Processes

(Usage hints for this presentation)

IT Systems, Summer Term 2024
Dr. Jens Lechtenbörger (License Information)

Chair of Data Science: Machine Learning and Data Engineering (Prof. Gieseke)
Dept. of Information Systems
University of Münster, Germany

1. Introduction

1.1. Core Questions

What is a process?
How are files represented by the OS, and how are they used for inter-process communication?

(Based on Chapter 7 and Section 8.3 of (Hailperin 2019))

1.2. Learning Objectives

Explain process and thread concept
Perform simple tasks in Bash (continued)
- View directories and files, build pipelines, redirect in- or output, list processes with ps
Explain access control, access matrix, and ACLs
- Use chmod to modify file permissions

1.3. Retrieval practice

1.3.1. Previously on OS …

What are processes and threads?
What is a thread control block?
What are system calls?
How to execute shell commands as part of The Command Line Murders?

1.3.2. Quiz 1

1.3.3. Quiz 2

1.3.4. Quiz 3

Agenda

1. Introduction
2. Processes
3. File Descriptors
4. Access Rights
5. Conclusions

2. Processes

/proc

2.1. Processes

First approximation: Process ≈ program in execution
- However
  - Single program can create multiple processes
    - E.g., web browser with process per tab model
  - What looks like a separate program may not live inside its own process
    - E.g., separate GNU Emacs window showing PDF file via PDF Tools
    - (Window contents might be produced with help of different process, though)
Processes are central management units of OSs. As you already know, you can think of a process as a program in execution. E.g., if you open an app on your phone, this app is usually managed as a process by the OS. Also, if you use a command line (as in The Command Line Murders), the command line itself is one process (whose instructions are executed in the context of a virtual address space), while commands such as grep lead to the creation of new processes (with their own instructions and address spaces).

However, as you have seen already, the picture is more complicated as some “apps” may really be managed with multiple processes by the OS, while also a single process may provide functionality that looks like multiple “apps”.

Reality: Process = Whatever your OS defines as such
- Unit of management and protection
  - One or more threads of execution
  - Address space in virtual memory, shared by threads within process
  - Management information in process control blocks
    - Access rights
    - Resource allocation
    - Miscellaneous context

2.2. Process Creation

OS starts
- Check your OS’s tool of choice to inspect processes after boot

User starts program
- Touch, click, type
Processes start other processes
- POSIX standard with Process management API; see (Hailperin 2019)

2.2.1. Bash as Command Line

Recall: Command line as interface to OS to execute processes
- Unix command line historically called “shell”
  - Command line itself is a process
  - Lots of shell variants; Bash from The Command Line Murders used here
A command line, or shell, runs as process and provides a textual user interface, with which more processes can be executed. We only consider the Bash in this course.
- Command line can (1) execute builtin commands and (2) create processes for other commands
  1. Builtin commands are executed internally
    - Type help to execute one and see all of them
  Importantly, not every typed command leads to the creation of a new process. Instead, every shell offers a set of builtin commands, which are executed internally, as part of the shell’s process. Execute the builtin command help to learn more.
  1. Programs are executed as new child processes (requires system calls)
    - E.g., cat, grep, less, man, ps
    - By default, while child process for program runs, process of bash waits (not on CPU but blocked) for return value of child
  In addition, every operating system comes with programs, and those programs can also be executed from the shell, to be managed as processes by the OS. In GNU/Linux, we expect a standard set of preinstalled utility programs, e.g., the ones listed here, but also text editors, web browsers, games, etc.
  
  If you execute a program, then by default the process of the command line is blocked, waiting for a return value from a new child process that runs the program.

2.3. Process Control Block

Similarly to thread control blocks the OS manages process control blocks for processes
- Numerical IDs (e.g., own and parent)
- Address space
- Resources (shared by threads)
  - E.g., file descriptors discussed next
- Security information
  - Related to access rights
- And more, beyond course, e.g.:
  - Interprocess communication with signals

Similarly to thread control blocks for threads, the OS manages process control blocks for processes.

Typical pieces of information are listed here, including numerical identifiers for the process itself and its parent process; management information for virtual memory, for resources such as files, to manage access rights, and signals for communication between processes.

Note that the process control block collects information that is shared by all threads of the process, while thread control blocks are about information that is specific to each thread.

