/How-linux-works-Study-Notes

Notes of "How Linux Works 2nd Edition"

Chapter 1: The Big Picture

General linux system organization:

  • User Processes (GUI, servers, shell)
  • Linux Kernel (system calls, process mgmt, memory mgmt, device drivers)
  • Hardware (cpu, ram, disks, network ports)

kernel mode: no restrictions to cpu and memory
user mode: parts of memory + safe cpu operations

kernel's job:

  • manage process
  • manage memory
  • system calls
  • device drivers

kernel keeps the snapshot of memory and cpu state during context switch.
cpu runs in kernel mode to switch processes for cpu to work on

fork() -> create a copy of the process
exec() -> replace the process with new one

all user process in linux starts with fork() except for init process

ls in shell works like this:

  • shell fork() creating a copy of shell
  • that copy exec(ls) replacing the process with ls

Chapter 2: Basic Commands and Directory Hierarchy

ioli@bipin:~$ find /usr/share -name words  
/usr/share/dict/words

grep, find, diff, file

making shell variable an env variable:
$ VARIABLE=value
$ export VARIABLE

modifying PATH env variable:
PATH=$PATH:newdir
appends the PATH variable

Terminal keyboard shortcuts:
CTRL-A : move to the start of line
CTRL-E : move to the end of line
CTRL-U : delete whole line backward

Search manual by keyword:
$ man -k keyword

Detail and conceptucal documentation:
$ info command

Redirect to file:
overwrite file: $ command > file
append to file: $ command >> file

Redirect stdout to outfile and stderr to errorfile:
$ command > outfile 2> errorfile

Redirect stderr to same as stdout:
$ command > logfile 2>&1

double dollar gives the pid of current shell
$ ps u $$

freeze the process
$ kill -STOP pid
resume the process
$ kill -CONT pid

suspended processes
$ jobs
resume by bringing to foreground
$ fg
resume in background
$ bg

compress
$ gzip file
decompress
$ gunzip file.gz
archive
$ tar cvf archive.tar file1 file2 file3 ..
unpack archive
$ tar xvf archive.tar

decompressing compressed archive
$ gunzip archive.tar.gz
check what files are there in archive
$ tar tvf archive.tar
extract from archive
$ tar xvf archive.tar

pipelined way of decompressing compressed archive
$ gunzip -c archive.tar.gz | tar xvf -

Chapter 3: Devices

device files:
b : block device (eg. disks)
c : character device (eg. printer)
p : pipe device
s : socket device