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0x05-processes_and_signals

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0x05. Processes and signals

DevOps Shell Bash Syscall Scripting

About Bash projects

Unless stated, all your projects will be auto-corrected with Ubuntu 20.04 LTS.

Resources

Read or watch:

man or help:

  • ps
  • pgrep
  • pkill
  • kill
  • exit
  • trap

Requirements

General

  • Allowed editors: vi, vim, emacs
  • All your files will be interpreted on Ubuntu 20.04 LTS
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project, is mandatory
  • All your Bash script files must be executable
  • Your Bash script must pass Shellcheck (version 0.7.0 via apt-get) without any error
  • The first line of all your Bash scripts should be exactly #!/usr/bin/env bash
  • The second line of all your Bash scripts should be a comment explaining what is the script doing

More Info

For those who want to know more and learn about all signals, check out this article.

Tasks

0. What is my PID

Write a Bash script that displays its own PID.

sylvain@ubuntu$ ./0-what-is-my-pid
4120
sylvain@ubuntu$

1. List your processes

Write a Bash script that displays a list of currently running processes.

Requirements:

  • Must show all processes, for all users, including those which might not have a TTY
  • Display in a user-oriented format
  • Show process hierarchy
sylvain@ubuntu$ ./1-list_your_processes | head -50
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         2  0.0  0.0      0     0 ?        S    Feb13   0:00 [kthreadd]
root         3  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [ksoftirqd/0]
root         4  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kworker/0:0]
root         5  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kworker/0:0H]
root         7  0.0  0.0      0     0 ?        S    Feb13   0:02  \_ [rcu_sched]
root         8  0.0  0.0      0     0 ?        S    Feb13   0:03  \_ [rcuos/0]
root         9  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [rcu_bh]
root        10  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [rcuob/0]
root        11  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [migration/0]
root        12  0.0  0.0      0     0 ?        S    Feb13   0:02  \_ [watchdog/0]
root        13  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [khelper]
root        14  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kdevtmpfs]
root        15  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [netns]
root        16  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [writeback]
root        17  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kintegrityd]
root        18  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [bioset]
root        19  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kworker/u3:0]
root        20  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kblockd]
root        21  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [ata_sff]
root        22  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [khubd]
root        23  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [md]
root        24  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [devfreq_wq]
root        25  0.0  0.0      0     0 ?        S    Feb13   0:41  \_ [kworker/0:1]
root        27  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [khungtaskd]
root        28  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kswapd0]
root        29  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [vmstat]
root        30  0.0  0.0      0     0 ?        SN   Feb13   0:00  \_ [ksmd]
root        31  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [fsnotify_mark]
root        32  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [ecryptfs-kthrea]
root        33  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [crypto]
root        45  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kthrotld]
root        46  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kworker/u2:1]
root        65  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [deferwq]
root        66  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [charger_manager]
root       108  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kpsmoused]
root       125  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [scsi_eh_0]
root       126  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kworker/u2:2]
root       172  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [jbd2/sda1-8]
root       173  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [ext4-rsv-conver]
root       409  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [iprt]
root       549  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [kworker/u3:1]
root       808  0.0  0.0      0     0 ?        S    Feb13   0:00  \_ [kauditd]
root       834  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [rpciod]
root       846  0.0  0.0      0     0 ?        S<   Feb13   0:00  \_ [nfsiod]
root         1  0.0  0.4  33608  2168 ?        Ss   Feb13   0:00 /sbin/init
root       373  0.0  0.0  19472   408 ?        S    Feb13   0:00 upstart-udev-bridge --daemon
root       378  0.0  0.2  49904  1088 ?        Ss   Feb13   0:00 /lib/systemd/systemd-udevd --daemon
root       518  0.0  0.1  23416   644 ?        Ss   Feb13   0:00 rpcbind
statd      547  0.0  0.1  21536   852 ?        Ss   Feb13   0:00 rpc.statd -L
sylvain@ubuntu$

2. Show your Bash PID

Using your previous exercise command, write a Bash script that displays lines containing the bash word, thus allowing you to easily get the PID of your Bash process.

Requirements:

  • You cannot use pgrep
  • The third line of your script must be # shellcheck disable=SC2009 (for more info about ignoring shellcheck error here)
sylvain@ubuntu$ sylvain@ubuntu$ ./2-show_your_bash_pid
sylvain   4404  0.0  0.7  21432  4000 pts/0    Ss   03:32   0:00          \_ -bash
sylvain   4477  0.0  0.2  11120  1352 pts/0    S+   03:40   0:00              \_ bash ./2-show_your_bash_PID
sylvain   4479  0.0  0.1  10460   912 pts/0    S+   03:40   0:00                  \_ grep bash
sylvain@ubuntu$

Here we can see that my Bash PID is 4404.

