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CMPS 12M
Data Structures Lab
Lab Assignment 1
The purpose of this assignment is threefold: (1) get a basic introduction to the Andrew File System (AFS)
which is the file system used by the ITS unix timshare, (2) learn how to create an executable jar file
containing a Java program, and (3) learn to automate compilation and other tasks using Makefiles.
AFS
Logon to your ITS unix timeshare account at unix.ucsc.edu. If you don't know how to do this, ask for
help at a lab session, or see Lab Assignment 1 from my CMPS 12A/L Spring 2018 webpage:
https://classes.soe.ucsc.edu/cmps012a/Spring18/lab1.pdf
Create a subdirectory within your home directory called cs12b in which you will keep all your work for
both CMPS 12B and CMPS 12M. Create a subdirectory within cs12b called lab1. From within lab1
create a subdirectory called private, then set access permissions on the new directory so that other users
cannot view its contents. Do all this (starting in your home directory) by typing the lines below. The unix
prompt is depicted here as %, although it may look different in your login session. The lines without the
unix prompt are the output of your typed commands.
% mkdir cs12b
% cd cs12b
% mkdir lab1
% cd lab1
% mkdir private
% fs setacl private system:authuser none
% fs listacl private
Access list for private is
Normal rights:
foobar rlidwka
Here foobar will be replaced by your own cruzid. The last line of output says that your access rights to
directory private are rlidwka which means: read, list, insert, delete, write, lock, and administer. In
other words you have all rights in this directory, while other users have none. If you are unfamiliar with
any unix command, you can view its manual page by typing: man <command name>. (Do not type the
angle brackets <>.) For instance man mkdir brings up the man pages for mkdir. Man pages can be very
cryptic, impenetrable even, especially for beginners, but it is best to get used to reading them as soon as
possible. Under AFS, fs denotes a file system command, setacl sets the access control list (ACL) for a
specific user or group of users, and listacl displays the access lists for a given directory. The command
% fs setacl <some directory> <some user> <some subset of rlidwka or all or none>
sets the access rights for a directory and a user. Note that setacl can be abbreviated as sa and listacl
can be abbreviated as la. For instance do la on your home directory:
% fs la ~
Access list for /afs/cats.ucsc.edu/users/a/foobar is
Normal rights:
foobar rlidwka
system:authuser l
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The path /afs/cats.ucsc.edu/users/a/foobar will be replaced by the full path to your home
directory, and your own username in place of foobar. Note that ~ (tilde) always refers to your home
directory, . (dot) always refers to your current working directory (the directory where you are currently
located) and .. (dot, dot) refers to the parent of your current working directory. The group
system:authuser refers to anyone with an account on the ITS unix timeshare. Thus by default, any
user on the system can list the contents of your home directory. No other permissions are set for
system:authuser however, so again by default, no one else can read, insert, delete, write, lock, or
administer your files.
Do fs la ~/cs12b and verify that the access rights are the same for the child directory cs12b as for its
parent, your home directory. Create a subdirectory of private, call it anything you like, and check its
access rights are the same as for its parent. Thus we see that child directories inherit their permissions from
the parent directory when they are created. To get a more comprehensive list of AFS commands do fs
help. For instance you will see that fs lq shows your quota and usage statistics. For more on the
Andrew File System go to
https://en.wikipedia.org/wiki/Andrew_File_System.
Note: Some users may see the group system:anyuser in place of system:authuser when they do the
above commands. This is because newer accounts were created with slightly different ACLs than older
accounts. Whatever the ACL is for ~/cs12b/private, set it so that you have all rights, and other users
have no rights. The distinction between the user groups system:authuser and system:anyuser is of
no significance to us.
Jar Files
Copy the following file to your lab1 directory. (You can find this file in the Examples section of the
class webpage.)
// HelloUser.java
// Prints greeting to stdout, then prints out some environment information.
