Summary

Security is a central concern of the system administrator. In this chapter, you have learned the basic concepts and practices of system security. The tools introduced will be useful when attempting to secure a system connected to the Internet.

Questions

1.	Which of the following files do not need to be owned by a user ? Directories Device files Metadevices None of the above
2.	Which of the following printouts represents a possible output from the id command? gid=1001(scott) uid=100(tiger) uid=1001(scott) gid=100(tiger) uid=1001(scott) gid=-100(tiger) None of the above
3.	What is the UID of the superuser? 1 100 666
4.	Name one restriction placed on the root account? The root user cannot read other users e-mail The root user cannot delete a user s account without their permission The root user cannot rlogin to another system as root without a credential The root user cannot modify disk partition sizes
5.	Name the default permissions mask set in the user s shell? mask omask chmod umask
6.	How could read, write, and execute permissions be set on a file called /etc/passwd for all users? chmod a+rwx /etc/passwd chmod o+rwx /etc/passwd chmod u+rwx /etc/passwd chmod u-rwx /etc/passwd
7.	How could read, write, and execute permissions be removed from a file called /etc/passwd for all users who do not belong to the owner s group ? chmod a+rwx /etc/passwd chmod o+rwx /etc/passwd chmod u+rwx /etc/passwd chmod o-rwx /etc/passwd
8.	Which command displays the username, connecting line, date of login, idle time, process ID, and a comment for all logged-in users? who w which show

Answers

1.	D. All files need to be owned by someone.
2.	B. All UIDs and GIDs must be positive and the UID precedes the GID.
3.	A. The UID of the superuser is always 0, even if the name is changed from root to something else.
4.	C. Credentials are required, unless blanket access is granted by use of hosts .equiv or .rhosts.
5.	D. The umask is the default permissions mask.
6.	A. All users are denoted by a in permissions strings.
7.	D. Permissions are removed with - .
8.	A. The who command displays the username, connecting line, date of login, idle time, process ID, and a comment for all logged-in users.