Of course, implementations across OSs differ considerably. Beyond class goals, the Linux kernel, for example, uses the same structure for process control blocks and thread control blocks, where process information shown on this slide is only stored once in memory. Such memory areas are then referenced with pointers from all thread control blocks that share the same information.

2.3.1. Seeing Processes and Threads on Linux

Linux kernel offers /proc (drawing) (man page offers details)
- Pseudo-filesystem as interface to Linux kernel data structures
  
  On Linux systems, the directory /proc is a so-called pseudo-filesystem. It looks and feels like any other directory, but it does not contain “real” files. Instead, it exports kernel management data through the interface of a filesystem.
  
  On other systems, this directory may be missing or be incomplete.
  - Subdirectories per process ID (e.g., /proc/42) with details of process control block for process with ID 42
    
    For example, every process and every thread has a numeric identifier, ID for short, and you find a subdirectory under /proc for these numbers. In turn, files and directories in that subdirectory show management information including details of process and thread control blocks.
    
    On a side note, the ID assigned to the first thread of a process is equal to the process ID.
- Process listing command ps inspects /proc
  - (Use man ps for implementation-specific details, following options are for GNU/Linux)
  - ps -e shows some details on all processes (IDs, time, etc.)
    - Option -L adds thread information, option -f for “full format”, e.g.: ps -eLf
    - (“L” for “light weight process”, a synonym for thread; column LWP shows thread IDs)
    On GNU/Linux, the command ps lists running processes, and it does so by inspecting the directory /proc. As usual, the manual page contains all details about the command. In particular, it uses “light weight process” as synonym for “thread”.
    
    By default, threads are not shown in ps output, but you need an extra option as suggested on the slide.
  - ps -C <name> shows some details on all processes with the given name
    
    Depending on the implementation of ps, you may also be able to display only information related to processes with a known command name as shown here.
    
    If that option is not available in your implementation, you can pipe the output of ps to grep. In the grep output, column headers are filtered out. Thus, check without grep first, and take note of column headers. (E.g., for Cygwin or Mac OS.)

Other OSs come with their own tools

3. File Descriptors

Recall The Command Line Murders
1. cd clmystery/mystery
2. head crimescene | grep Alice
  - crimescene \(\leadsto\) head \(\leadsto\) grep \(\leadsto\) console output
3. head crimescene > first10lines
  grep Alice < first10lines
  - crimescene \(\leadsto\) head \(\leadsto\) first10lines \(\leadsto\) grep \(\leadsto\) console output
(Files are covered in Section 8.3 of (Hailperin 2019))

Files are a common OS abstraction to organize data as named streams of bytes that are stored persistently. Persistence means that files should keep their data beyond crashes and power failures.

(As a side note, we can also create file systems in RAM, whose contents are forgotten, when power is turned off…)

As you experienced in the context of The Command Line Murders, file systems provide a hierarchically organized name space, where files are located in directories. (In fact, directories are just files with special properties, but we do not go into details here.)

In the context of The Command Line Murders, you saw that files can serve as inputs and outputs of processes and that one process can communicate its output with the pipe symbol as input to another process. Thus, you are able to explain how the commands shown under items (2) and (3) here produce the same final output. The bullet points underneath the commands are supposed to visualize the flow of data with squiggly arrows, where files are shown in blue, commands in black.

(Please think about differences and commonalities: Both create one process for head and one for grep. One requires more typing than the other. One requires the creation of an additional file, which is left around and may or may not be relevant afterwards…)

3.1. File Descriptors

OS represents open files via integer numbers called file descriptors

Processes invoke system calls to open files and to work on files’ contents. The OS represents each file opened by a process with a file descriptor, which is just an integer number that is returned from the system call that opened the file. Afterwards, processes invoke further file operations with system calls on such file descriptors, e.g., read and write.

Importantly, file descriptors are local to processes. Thus, the same number, say 5, may refer to file instructions for one process but to another file for a different process; in fact, for some processes, 5 may not be a valid file descriptor at all.
- Files are abstracted as named streams of bytes
Each file has a name, and is just used as stream of bytes, regardless of its format and contents. E.g., a text file is a stream of characters, while a movie file contains binary data, both of which are accessed in the same way.
- File abstraction includes “real” files, directories, devices, network access, and more
  - Typical operations: open, close, read, write
  Importantly, the file abstraction offers a uniform interface to all kinds of data sources, including directories and network connections.
  
