AMSA

Exam Example and Cheat-Sheet

Authors

Ferran Aran Domingo

Oriol Agost Batalla

Pablo Fraile Alonso

Week’s slides

Week	Non-Important Content (for exams)
0	Doesn’t count
1	Hardware and firmware (but software yes)
2	Interrupts, definitions and properties of kthreads / processes / threads, definitions of procfs
3	-
4	-
5	Virtual Space Layout (Stack, Heap, etc.)
6	-

Command Reference

Week	Command	Description	Mnemonics
1	`dmesg`	See Kernel logs	diagnostic message
1	`journalctl`	See systemd services (and kernel) logs	journal control
1	`systemctl <subcommand> <service>`	Manage a systemd unit (enable, start, status, etc.)	system control `<command>` `<service>`
2	`strace <command>`	See syscalls that `<command>` makes to the kernel	system trace
3	`nice -n <niceness> <program>`	Run `<program>` with given niceness (priority)	be nice with program
4	`kill -s <signal> <pid>`	Send a signal `<signal>` to process with PID `<pid>`	(no mnemonic — contra-intuitive)
4	`nohup <command>`	Ignore signal `SIGHUP` for `<command>`	no hang-up
5	`mkswap <file>`	Make `<file>` a swapfile	make swap
5	`swapon <file>`	Enable swapfile `<file>`	set swap on
5	`swapoff <file>`	Disable swapfile `<file>`	set swap off
6	`sudo <command>`	Run command as root	superuser do `<command>`
6	`groups <user>`	List which groups a user belongs to	-
6	`id <user>`	Show UID and GID for user	-
6	`useradd -m <username>`	Create a user with a home directory	add user
6	`groupadd <group>`	Create a group	add group
6	`passwd <user>`	Set a password for a user	password
6	`usermod -aG <group> <user>`	Add user to existing group `<group>`	user modify add to group
6	`su <user>`	Switch to user `<user>`	switch user
6	`whoami`	Display current user	-
6	`chmod <perm> <file \| folder>`	Change permissions for file or folder
6	`chown [user:group](user:group) <file \| folder>`	Change owner and group of file/folder
6	`lsblk`	List block devices (filesystems)	list block devices
6	`mkfs.<filesystem> <device>`	Format device with `<filesystem>`	make filesystem `<filesystem>`
6	`mount <device> <mountpoint>`	Mount device at mountpoint	-
6	`tune2fs -O quota <device>`	Enable quotas on device `<device>`	tune filesystem
6	`quotaon -v <mountpoint>`	Enable quota on `<mountpoint>`	-
6	`repquota <mountpoint>`	Show current quotas on `<mountpoint>`	represent quota
6	`setquota <options> <mountpoint>`	Set quotas with given options	-
6	`quotaoff <mountpoint>`	Disable quota on `<mountpoint>`	-

Exam Style

1) Decodifica, els següents permissos:

.rw-r--r-- pablo users  24 B  Mon Oct 27 10:09:32 2025 test.sh
.r-s--x--x root root 69 KB Wed Oct 29 08:46:57 2025 /run/wrappers/wrappers.2RNzlIuvsH/sudo

2) El meu sistema té poca RAM i el kernel de linux habitualment mata els programes donat que ocupen massa memòria anònima (pàgines del heap), que puc fer per arreglar-ho?

3) Estic intentant que el meu programa abarqui més temps de CPU

Estic executant:

$ nice -n -10 ./my_script.sh

I l’output és:

nice: cannot set niceness: Permission denied

Perquè falla la comanda? (explica-ho en menys de tres línies). Com ho puc arreglar?

4) Validació pràctica 3

El programa de la pràctica 3 (que reserva memòria per tal de comprovar que el swapfile fa la seva funció):

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define ONE_MB (1024 * 1024)

int main(void) {
    char *my_memory_pointer;

    while (true) {
        my_memory_pointer = malloc(ONE_MB);
        if (my_memory_pointer == NULL) {
            printf(stderr, "Memory allocation failed \n");
        }
    }
    return 0;
}

No funciona, no entenc perquè no s’està emplemenant la swap. Com ho arreglaries?

5) Un procés està abarcant massa CPU, quina comanda puc emprar per a que deixi d’executar-se?

6) Quines comandes executaries per tal d’habilitar un servei de sistema? I per arrancar-lo directament?

Dona per suposat que el teu sistema utilitza d’init system systemd