Advanced Programming in the UNIX Environment

An illustration of how permission octal modes and umasks work.

Advanced Programming in the UNIX Environment

Week 3: umask(2)

In this video lecture, we'll take a look at what file ownership and permissions are applied when we create a new file. In the process, we'll learn about the concept of a process's "umask", and look at how the 'umask' shell built-in is implemented.

https://youtu.be/bRAR2bv2HSM

@Harald @midtsveen

Was experimenting with Debian on my iBook around that time, but switched to Mac OS X as it was supposed to #justwork .

Spent two entire weeks on an important document using Apple Pages.

And because of a fundamental bug with no workarounds, in the end I could not export to PDF or print or do anything useful with it.

That was the day I began to learn how to use LaTeX…

Advanced Programming in the UNIX Environment

Week 3: chmod(2) and chown(2)

Having seen a lot of examples in our previous videos of creating files, changing their ownership, changing their permissions, we now focus on the system calls that are used to implement the chmod(1) and chown(8) commands.

https://youtu.be/5MJmCanZDyk

Advanced Programming in the UNIX Environment

Week 3: struct stat st_mode

In this video segment, we're looking at how the permissions defined in the `struct stat st_mode` are applied. You want to pay particular attention to the permissions on directories and the order in which they are checked.

https://youtu.be/vS6abFjN3ZY

Advanced Programming in the UNIX Environment

Week 3: UIDs intro

In this video lecture, we'll learn a little bit more about file ownership and the user IDs of a process (real, effective, saved) by looking at the seteuid(2) and setuid(2) system calls and experimenting with setting the setuid bits and observe the file access we gain.

https://youtu.be/YlcF3ncTQpo

Advanced Programming in the UNIX Environment

Week 3: stat(2) intro

In this video lecture, we meet our new best friend, the 'struct stat'. We'll cover the stat(2) system calls and begin discussing each of the fields in the struct, often by example of the ls(1) and stat(1) commands. In this way, we begin learning more about how the Unix File System is implemented.

https://youtu.be/veFwXrEHPsk

Advanced Programming in the UNIX Environment

A we're starting to regularly write C code now, it might be good to share a few useful links:

How to C (as of 2016)
https://matt.sh/howto-c

A critique of "How to C" by Matt:
https://github.com/Keith-S-Thompson/how-to-c-response/blob/master/README.md

and, even though you kids don't have any idea what Usenet is (now get off my lawn), the comp.lang.c FAQ:
https://c-faq.com/

Advanced Programming in the UNIX Environment

Week 2: File Sharing

In this final video lecture segment for our week 2 materials, we take a look at what it means when multiple processes access the same files and what the implications of that are on the syscalls we know. We conclude with a look at /dev/fd on different operating systems, including #NetBSD, #macOS, and #Linux

https://youtu.be/CAbUtc86ULw

Advanced Programming in the UNIX Environment

Week 2: read(2)/write(2)/lseek(2)

In this video lecture, we will go into the details of the read(2), write(2), and lseek(2). We'll also do a few weird things with file descriptors, and take a look at how we can ensure I/O efficiency when making these system calls.

https://youtu.be/EUUPw8MOV_A