  Typical operations on files are open, close, read, and write, offered by system calls. Here, open returns a new file descriptor for some file. That file descriptor can then be used subsequently to read or write from the file.
- POSIX standard describes three descriptors (numbered 0, 1, 2) for every process
  “Standard file descriptors” by Jens Lechtenbörger under CC BY-SA 4.0; using UXWing icons: keyboard, monitor, operations; from GitLab
  1. Standard input, stdin (e.g., keyboard input)
  2. Standard output, stdout (e.g., print to screen/terminal)
  3. Standard error, stderr (e.g., print error message to terminal)
  The POSIX standard specifies three file descriptors for every process, which are numbered 0, 1, and 2.
  
  File descriptor 0 is called standard input, and reading from it can be used for keyboard input on the command line.
  
  File descriptor 1 is called standard output, and writing to it can be used to print output on the command line.
  
  File descriptor 2 is called standard error, and writing to it can be used to print error messages. So, both, standard output and standard error can print to the command line.
  
  As a programmer, you need to decide what to print where (if at all). You should choose standard output for ordinary output of your program, and standard error for error messages. Those two types of messages can then be distinguished semantically and, e.g., be sent to different files via redirection or to different consumers in general.

3.2. Drawing on File Descriptors

File descriptors

3.3. Files/Streams for IPC

IPC = Inter-process communication
- Communication between processes
- Files and streams enable communication
  - (Next to other mechanisms, e.g., shared memory, signals, networking)

Files can be used for interprocess communication, where different processes communicate by reading and writing on the same file or set of files.

As side note, other mechanisms for communication between processes exist as well. E.g., with shared memory, some frames may be embedded into virtual address spaces of several processes, giving up address space isolation for specific purposes, e.g., to share code or data structures between processes.

Also, processes can send signals to each other (via the OS). You may know this from the kill command, which allows users to terminate running processes. Actually, this command can send different signals, which is beyond the scope of our course.

With networking functionality, even processes on different computers can communicate with each other, e.g., web browsers and web servers.

Files provide persistent storage
- Written/created by one process
- Potentially accessed by other processes, communication, e.g.:
  - Files with source code
    - Write source code in editors (over time, different processes)
    - Perform quality checks on source files with specialized tools (other processes, maybe passing results to editor)
    - Compile source code to executable code
  - Collect log messages from several processes in one file; analysis of file contents with alerting by separate process

3.4. Redirection of Streams

Streams of bytes can be redirected
- E.g., send output to file instead of terminal
  - head names.txt > first10names.txt
    - (Recall: This command occurs in cheatsheet of Recall The Command Line Murders)
  - Code for head invokes system calls
    - open file names.txt, results in newly allocated file descriptor
    - read from file descriptor for names.txt
    - write to stdout (opened automatically by default)
  - Operator > redirects stdout of process to file first10names.txt
Here you see some details about a command which you know from The Command Line Murders.

The program head accesses a file and prints some output, by default on the commend line. In terms of file descriptors, it asks the OS to open the input file, which results in a newly allocated file descriptor, i.e., some number larger than those of the standard file descriptors, which in turn can then be used to read contents of the file. The program really writes its output to stdout, which the command line by default prints in the terminal. With the output redirection shown here, stdout is redirected to a file.
- Also, lots of commands can access data on stdin
  - head < names.txt
    - Operator < redirects file to stdin of process; here, access of names.txt via stdin
Programs may also be able to access input on stdin, and head is an example for such programs: When no file name is passed as argument, head reads from stdin, i.e., from file descriptor 0. With the input redirection shown here, head will see the contents of the file on stdin.

3.5. Streams for IPC

Processes can communicate with pipelines/pipes
- One process connects stream as writer into pipeline
- Second process connects stream as reader from pipeline
- Pipelines (and files) are passive objects (used by processes)
E.g., send stdout of one process to stdin of another
- head names.txt | grep "Steve"
  - (Recall: This pipeline occurs in cheatsheet of The Command Line Murders)
  - Here, process for head sends its stdout via pipe operator (|) to stdin of process for grep
    - In contrast to files, pipes do not store data persistently

3.5.1. Drawing on Pipes

Pipes

3.6. File Descriptors under `/proc`

For process with ID <pid>, subdirectory /proc/<pid>/fd indicates its file descriptors
- Entries are symbolic links pointing to real destination
  
  In a dedicated subdirectory for each process under /proc, file descriptors in use by the process are shown as so-called symbolic links. You can think of a symbolic link as an additional name, which points to some file or device.
  
