Student Details

Field	Value
Name	‎أحمد علي أحمد علي عثمان
Code	20240592
Section	1
Number	15

Linux Essentials Assignment 2

Task No.01

1.1 Explain types of processes in linux and how you can display all currently running processes in full format on a system.

Types of Processes in Linux

1. Parent process
   A parent process is any process that creates another process using system calls such as fork() or clone(). Every process in Linux has a parent process, except for the very first process started by the kernel. If a process is launched from a terminal, its parent is typically the shell (e.g., bash, sh), not the kernel directly.
2. Child process
   A child process is a process created by another process (its parent). The child inherits certain attributes from its parent (such as environment variables and file descriptors) but has a unique process ID (PID). Each child process always has exactly one parent at any given time.
3. Orphan process
   An orphan process occurs when a parent process terminates before its child finishes execution. When this happens, the orphaned child is automatically re-parented to the system's init process (systemd on modern Linux systems, historically init). The orphan's PPID becomes the PID of systemd usually PID 1 or PID 0.
4. Zombie process
   A zombie process is a process that has completed execution but still has an entry in the process table because its parent has not yet collected its exit status using wait() or waitpid(). Zombie processes consume no CPU and minimal memory, but they remain visible in process listings until reaped by their parent.
5. Daemon process
   A daemon process is a long-running background process that typically starts during system boot or on demand and does not interact directly with a terminal. Daemons are usually detached from any controlling TTY, which is why their TTY field often appears as ? in process listings. Examples include sshd, cron, and systemd services.

Displaying All Running Processes in Full Format

To display all currently running processes in full format, use:

ps -ef

• -e : show all processes
• -f : full-format listing (UID, PID, PPID, CPU usage, start time, TTY, and command)

Alternatively, a more detailed output can be obtained with:

ps aux

• -a : Shows information about all users
• -x : Shows information about processes without terminals
• -u : displays the process for a specific user.

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1.2 Explore the Function of the Following Commands

cat Command

The cat (concatenate) command is a basic utility used to read, combine, and write file contents.

Functions:

• Display the contents of one or more files to standard output.
• Concatenate multiple files.
• Create or overwrite files via redirection.
• Append data to existing files.

Examples:

# Show contents of file.txt
cat file.txt

# Show contents of file1.txt followed by file2.txt
cat file1.txt file2.txt

# Show contents with line numbers
cat -n file.txt

# Copy contents of file.txt to new.txt (overwrite)
cat file.txt > new.txt

# Append contents of file.txt to new.txt
cat file.txt >> new.txt

# Create a new file using standard input (Ctrl+D to save)
cat > test.txt

Note: While cat can create files, editors like vim or nano are more suitable for interactive editing.

file Command

The file command determines a file's type by examining its contents rather than relying on the file extension.

Functions:

• Identify file types (text, binary, executable, archive, media, etc.).
• Detect encodings and binary formats.

Examples:

# Identify the type of a file
file myfile

# Check multiple files
file file1 file2

# Show MIME type
file --mime-type image.png

Example output:

route Command

The route command displays or modifies the system's IP routing table.

Functions:

• View current routing information.
• Add or delete network routes.

Examples:

# Display routing table
route -n

# Add a default gateway
sudo route add default gw 192.168.1.1

# Delete a route
sudo route del default

nice Command

The nice command is used to start a process with a specific scheduling priority.

Functions:

• Adjust process priority at startup.
• Influence CPU scheduling without stopping the process.

Examples:

# Run a command with lower priority
nice -n 10 myscript.sh

# Check priority (NI column)
top

Lower nice values mean higher priority. Only root can assign negative values.

grep Command

The grep command searches for patterns in text using regular expressions.

Functions:

• Search text in files or command output.
• Filter command results.
• Support regular expressions.

Examples:

# Search for a word in a file
grep "error" log.txt

# Case-insensitive search
grep -i "warning" log.txt

# Recursive search
grep -r "TODO" src/

gunzip Command

The gunzip command decompresses files compressed with gzip.

Functions:

• Decompress .gz files.
• Restore original file contents.

Examples:

# Decompress file.gz
gunzip file.gz

# Keep original compressed file
gunzip -k file.gz

netstat Command

The netstat command displays network connections, routing tables, and interface statistics.

Functions:

• View open ports and active connections.
• Display listening services.

Examples:

# Show all listening ports
netstat -tuln

# Show active connections
netstat -an

sed Command

The sed (stream editor) command performs text transformations on input streams.

Functions:

• Search and replace text.
• Edit files non-interactively.
• Process text pipelines.

Examples:

# Replace 'foo' with 'bar'
sed 's/foo/bar/' file.txt

# Replace globally
sed 's/foo/bar/g' file.txt

# Edit file in-place
sed -i 's/foo/bar/g' file.txt

top Command

The top command provides a real-time view of system processes and resource usage.

Functions:

• Monitor CPU and memory usage.
• View running processes dynamically.
• Manage process priorities interactively.

Examples:

# Start process monitor
top

Useful interactive keys:

• k kill a process
• r renice a process
• q quit

bg Command

The bg command resumes a stopped job in the background.

Functions:

• Continue suspended jobs without occupying the terminal.
• Works with job control in shells.

Examples:

# Suspend a running process
Ctrl+Z

# Resume it in the background
bg

# Resume a specific job
bg %1

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1.3 Create basic linux commands for the following tasks

Locate the executable files or location of a program from the file system.

Locates the executable of the gcc command.

Display the starting content of a file

Shows the first 10 lines of big.txt.

Determine the path along which a packet travels

traceroute <destination>

Display IP Address, Hardware and MAC address. It is also used configure network interfaces

ip addr

Stop a process

kill <PID>

Search for all .conf files under /etc

sudo find /etc -name '*.conf'

Display CPU and memory usage of a process

top

Alternatively, for a specific process:

top -p <PID>
# Or
ps -p <PID> -o %cpu,%mem,cmd

Display routing table

route -n
# or
ip route

Trace the path to www.google.com

traceroute www.google.com

Redirect the output of ls to a file files.txt

ls > files.txt

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1.4 Employ Commands Used to Manage a Linux Server

Copy multiple files and directories

cp file1 file2 /destination/

Copy directories recursively:

cp -r dir1 dir2 /destination/

Take a backup for an existing file

cp file.txt file.txt.bak

Remove duplicate lines of a file

sort file.txt | uniq

Overwrite file with unique lines:

sort file.txt | uniq > clean.txt

View only active connections

netstat -an | grep ESTABLISHED

Search for a particular information inside a text file

grep "keyword" filename.txt

Compress a directory into a .tar.gz backup

tar -czvf backup.tar.gz directory/

Show last 50 lines

tail -n 50 filename.txt

Show kernel version

uname -r

Locate a program's path

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1.5 Use Core Linux Commands

Display the first 30 lines of a file named logs.txt

head -n 30 logs.txt

Start a program with lower priority (nice value = 10)

nice -n 10 script.sh

Display all processes running under the user root

ps -u root

Full format:

ps -u root -f

Count how many words are inside the file report.txt

wc -w report.txt

List all processes that are running in the background for the current user

jobs

Display the file content in reverse order

tac filename.txt

Query DNS to fetch the IP address or domain name from DNS records

nslookup domain.com

Alternative:

dig domain.com

Change the hostname of the server

hostnamectl set-hostname new-hostname

Show the parent process ID (PPID) of a process with PID 2000

ps -o ppid= -p 2000

Remove duplicates and save into a new file

sort file.txt | uniq > unique.txt