Soma-notes - User contributions [en]

Operating Systems 2017F Lecture 6

2017-10-04T04:53:56Z

Jamesklau:

==Video==

Video from the lecture given on September 26, 2017 [http://homeostasis.scs.carleton.ca/~soma/os-2017f/lectures/comp3000-2017f-lec06-26Sep2017.mp4 is now available].

==Code==

Code and files from the lecture (captured as they were at the end) are available [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/lec06/ here].

==Notes==
====What is a tar file?====
* A tar file stands for tape archive

====Building a Kernel====
*Check the current version
**Cd linux-source-4.4.0

*To become root
**Sudo su -

*To configure a linux kernel:
**Make menuconfig : to set options with an interface
**Make localmodcomfig : to create a configuration based on modules loaded
**Make oldconfig : to use a previously generated .config (cd/boot)
**Ls mod: list all the mod that are loaded (only built)

*To build a configured kernel from source:
**Make: build the main kernel
**Make modules: build the modules

*To install a built kernel:
** Sudo make install: put the kernel in /boot
**Sudo make modules_install: puts the module in appropriate directory
**Update-grub: tell the boot loader(grub) about the mew kernel and makes it bootable

*Reboot to run the new kernel:
**Sync
**Sudo shutdown -r now

*Check the version: Cat /proc/version

====Dynamic linking====
*Brk: allocates space from the kernel
*It is smaller in disk but bigger in memory
*It shared library

Operating Systems 2017F Lecture 5

2017-10-04T04:46:25Z

Jamesklau:

==Video==

Video from the lecture given on September 21, 2017 [http://homeostasis.scs.carleton.ca/~soma/os-2017f/lectures/comp3000-2017f-lec05-21Sep2017.mp4 is now available].

==Code==

Code and files from the lecture (captured as they were at the end) are available [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/lec05/ here].

==Notes==

====IO Redirection====
*The > operator output to a location
**Eg. Ls > foo.txt

*The | operator connect the output of the 1st program to the input of the 2nd program
**Eg. Shuf foo.txt | shuf > shuf2.txt (pipe operater connect output of shuf foo.txt to input of shuf then output to shuf2.txt)

*File usually comes with standard input (0), standard output(1),standard error(error message, port 2). This defined when program started
**Ls foo > test.txt 2 >error.txt: redirect error message (port 2) of foo to error.txt
*Ls foo>& all.txt: redirect everything to output file
**Bc -l: This command bring up the calculater

====Manipulating environment variables====

<syntaxhighlight lang="c">
int main(int argc, char *argv[], char *envp[]){
While (envp[i] != NULL) {
If (strcmp(“User=“, envp[i], 5){
printf(“%s\n”, envp[i]);
char *username = envp[i] +5; //pointer arithmetic
}
I++;
}
printf (“%s\n”, username);
return 0;
}
</syntaxhighlight>

*Getopt: a better way to find environmental variable

====Signals====
*Kill: send a signal to destroy a program
**Kill -stop 5617(This stop a progam) and Kill -cont 5617(resume a program)
**Sigkill, sigterm (ctrl+c), sigstop (ctrl+z), sigpipe (when | died), sighup (when close terminal window)
**Sigchild(when a child process terminated),

Operating Systems 2017F Lecture 3

2017-10-04T04:27:47Z

Jamesklau:

==Video==

Video from the lecture given on September 14, 2017 [http://homeostasis.scs.carleton.ca/~soma/os-2017f/lectures/comp3000-2017f-lec03-14Sep2017.mp4 is now available].

==Code==

Code and files from the lecture (captured as they were at the end) are available [http://homeostasis.scs.carleton.ca/~soma/os-2017f/code/lec03/ here].

==Notes==
====Commands ====
*-wall: show all warning
*less: allow screen navigation, hit q to quit

==== What is fork? ====
* Fork creates a new program but contains the same code (call the clone system call) and only argv[] and envp[] passed on to the new born program

==== What Happen to the child process after the parent process died? ====
*Every child process must have a currently running parent. When the parent process die, kernel collect the dead body(return value) and re-parent the process
* In the demo showed in class, “system d user” became its new parent
**Use command "Pstree" to show process hierarchy

==== What is zombie process? ====
*When a process die it become 'zombie' (s = sleep, z = zombie)
*We can use wait to be a 'good' parent

==== How to load a new binary manually====
*Use the execve command.
**We can fork child process to handle dangerous task (“Suicide Squad”), or handle all incoming request

==== Manipulating environment variables====
*argc tells the number of argument in command line, while argv[] contains the actual command obtained in the command line