  On Mac OS, listing file descriptors in this fashion does not work. As alternative, you can use a command to list open files shown in an earlier drawing.
- Use ls -l to see numbers and their destinations, e.g.:
```
lrwx------ 1 jens jens 64 Jun 26 15:34 0 -> /dev/pts/3
lrwx------ 1 jens jens 64 Jun 26 15:34 1 -> /dev/pts/3
lrwx------ 1 jens jens 64 Jun 26 15:34 2 -> /dev/pts/3
lr-x------ 1 jens jens 64 Jun 26 15:34 3 -> /dev/tty
lr-x------ 1 jens jens 64 Jun 26 15:34 4 -> /etc/passwd
```
  - Use of /dev/pts/3 (a so-called pseudo-terminal, which represents user interaction with the command line) for stdin, stdout, and stderr
  - Access of file /etc/passwd via file descriptor 4
  - (If you are curious: /dev/tty is mostly the same as /dev/pts/3 here)
E.g., here we see five file descriptors used by some process, numbered from 0 to 4, where the symbolic link with the name 4 points to a file passwd, which contains user information under GNU/Linux.

We also see that the standard file descriptors all point to the same device, which represents user interactions with the command line; details are not important here.

3.6.1. A Quiz

4. Access Rights

4.1. Fundamentals of Access Rights

Who is allowed to do what?

Access rights determine who is allowed to do what.

System controls access to objects by subjects
- Object = whatever needs protection: e.g., region of memory, file, service
  - With different operations depending on type of object
- Subject = active entity using objects: process
  - Threads of process share same access rights
  - Subject may also be object, e.g., terminate thread or process
  With that goal, the OS controls accesses to objects by subjects. Here, objects can be of varied types, such as memory, files, or services, while subjects are processes. The threads of a process then share the access rights of a process.
- Subject acts on behalf of principal
  - Principal = User or organizational unit
  - Different principals and subjects have different access rights on different objects
    - Permissible operations
The process is created by some user, maybe as part of an organizational unit, who is called principal.

Importantly, different principals and subjects have different access rights on different objects, where the access rights specify what operations are permitted on a given object for a given subject.

As simple example, consider a document with tasks for the next written exam, created by a team of instructors on a multi-user computer. Clearly, that team should be allowed to read and write the exam document, while students must not have any permissions on that document at all. In contrast, students may be allowed to read documents of selected previous exams, but not to modify them.

4.1.1. Typical Access Right Operations

In general, dependent on object type, e.g.:
- Files
  - Create, remove
  - Read, write, append
  - Execute
  - Change ownership
For different types of objects, different operations are permitted or restricted by access rights. For example, on files, operations such as create, remove, read, write, append, execute, or change of ownership may be applicable.
- Access rights
  - Copy/grant
Access rights themselves may also be considered as objects under access control. Thus, some subjects may be allowed to copy access rights or to grant access rights to other subjects.

4.2. Representation of Access Rights

Conceptual: Access (control) matrix
Slices of access matrix
- Capabilities
- Access control lists

4.2.1. Access (Control) Matrix

Matrix
- Principals and subjects as rows
- Objects as columns
- List of permitted operations in cell

4.2.2. Access Matrix: Transfer of Rights

Transfer of rights from principal JDoe to process P_1
- Figure 7.12 (a) of (Hailperin 2019): copy rights
  
  F_1 F_2 JDoe P_1 …
  
  JDoe read write
  
  P_1 read write
  
  ⋮
This small excerpt of an access matrix demonstrates the representation of access rights in general. John Doe and process 1 are listed as principal and subject in separate rows, while objects are listed in columns. More specifically, the columns list two files and again principal John Doe and process 1.

Note that principal and process occur in column headers as well as row headers, indicating that they serve dual roles as objects and subjects. Access right of process 1 (as subject) are indicated in the row for process 1. You see that the process is allowed to read file 1 and write file 2. You also see that John Doe and process 1 share the same access rights.

Processes obtain their access rights from principals on whose behalf they are operating. For example, if you and me have got user accounts on my machine and if both of us start the same text editor, then the two processes for these text editors will have different access rights, which are derived from our (users’) access rights: Typically, you will be able to read and write your own files, while you should be unable to access my files, and vice versa.

