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Lectures
Lecture 05 Template
05 - Intro to Linux
Outline
Goals
Interfaces
Internals
Source Code
Portable Operating System Interface (POSIX)
Standard Utility Programs
Standard Library
Announcements
Reading: MOS 10.2, LDD 1
Goals
Evolved from UNIX Goals (not predefined):
Torvalds started with his MINIX-based kernel, let
many other devs work on it, and Linux evolved via
natural selection from user feedback.
There are several levels of interfaces used to
interact and program in the Linux environment.
POSIX is published by IEEE and the Open Group
POSIX defines standard system calls, programming
interfaces (libraries), and shell programs (UI)
In "core services", among other things:
- Process creation and control
- Signals
- File system operations
- Pipes
- C library
- I/O port interface and control
- Process triggers
Also required:
- Synchronization primitives
- Threads (pthread)
- Shell
- etc.
Linux ships with a set of core set of utility
programs:
- File system manipulation
- Text filters
- Editors and compilers
- System administration
- Etc.
GNU C standard library provides functions from C
language definition
Kernel provides C definitions for system calls
System calls are special assembly
instructions and need to be exposed to C
language at compile time.
syscall() is defined in a header, but
implemented in assembly, symbol visible at
link-time.
(e.g. printf, scanf, etc.) see
(e.g. read, write, fork, etc.)
libc provides wrapper functions for convenience
on particular architectures.
POSIX requires C standard functions and UNIX
system calls to be defined, but not necessarily
defined by kernel.
The kernel is modular and generally organized
according to functionality.
The textbook presents a simplified view:
Realistically, there is a lot more going on.
Compiled kernel lives in /boot/vmlinuz-X.Y.Z
Source download:
Official Documentation:
We will install as a package:
Directory is 1.5 GB code -> 20 GB compiled
Interesting directories:
Useful exploration tools:
Bootlin (web-based code indexing tool)
Cscope (TUI code indexer/browser)
- Browse code of different Linux versions
- Search for symbols/identifiers
- Look up declarations and definitions
- Install:
- Index:
- Start:
- Exit:
- Search:
- C identifiers/symbols (e.g. start_kernel)
- Function/variable definitions
- Function calls
- Strings
- Usage:
- `tab`: switch between menu and results
- `arrows`: move between menu items
- `space`: see more results
- `enter`: search or select item (opens vi)
- Check source tree version:
- For a particular version:
- bootloader will allow you to select one
- see current version with `uname -a`
kernel.org/pub/linux/kernel/vX.Y/linux-X.Y.Z.tar.{gz|xz}
sudo apt install linux-source
make kernelversion
Examples from MOS Figure 10-2:
The current version is
These interfaces are mostly compliant with the
POSIX standard.
- Multiuser, modular, monolithic kernel
- Everything is a file
- Free and Open Source Software (FOSS)
But modern Linux does not adhere completely.
"UNIX Philosophy":
- Douglas McIlroy (invented the UNIX pipe)
- Make it easy to write, test, and run programs
- Economy/Elegance due to size constraints
- Constant maintenance & improvement
Write programs that do one thing and do it well.
Write programs that work together.
Write programs to handle text streams,
because that is a universal interface.
Interfaces
Internals
PA 1 is due today. I hope you started.
I will release PA2 instructions by tonight.
1)
2)
3)
Users
Standard Utility Programs
(shell, editor, compilers, etc.)
Standard Library
(open, close, read, write, fork, etc.)
Linux Kernel
(proc management, mem management, file system, I/O, etc.)
Hardware
(CPU, memory, disks, terminals, etc.)
User
Interface
Library
Interface
Syscall
Interface
MOS Figure 10-1
POSIX.1-2024
cat
chmod
cp
cut
grep
head
ls
make
od
paste
pr
ps
rm
rmdir
sort
tail
tr
mkdir
concatenate files and print on the standard output
change file mode bits
copy files and directories
remove sections from each line of files
print lines that match patterns
output the first part of files
list directory contents
GNU make utility to maintain groups of programs
make directories
dump files in octal and other formats
merge lines of files
convert text files for printing
report a snapshot of the current processes
remove files or directories
remove empty directories
sort lines of text files
output the last part of files
translate or delete characters
; Use the 'read' syscall (number 0) from stdin (fd 0)
mov rax, 0 ; syscall number for 'read'
mov rdi, 0 ; file descriptor 0 (stdin)
mov rsi, buffer ; address of buffer to store input
mov rdx, buffer_len; maximum number of bytes to read
syscall ; invoke kernel
see
Cygwin,
WSL1
C Standard
MOS Figure 10-3
Linux Kernel Map
interactive diagram
interactive map
Linux Kernel Archives
docs.kernel.org
arch/
ISA-specific code (boot process, context switch, etc.)
header files
kernel initialization code (not arch-specific)
memory management
device drivers
inter-process communication
file system
generic kernel core
networking
block memory devices
helper/utility libraries
config and compilation scripts
self-explanatory
function/mechanism examples
user space programs/scripts for debugging, tracing, etc.
include/
init/
mm/
drivers/
ipc/
fs/
kernel/
net/
block/
lib/
scripts/
Documentation/
samples/
tools/
sudo apt install cscope
make cscope
cscope
Ctrl-d