Q1. updates for Set-UID project

There is a modification for the Set-UID project PDF file. It is in
Task 6 (b). We add a "," on the second gcc command. Please use the
latest version via link
http://www.cis.syr.edu/~wedu/Teaching/cis643/Labs/Set-UID/Set-UID.pdf

The following is some information for the students who is not very
familiar with Linux.

1. When you are in the X-window of Ubuntu, you need to run the
"terminal" program to do the project. You can type the commands in the
opened terminal.

2. Use "whoami" to check what is the current user, root or normal user.

3. Use "echo $0" to check the current shell that you are using. Note
that when "root" is running "echo $0", it will return "-su"; when a
normal user runs "echo $0", it will return the name of the shell.

4. the manual page for setuid() system call can be found in
http://linux.die.net/man/3/setuid
For other manual pages for system call like getuid(), you can use
"getuid manual page" in your favorite search engine.

5. A vi tutorial can be found here:
https://engineering.purdue.edu/ECN/Support/KB/Docs/ViTextEditorTutorial

Q2. how to find the directory of a command?

If you don't know where the "passwd" command is, please run the following:

which passwd

Q3. linux command reference

In case you are not familiar with the linux commands, please refer to
http://www.pixelbeat.org/cmdline.html

Q4. How to use gcc to compile c program?
				
The full manual page can be found in
http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/

Simply, if we are only compiling a single program, we can use

# gcc mycode.c

The above command will generate a "a.out" file as the executable
binary. You can run the executable by using the following command:

# ./a.out

Note that, you need to use the current directory information "./" in
front of "a.out". Otherwise, the system may be search the current
directory for you, unless you have specific it in the PATH environment
variable.

If you want to give the filename for the generated executable binary,
you can use

# gcc mycode.c -o myname

Q5. X Server error when booting the system, after I link /bin/sh to /bin/zsh

If you are having the X server error problem when you start the
ubuntu, follow the steps to recover:

1. login as root in the command prompt, password of root is provided
in the manual.pdf

2. execute the following commands (as root user, # is the prompt for
root user, do not enter the "#")

# mount -o remount /
# cd /bin
# rm sh
# ln -s bash sh
# reboot

3. done. The reason why the X server error problem happens is that
something wrong when /bin/sh is linked to /bin/zsh. Therefore, we need
to make /bin/sh link to /bin/bash. However, if we login as a root at
that time, we only have a read-only file system. We need to remount
the whole file system to be able to write. The remaining three steps
is just to build the symbolic link.

4. If you want to avoid the problem, each time before you shutdown
or reboot the system, make sure that /bin/sh is linked to /bin/bash.
Run the following command to see what /bin/sh is linked to

$ ls -la /bin/sh

Q6. 10 seconds session error: your session lasted less than 10 seconds. 
if you have not logged out, this could mean that there is some 
installation problem or that you may be out of diskspace. try logging 
in with one of the failsafe session to see if you can fix this problem.

link: http://pcinfo.thepebkac.net/2009/06/18/linux_error_session_10_seconds.aspx?ref=rss
run as root
# chmod 1777 /tmp