In this example, process 1 is working on behalf of principal John Doe, and the rights of John Doe were simply copied to process 1, when that process was created by John Doe.
- Figure 7.12 (b) of (Hailperin 2019): special right for transfer of rights
  
  F_1 F_2 JDoe P_1 …
  
  JDoe read write
  
  P_1 use rights of
  
  ⋮

4.2.3. Capabilities

Capability ≈ reference to object with access rights
Conceptually, capabilities arise by slicing the access matrix row-wise
- Principals have lists with capabilities (access rights) for objects
- Challenge: Tampering, theft, revocation
  - Capabilities may contain cryptographic authentication codes

4.2.4. Access Control Lists

Access Control List (ACL) = List of access rights for subjects/principals attached to object
Conceptually, ACLs arise by slicing the access matrix column-wise
- E.g., file access rights in GNU/Linux and Windows (see Sec. 7.4.3 in (Hailperin 2019))

4.2.5. File ACLs

ls lists files and directories
- With option -l in “long” form
  - Shortened ACLs
    - Permissions not for individual users; instead, separately for owner, group, other
    - Owner: Initially, the creator; ownership can be transferred
    - Group: Users can be grouped, e.g., to share files for a joint project
    - Other: Everybody else
  - File type, followed by 3 triples with permissions
    - File (-), directory (d), symbolic link (l), …
    - Read (r), write (w), execute (x) (for directories, “execute” means “traverse”)
    - Set user/group ID (s), sticky bit (t)
  - ls -l /etc/shadow /usr/bin/passwd
    - - rw- r-- --- 1 root shadow 2206 Jan 11 2024 /etc/shadow
    - - rws r-x r-x 1 root root 68208 Feb 6 13:49 /usr/bin/passwd*
  - ls -ld /tmp
    - d rwx rwx rwt 14 root root 20480 Jun 8 13:20 /tmp

The command ls can display access control lists on files in GNU/Linux. The long listings produced with option -l show permissions in the form of three triples. The first triple specifies what the “Owner” is allowed to do, the second one is for a “Group”, the third one for “Others”.

In general, the owner is the user creating a file, but ownership can also be transferred.

Users can also be grouped, e.g., to share files for a joint project. Groups are created by the administrator, with a many-to-many relationship between users and groups. Each file is assigned to one group, and files’ groups can be changed by their owners.

If a user is neither the owner nor a member of the group for a file, then “other” permissions apply.

In two ls outputs here, we see permissions for two files, namely shadow and passwd, and for the standard temporary directory /tmp.

Both files are owned by root (in red), who is the default administrator on GNU/Linux. The file shadow contains hashed user passwords, and passwd is the command with which users can change their passwords. Clearly, users must not be able to change passwords of other users (except for root who can do whatever she likes).

Let us look at the triples of permissions to see how this goal is achieved. The triples may contain letters to indicate read (r), write (w), and execute (x) permissions, with hyphens indicating missing permissions.

First, the permissions for file shadow can be interpreted as follows:

The owner triple (in red) specifies that root is allowed to read and write but not to execute the file. (As this file just contains data, execution does not make sense.)

Next, group members (in blue) are allowed to read but neither to write nor to execute. Here, the group is shadow, which is not important for us. (See this hyperlink if you are interested.)

Finally, others (in green) do not have any permission.

Thus, only root can write to shadow (w is only present in red for the owner, while blue and green parts do not contain that letter). So how can users change their own passwords, which requires updates of the file shadow?

We see that everyone is allowed to read and execute passwd, which is the command that allows users to change their passwords. Usually, when a user executes a command, the resulting process runs with the permissions of the executing user. Here, however, we see an s for “set user ID” in red. With this permission, the OS will run the process for passwd with permissions of the file’s owner, that is root. Thus, the process for passwd has write permissions of root on shadow. (Of course, passwd needs to make sure that users only change their own passwords.)

In the directory /tmp, everybody is allowed to read and write. With the green so-called sticky bit t, users are only allowed to delete their own files, not those of other users.

