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Project 1 2022
The goal of this project is to develop a system utility program,
named estimatecron,
which checks the correctness of a simplified crontab-file,
and determines some simple metrics about the set of commands specified in the file.
Successful completion of the project will enhance your understanding of
core features of the C11 programming language,
functions from the C11 standard library, and
your operating system's system-calls; and
familiarise yourself with online systems' documentation.
Introduction
Most Unix-based systems,
such as Linux and macOS,
employ a command named cron
which supports the scheduling and execution of non-interactive,
often long-running, commands.
The cron process 'wakes-up' every minute,
reads from a text file termed a crontab-file,
and commences the execution of any commands that should run at that time.
cron is often used to schedule backups at times when a machine will otherwise
be idle,
and to support a list of task requests, a batch queue,
on supercomputer and cloud-computing platforms.
(Do not go into too much depth,
but you can read about the standard cron command from
section 8 of your system's online manual,
and read about the standard crontab format from
section 5 of your system's online manual.)
For this project we will use the information in two text files,
termed the crontab-file and the estimates-file,
to anticipate the required computing load on a system,
based on the execution time of previously executed commands.
A typical invocation of your project will be:
prompt> ./estimatecron month crontab-file estimates-file
which specifies the month (of the current year)
to be analysed (either an integer 0..11, or a 3-character name),
and the name of the two required text files
(you may choose any names for the files).
Your estimatecron program should
check the validity of the information in its input files (reporting any errors),
simulate (better word?) the execution of commands invoked during the requested month,
and report the values of:
the name of the most frequently executed command (a single word),
the total number of commands invoked (a non-negative integer),
and
the maximum number of commands running at any time (a non-negative integer).
File formats
Your estimatecron program should read information from 2 text files -
a simplified crontab-file which specifies at which times commands should be executed,
and an estimates-file which specifies the average execution times (in minutes) of commands.
The crontab-file consists of 2 types of lines:
-
comment lines are lines whose first non-whitespace (space ' ', or tab '\t') character
is a '#' (the hash character).
They are used to document the file or to 'comment out' other unwanted lines.
Their contents is ignored.
- command lines consist of at least 6 'words' separated by
one-or-more whitespace characters.
The first 5 words contain, in order,
the minute (0..59),
the hour (0..23),
the day of the month (1..31),
the month (0..11),
and
the day of the week (0=sun...6=sat)
when a command should be invoked.
As a special case,
any of the first 5 words may be just a '*' (an asterisk),
indicating that all possible (valid) values are being specified.
The words for
the month
and
the day of the week,
may be 3-letter lowercase abbreviations of their possible values,
such as
jan,
feb,
mar...
and
sun,
mon,
tue...
The 6th word provides the name of the command to be executed.
A representative crontab-file may include the lines:
# execute a command at 3AM every day
0 3 * * * daily-backup
#
# execute a command at 4:15AM every Sunday
15 4 * * sun weekly-backup
#
# start thinking about the project....
0 10 22 7 mon deep-thought
#
# submit my project automatically, just in case I forget!
59 16 16 8 * submit-project
#
# mail out a monthly newsletter
0 2 1 * * send-monthly-newsletter
The estimates-file consists of 2 types of lines:
Project requirements and fine-print
- The project may be completed individually or in teams of two
(but not teams of three).
The choice of project partners is up to you -
you will not be automatically assigned a project partner.
- Your project should be written in the C11 programming language,
in a single source-code file named estimatecron.c
- The crontab-file and the estimates-file
will each contain at most 20 non-comment lines.
Each line will be at most 100 characters long,
and each command name will be at most 40 characters long.
- Your project should check for data errors in both the
crontab-file and the estimates-file.
If any errors are found,
only the first error should be reported and the program should terminate.
- Every command name appearing in the crontab-file
will be also appear in the estimates-file.
- Your project should simulate (better word?) the execution of the commands
specified in the crontab-file,
for the month specified on the command-line.
There is no need to consider leap-years (or leap seconds!).
- At most 20 processes will ever be executing at the same time
(during the same minute),
and multiple instances of the same command may run at the same time.
- Your project only needs to simulate the execution of processes
for the requested month (of the current year).
All processes will have terminated before the end of the requested month.
- Your project should not attempt to execute any of the commands
in the crontab-file
(using, for example, fork() and exec()).
- Your submitted project may produce any output you wish,
typically debug output.
It does not need to describe what it is during.
Only the very last line will be considered during (automated) marking.
It must provide 3 words separated by one-or-more whitespace characters:
- the name of the most frequently executed command (a single word),
- the total number of commands invoked (a non-negative integer), and
- the maximum number of commands running at any time (a non-negative integer).
- A command whose estimated running time is, say, 1 minute,
will have terminated before new commands are considered at the beginning
of the next minute (imagine they run for at most 59 seconds).
- The project can be successfully completed without using any
dynamic memory allocation in C (such as with malloc()).
You may choose to use dynamic memory allocation,
but will not receive additional marks for doing so.
- Your project should not depend upon any libraries
(such as 3rd-party downloaded from the internet)
other than your system's standard library
(providing OS, C, and POSIX functions).
Assessment
The project is due
5:00pm Friday 16th September (end of week 7).
and is worth 25% of your final mark for CITS2002.
It will be marked out of 50.
- 25 of the possible 50 marks will come from the correctness of your solution
(automated marking).
Correctness includes checking the validity of input data,
and reporting the correct final results.
- 25 of the possible 50 marks will come from assessing your programming style,
including your use of meaningful comments;
well chosen identifier names;
appropriate choice of basic data-structures, data-types and functions;
and
appropriate choice of control-flow constructs (manual marking).
During the marking, attention will
obviously be given to the correctness of your solution. However, a correct
and efficient solution should not be considered as the perfect, nor
necessarily desirable, form of solution. Preference will be given to well
presented, well documented solutions that use the appropriate features of
the language to complete tasks in an easy to understand and easy to follow
manner. That is, do not expect to receive full marks for your project simply
because it works correctly. Remember, a computer program should not only
convey a message to the computer, but also to other human programmers.
Good luck!
Chris McDonald.
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