class HelloUser{
public static void main( String[] args ){
String userName = System.getProperty("user.name");
String os = System.getProperty("os.name");
String osVer = System.getProperty("os.version");
String jre = System.getProperty("java.runtime.name");
String jreVer = System.getProperty("java.runtime.version");
String jvm = System.getProperty("java.vm.name");
String jvmVer = System.getProperty("java.vm.version");
String javaHome = System.getProperty("java.home");
long freemem = Runtime.getRuntime().freeMemory();
long time = System.currentTimeMillis();
System.out.println("Hello "+userName);
System.out.println("Operating system: "+os+" "+osVer);
System.out.println("Runtime environment: "+jre+" "+jreVer);
System.out.println("Virtual machine: "+jvm+" "+jvmVer);
System.out.println("Java home directory: "+javaHome);
System.out.println("Free memory: "+freemem+" bytes");
System.out.printf("Time: %tc.%n", time);
}
}
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You can compile this in the normal way by doing javac HelloUser.java then run it by doing the
command java HelloUser. Java provides a utility called jar for creating compressed archives of
executable .class files. This utility can also be used to create an executable jar file that can then be
run by just typing its name at the unix prompt (with no need to type java first). To do this you must first
create a manifest file that specifies the entry point for program execution, i.e. which .class file contains
the main() method to be executed. Create a text file called Manifest containing just one line:
Main-class: HelloUser
If you don’t feel like opening up an editor to do this you can just type
% echo Main-class: HelloUser > Manifest
The unix command echo prints text to stdout, and > redirects the output to a file. Now do
% jar cvfm HelloUser Manifest HelloUser.class
The first group of characters after jar are options. (c: create a jar file, v: verbose output, f: second argument
gives the name of the jar file to be created, m: third argument is a manifest file.) Consult the man pages to
see other options to jar. The second argument HelloUser is the name of the executable jar file to be
created. The name of this file can be anything you like, i.e. it does not have to be the same as the name of
the .class file containing function main(). For that matter, the manifest file need not be called
Manifest, but this is the convention. Following the manifest file is the list of .class files to be archived.
In our example this list consists of just one file: HelloUser.class. At this point we would like to run
the executable jar file HelloUser by just typing its name, but there is one problem. This file is not
recognized by Unix as being executable. To remedy this do
%chmod +x HelloUser
As usual, consult the man pages to understand what chmod does. Now type HelloUser to run the program.
The whole process can be accomplished by typing five lines:
% javac –Xlint HelloUser.java
% echo Main-class: HelloUser > Manifest
% jar cvfm HelloUser Manifest HelloUser.class
% rm Manifest
% chmod +x HelloUser
Notice we have removed the now unneeded manifest file. Note also that the –Xlint option to javac enables
recommended warnings. The only problem with the above procedure is that it’s a big hassle to type all
those lines. Fortunately there is a unix utility that can automate this and other processes.
Makefiles
Large programs are often distributed throughout many files that depend on each other in complex ways.
Whenever one file changes all the files depending on it must be recompiled. When working on such a
program it can be difficult and tedious to keep track of all the dependencies. The Unix make utility
automates this process. The command make looks at dependency lines in a file named Makefile. The
dependency lines specify relationships between source files by indicating a target file that depends on one
or more prerequisite files. If a prerequisite has been modified more recently than its target, make updates
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the target file based on construction commands that follow the dependency line. make will normally stop
if it encounters an error during the construction process. Each dependency line has the following format.
target: prerequisite-list
construction-commands
The dependency line is composed of the target and the prerequisite-list separated by a colon. The
construction-commands may consist of more than one line, but each line must start with a tab
character.
Start an editor and copy the following lines into a file called Makefile.
#------------------------------------------------------------------------------
# A simple Makefile
#------------------------------------------------------------------------------
HelloUser: HelloUser.class
echo Main-class: HelloUser > Manifest
jar cvfm HelloUser Manifest HelloUser.class
rm Manifest
chmod +x HelloUser
HelloUser.class: HelloUser.java
javac -Xlint HelloUser.java
clean:
rm -f HelloUser HelloUser.class
submit: README Makefile HelloUser.java
submit cmps012b-pt.w19 lab1 README Makefile HelloUser.java
Anything following # on a line is a comment and is ignored by make. The second line says that the target
HelloUser depends on HelloUser.class. If HelloUser.class exists and is up to date, then
HelloUser can be created by doing the construction commands that follow. Remember that all indentation
is accomplished via the tab character. The next target is HelloUser.class which depends on
HelloUser.java. The next target clean is what is sometimes called a phony target since it doesn’t
depend on anything and just runs a command. Likewise the target submit does not compile anything, but
does have some dependencies. Any target can be built (or executed if it is a phony target) by doing make
<target name>. Just typing make creates the first target listed in the Makefile. Try this by doing make
clean to get rid of all your previously compiled stuff, then do make again to see it all created again.
Your output from make should look something like:
% make
javac -Xlint HelloUser.java
echo Main-class: HelloUser > Manifest
jar cvfm HelloUser Manifest HelloUser.class
added manifest
adding: HelloUser.class(in = 1577) (out= 843)(deflated 46%)
rm Manifest
chmod +x HelloUser
The make utility allows you to create and use macros within a Makefile. The format of a macro definition
is ID = list where ID is the name of the macro (by convention all caps) and list is a space separated
list of filenames. Then the expression $(list) below the definition in the Makefile, refers to this list of
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files. Move your existing Makefile to a temporary file, then start your editor and copy the following lines
to a new file, again called Makefile.
