Additional Lab Notes

How to become a sudoer

The sudo command allows you to run commmands or applications with root privileges. The syntax is the following:

sudo <command>

For example:

[john@localhost john]$ sudo cat /etc/shadow

The command above prints the shadow file on the screen, showing the encrypted password of every user. Normally, a user does not have permissions to view this file. However, thanks to the sudo command, the user john can view the shadow file. Notice that the first time you use sudo you will be asked to enter your password.

In order to be able to use the sudo command you need to add yourself to the list of sudoers. This is accomplished by editing the file /etc/sudoers as root:

[john@localhost john]$ su
Password: (enter the root password here)
[root@localhost john]# gedit /etc/sudoers

Locate the section User privilege specification, and add the line shown below in bold:

...
# User privilege specification
root       ALL=(ALL)      ALL
john       ALL=(ALL)      ALL
...

where instead of "john" you will type your user name. After saving the file you will be able to use sudo immediately.

Additional GCC options for device drivers

gcc needs special options to compile a device driver. The compiler should be called as following:

gcc -c -nostdinc -I /usr/src/linux-2.4.20/include/ \
    -I /usr/lib/gcc-lib/i386-redhat-linux/3.2/include/ -D MODULE \
    -D __KERNEL__ example.c

Each option is explained below:

• -c: compile only, do not link;
• -nostdinc: do not use the standard include directories;
• -I dir: specifies the include directories;
• -D MODULE and -D __KERNEL__, define the MODULE and __KERNEL__ symbols;