4.2.6. Drawing on File ACLs

Unix permissions

4.2.7. File ACL Management

Management of ACLs with chmod
- Read its manual page: man chmod
- (Default permissions for new files are configurable)
  - (Beyond class topics, see help umask in bash)
Permissions with bit pattern or symbolically
- Previous drawing illustrates bit patterns for r, w, x
- Symbolic specifications contain
  - one of (among others) u, g, o for user, group, others, resp.,
  - followed by + or - to add or remove a permission,
  - followed by one of r, w, x, s, t (and more)
- E.g., chmod g+w file.txt adds write permissions for group members on file.txt

5. Conclusions

5.1. Summary

Process as unit of management and protection
- Threads with address space and resources
  - Including file descriptors
- Isolation of virtual address spaces as protection mechanism
File access abstracted via numeric file descriptors as streams
- Redirection and pipelining for inter-process communication
Access control restricts operations of principals via subjects on objects
- GNU/Linux file permissions as example for ACLs
- Access control as additional OS protection mechanism

This presentation concludes the OS topics of our course.

The process is considered the fundamental unit of management and protection in operating systems. Each process has its own separate address space and resources, including file descriptors. Threads of a process share that address space and resources, and they form the units for scheduling.

The OS isolates the address spaces of different processes from each other, which prevents unauthorized access or manipulation of data belonging to one process by other processes. In addition, it also protects data structures of the OS itself.

File descriptors serve to abstract file access, allowing processes to interact with files using numerical identifiers instead of physical locations. This abstraction enables powerful features such as redirection and pipelining, which can be used for inter-process communication.

Many OSs implement access controls on objects such as files. These controls restrict certain operations by principals acting through subjects. For instance, file permissions are enforced through access control lists that determine what actions individual users and their processes may perform on specific files. With these settings, administrators and users can help prevent unwanted modifications or disclosures of sensitive information.

5.2. Perspective

Different access control paradigms exist
- Discretionary access control (DAC)
  - Owner grants privileges
  - E.g., file systems, seen above
- Mandatory access control (MAC)
  - Rules/policies about properties of principals, processes, resources define permitted operations
    - E.g., SELinux, AppArmor
    - More complex to manage/use but “more secure”
- Role based access control (RBAC)
  - Permissions for tasks bound to organizational roles
    - E.g., different rights for students and teachers in Learnweb

Beyond what you saw in this presentation, different access control paradigms exist. File permissions, as presented above, fall under discretionary access control. Here, the owner of a resource needs to define access restrictions or to grant privileges. As users are typically lazy and as their options are limited, this approach is error prone.

More secure systems rely on mandatory access control, MAC for short, e.g., with SELinux. Here, a set of policies defines who is allowed to do what. E.g., the root user is not allowed to do everything any longer. Also, processes started by a user do not inherit user permissions any more, but can be limited, e.g., in terms of permissions on files and directories or regarding network access. Then, if an exploitable security flaw exists in software, it will still be restricted by MAC.

Finally, access control is often tied to roles instead of individual users. E.g., in Learnweb, different roles such as guest, student, and lecturer exist, which come with different privileges.

5.3. In-class: Safety vs Security

Selected pointers
- Safety: Protection against unintended/natural/random events
  - Requires proper management, involves training, redundancy (e.g., hardware, backups), and insurances
- Security: Protection against deliberate attacks/threats
  - Protection of security goals for objects and services against attackers
  - Security goals and risk
    - CIA triad with classical goals: Confidentiality, Integrity, Availability
    - Many more, e.g., accountability, anonymity, authenticity, (non-) deniability
  - E.g.: Processes on “your” system?
    - Advanced persistent threats (APTs), rootkits
    - Check externally, e.g., German Desinfec’t
- Design processes and management
  - E.g., BSI in Germany and ISO standards: IT-Grundschutz

This slide points to the general concepts of security and safety in IT systems, which are not covered in this course. They will be briefly addressed in class.

Every IT system needs to be protected against failures or other negative consequences that arise from unintended events, which concerns the safety of the system, and deliberated attacks, which concerns security.

In organizational settings, safety and security require design processes and proper management, for which national and international standards with recommendations and best practices exist.

You may want your own systems to be safe and secure as well. Then, probably most importantly, create backups, and make sure that you can restore them. Afterwards, check out terms such as advanced persistent threats and rootkits.

In our Bachelor’s program, a separate module addresses information security in the context of distributed systems.

Bibliography

Hailperin, Max. 2019. Operating Systems and Middleware – Supporting Controlled Interaction. revised edition 1.3.1. https://gustavus.edu/mcs/max/os-book/.

License Information

Source files are available on GitLab (check out embedded submodules) under free licenses. Icons of custom controls are by @fontawesome, released under CC BY 4.0.