#------------------------------------------------------------------------------
# Another Makefile with macros
#------------------------------------------------------------------------------
JAVASRC = HelloUser.java
SOURCES = README Makefile $(JAVASRC)
MAINCLASS = HelloUser
CLASSES = HelloUser.class
JARFILE = HelloUser
SUBMIT = submit cmps012b-pt.w19 lab1
all: $(JARFILE)
$(JARFILE): $(CLASSES)
echo Main-class: $(MAINCLASS) > Manifest
jar cvfm $(JARFILE) Manifest $(CLASSES)
rm Manifest
chmod +x $(JARFILE)
$(CLASSES): $(JAVASRC)
javac -Xlint $(JAVASRC)
clean:
rm $(CLASSES) $(JARFILE)
submit: $(SOURCES)
$(SUBMIT) $(SOURCES)
Notice that the definition of a macro can contain other macros in its right hand side, as in the list SOURCES
above. Run this new Makefile and observe that it is equivalent to the previous one. The macros define text
substitutions that happen before make interprets the file. Study this new Makefile until you understand
exactly what substitutions are taking place. Now create your own Hello program and call it
HelloUser2.java. It can say anything you like, but just have it say something different from the original.
Add HelloUser2.java to the JAVASRC list, add HelloUser2.class to the CLASSES list and change
MAINCLASS to HelloUser2. Also change the macro JARFILE to just Hello (emphasizing that the jar
file can have any name.) Remember that all indentation in a Makefile must be accomplished with the tab
character, not spaces, or the make utility will not work.
#------------------------------------------------------------------------------
# Yet another Makefile with macros
#------------------------------------------------------------------------------
JAVASRC = HelloUser.java HelloUser2.java
SOURCES = README Makefile $(JAVASRC)
MAINCLASS = HelloUser2
CLASSES = HelloUser.class HelloUser2.class
JARFILE = Hello
SUBMIT = submit cmps012b-pt.w19 lab1
all: $(JARFILE)
$(JARFILE): $(CLASSES)
echo Main-class: $(MAINCLASS) > Manifest
jar cvfm $(JARFILE) Manifest $(CLASSES)
rm Manifest
chmod +x $(JARFILE)
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$(CLASSES): $(JAVASRC)
javac -Xlint $(JAVASRC)
clean:
rm $(CLASSES) $(JARFILE)
submit: $(SOURCES)
$(SUBMIT) $(SOURCES)
This new Makefile compiles both HelloUser classes (even though neither one depends on the other.) Notice
however the entry point for program execution has been changed to function main() in your program
HelloUser2.java. Macros make it easy to make changes like this, so learn to use them. To learn more
about Makefiles follow the links posted on the class webpage.
We've discussed three Makefiles in this project. If you rename them Makefile1, Makefile2 and
Makefile3 respectively (since you can't have three files with the same name), you'll find that the make
command does not work since a file called Makefile no longer exists. Instead of renaming files to run
the Makefile you want, you can use the -f option to the make command, and specify the name of your
Makefile. For instance
% make -f Makefile2
runs Makefile2. If you want to specify something other than the first target, place it after the file name
on the command line. For instance
% make –f Makefile3 clean
runs the clean target in Makefile3.
What to turn in
All files you turn in for this and other assignments (in both 12B and 12M) should begin with a comment
block giving your name, cruzid, class (12B or 12M), date, a short description of its role in the project, the
file name and any special instructions for compiling and/or running it. Create one more file called
README which is just a table of contents for the assignment. In general README lists all the files being
submitted (including README) along with any special notes to the grader. Use what you've learned in
this project to write a Makefile that creates and archives both .class files (HelloUser.class and
HelloUser2.class) in an executable jar file called Hello, and that runs function main() from
HelloUser2.class. It should also include clean and submit utilities, as in the above examples. Also
add a check utility that checks that the project was properly submitted.
See the webpage for instructions on using the submit command and for checking that a project was
properly submitted. Submit the following files to the assignment name lab1:
README described above
Makefile described above
HelloUser.java unchanged from above
HelloUser2.java described above
You can either type the submit command directly:
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% submit cmps012b-pt.w19 lab1 README Makefile HelloUser.java HelloUser2.java
or use the Makefile itself:
% make submit
This is not a difficult assignment, especially if you took CMPS 12A from me (see lab4 from the Spring
2018 offering of that class), but start early and ask questions if anything is unclear.