.6
Instead of listing root:admins, a Runas_Alias can be created..
Runas_Alias REBOOT_RUNAS = admins
The aliases can then be used.