Laboratory 1 – UNIX Tools and Development Environment

Learning Outcomes

After this laboratory, the student should be able to:

log in to the AGH UNIX server,
configure the shell environment to use English,
configure nano and indent,
use basic UNIX commands and manual pages,
create, format, compile and run a simple C program,
explain the stages of compilation: preprocessing, assembly, object code and linking,
explain the difference between a header file and a library,
recognize simple examples of undefined behaviour.

Task 1 — Log in to the AGH student server

Use SSH to connect to the AGH UNIX server.

ssh your_login@student.agh.edu.pl

Detailed instructions (if you have never connected before)

Before connecting to the server, make sure that your UNIX account is activated.

Go to the AGH network services panel:

https://panel.agh.edu.pl

After logging in:

Open UNIX accounts
Activate the account on student.agh.edu.pl

Then connect to the server using SSH:

ssh your_login@student.agh.edu.pl

If you connect for the first time, the system may ask you to confirm the host key.

yes

Task 2 — Configure the terminal environment to use English

After logging in, configure the shell so that terminal tools display messages in English.

Step 1 — Open the profile file

LANG=en nano ~/.profile

The prefix LANG=en forces nano to start in English.

Step 2 — Add locale settings

export LC_ALL=C.UTF-8
export LC_CTYPE=C.UTF-8
export LANG=C.UTF-8
export LC_COLLATE=C.UTF-8
export LANGUAGE=en
export LC_MESSAGES=C.UTF-8

Step 3 — Save the file and exit nano

Press:

Ctrl + X

Then press:

Y

and confirm the filename with:

Enter

Step 4 — Log out and reconnect

exit

Step 5 — Verify the configuration

locale

You should see values similar to:

LANG=C.UTF-8
LANGUAGE=en
LC_MESSAGES=C.UTF-8
LC_ALL=C.UTF-8

If nano still opens in another language, you can always force English with:

LANG=en nano filename

Task 3 — Configure development tools

Prepare the editor and formatter used in the course.

Step 1 — Configure nano

nano ~/.nanorc

Add:

set linenumbers
set autoindent
set tabsize 4
set tabstospaces

Step 2 — Configure indent

nano ~/.indent.pro

Add:

-kr
-brf
-i4
-ci4
-cli4
-l120
-nut
-npcs
-npsl
-bad
-bap

option	effect
`-kr`	K&R style for braces and control statements
`-brf`	keep the opening brace of a function definition on the same line
`-i4`	basic indentation = 4 spaces
`-ci4`	continuation indentation = 4 spaces
`-cli4`	case label indentation = 4 spaces
`-l120`	maximum line length = 120
`-nut`	use spaces instead of tabs
`-npcs`	do not put a space between a function name and `(`
`-npsl`	keep the selected style for function declaration formatting
`-bad`	blank line after declarations
`-bap`	blank line after function definitions

Task 4 — Manual pages and basic UNIX commands

Learn how to use documentation and navigate the file system.

Step 1 — Learn how to use `man`

man man

key	action
`Space`	next page
`Enter`	next line
`b`	previous page
`/text`	search text
`n`	next search result
`q`	quit

Step 2 — Explore documentation of basic commands

man mkdir
man pwd
man ls
man cat
help cd

Step 3 — Directory navigation exercise

pwd
cd ~
ls
mkdir I2PL
ls
cd I2PL
pwd
mkdir lab1
ls
cd lab1
pwd
cd
ls
cd I2PL/lab1
ls

Step 4 — Create a simple directory structure

Create the following directory structure:

I2PL
└── lab1

Verify it using:

ls
cd ..
ls
cd lab1
ls

The tree command may not be available on the server. If it is installed, you can also use:

tree

Otherwise, a recursive listing such as:

ls -R

may also help you inspect the directory structure.

Task 5 — Create the first C program

Create a simple program that prints text on the screen.

nano hello.c

#include <stdio.h>

int main(void) {
    printf("Hello\n");
    return 0;
}

Task 6 — Format the source code

Use indent to format the program according to the course style.

indent hello.c

The indent tool automatically reformats C code according to the selected style.

Compare the formatted file with the backup copy:

diff hello.c hello.c~

Task 7 — Compile and run the program

Compile the program and execute it from the current directory.

Step 1 — Compile

gcc -Wall hello.c -o hello

Step 2 — Run

./hello

Task 8 — Explore the compilation pipeline

Examine the stages performed by the compiler.

Step 1 — Preprocessing

gcc -E hello.c > hello.i
wc -l hello.i

Step 2 — Assembly generation

gcc -S hello.c

Step 3 — Object file

gcc -c hello.c

This creates:

hello.o

Step 4 — Full compilation and linking

gcc hello.c -o hello

command	stage	output
`gcc -E`	preprocessing	`.i`
`gcc -S`	assembly generation	`.s`
`gcc -c`	object file generation	`.o`
`gcc`	full compilation + linking	executable file

Task 9 — Header file vs library

Understand the difference between declarations and implementations.

Step 1 — Locate the header file

whereis stdio.h

Step 2 — Check linked libraries

ldd hello

Step 3 — Find printf in the C library

nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep " printf@"

element	role
`stdio.h`	header file with declarations
`libc.so.6`	library with implementations
`printf`	function declared in the header and implemented in the library

A header file tells the compiler what exists. A library provides the actual code.

Task 10 — Variables and formatted output

Try formatted output with integers and floating-point values.

#include <stdio.h>

int main(void) {
    int x = 1;
    int y;

    printf("x=%d, y=%d\n", x, y);
    printf("x=%5d, y=%5d\n", x, y);

    float f1 = 12.0f;
    float f2 = 12.3678f;

    printf("f1=%f, f2=%f\n", f1, f2);
    printf("f1=%8.2f, f2=%8.2f\n", f1, f2);

    return 0;
}

Compile and run the program several times. Observe that y may have a different value each time.

Task 11 — Undefined behaviour

See what happens when the format specifier does not match the argument type.

#include <stdio.h>

int main(void) {
    printf("%d\n", 3.14);
    return 0;
}

Step 1 — Compile normally

gcc test2.c -o test2

Step 2 — Run several times

./test2

Step 3 — Compile with warnings

gcc -Wall test2.c -o test2

The format specifier %d expects int, but 3.14 is a double. This is an example of undefined behaviour.

Task 12 — Running programs and PATH

Understand why programs in the current directory are executed with ./program.

Step 1 — Try running without `./`

test2

You should see:

command not found

Step 2 — Run correctly

./test2

Step 3 — Check PATH

echo $PATH

In Linux the current directory is usually not included in PATH. That is why programs in the current directory are run with ./program.

What will be checked during the next laboratory

The student should be able to:

log in to the server,
configure the shell environment and development tools,
use manual pages and basic UNIX commands,
create, format, compile and run a simple C program,
explain the meaning of gcc -E, gcc -S, gcc -c and gcc,
explain the difference between a header file and a library,
recognize simple examples of undefined behaviour.

Quick Summary

Server: student.agh.edu.pl
Editor: nano
Formatter: indent
Compiler: gcc
Manual pages: man
Run program: ./program

Recommended Code Style

#include <stdio.h>

int main(void) {
    printf("Hello\n");
    return 0;
}

Important Concepts

stdio.h is a header file, not a library
libc.so.6 contains implementations such as printf
always compile with -Wall
local variables are not automatically initialized
printf format specifiers must match argument types

Recommended Commands

man gcc
man mkdir
help cd
gcc -E hello.c
gcc -S hello.c
gcc -c hello.c
ldd hello
nm hello.o
objdump -d hello | grep -A15 "<main>"