3. Show your Bash PID made easy

Write a Bash script that displays the PID, along with the process name, of processes whose name contain the word bash.

Requirements:

  • You cannot use ps
sylvain@ubuntu$ ./3-show_your_bash_pid_made_easy
4404 bash
4555 bash
sylvain@ubuntu$ ./3-show_your_bash_pid_made_easy
4404 bash
4557 bash
sylvain@ubuntu$

Here we can see that:

  • For the first iteration: bash PID is 4404 and that the 3-show_your_bash_pid_made_easy script PID is 4555
  • For the second iteration: bash PID is 4404 and that the 3-show_your_bash_pid_made_easy script PID is 4557

4. To infinity and beyond

Write a Bash script that displays To infinity and beyond indefinitely.

Requirements:

  • In between each iteration of the loop, add a sleep 2
sylvain@ubuntu$ ./4-to_infinity_and_beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
^C
sylvain@ubuntu$

Note that I ctrl+c (killed) the Bash script in the example.

5. Don't stop me now!

We stopped our 4-to_infinity_and_beyond process using ctrl+c in the previous task, there is actually another way to do this.

Write a Bash script that stops 4-to_infinity_and_beyond process.

Requirements:

  • You must use kill

Terminal #0

sylvain@ubuntu$ ./4-to_infinity_and_beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
Terminated
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ ./5-dont_stop_me_now 
sylvain@ubuntu$

I opened 2 terminals in this example, started by running my 4-to_infinity_and_beyond Bash script in terminal #0 and then moved on terminal #1 to run 5-dont_stop_me_now. We can then see in terminal #0 that my process has been terminated.

6. Stop me if you can

Write a Bash script that stops 4-to_infinity_and_beyond process.

Requirements:

  • You cannot use kill or killall

Terminal #0

sylvain@ubuntu$ ./4-to_infinity_and_beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
Terminated
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ ./6-stop_me_if_you_can
sylvain@ubuntu$

I opened 2 terminals in this example, started by running my 4-to_infinity_and_beyond Bash script in terminal #0 and then moved on terminal #1 to run 6-stop_me_if_you_can. We can then see in terminal #0 that my process has been terminated.

7. Highlander

Write a Bash script that displays:

  • To infinity and beyond indefinitely
  • With a sleep 2 in between each iteration
  • I am invincible!!! when receiving a SIGTERM signal

Make a copy of your 6-stop_me_if_you_can script, name it 67-stop_me_if_you_can, that kills the 7-highlander process instead of the 4-to_infinity_and_beyond one.

Terminal #0

sylvain@ubuntu$ ./7-highlander
To infinity and beyond
To infinity and beyond
I am invincible!!!
To infinity and beyond
I am invincible!!!
To infinity and beyond
To infinity and beyond
To infinity and beyond
I am invincible!!!
To infinity and beyond
^C
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ ./67-stop_me_if_you_can 
sylvain@ubuntu$ ./67-stop_me_if_you_can
sylvain@ubuntu$ ./67-stop_me_if_you_can
sylvain@ubuntu$

I started 7-highlander in Terminal #0 and then run 67-stop_me_if_you_can in terminal #1, for every iteration we can see I am invincible!!! appearing in terminal #0.

8. Beheaded process

Write a Bash script that kills the process 7-highlander.

Terminal #0

sylvain@ubuntu$ ./7-highlander 
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
Killed
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ ./8-beheaded_process
sylvain@ubuntu$

I started 7-highlander in Terminal #0 and then run 8-beheaded_process in terminal #1 and we can see that the 7-highlander has been killed.

9. Process and PID file

Write a Bash script that:

  • Creates the file /var/run/myscript.pid containing its PID
  • Displays To infinity and beyond indefinitely
  • Displays I hate the kill command when receiving a SIGTERM signal
  • Displays Y U no love me?! when receiving a SIGINT signal
  • Deletes the file /var/run/myscript.pid and terminates itself when receiving a SIGQUIT or SIGTERM signal

4

sylvain@ubuntu$ sudo ./100-process_and_pid_file
To infinity and beyond
To infinity and beyond
^CY U no love me?!

Executing the 100-process_and_pid_file script and killing it with ctrl+c.

Terminal #0

sylvain@ubuntu$ sudo ./100-process_and_pid_file
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
To infinity and beyond
I hate the kill command
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ sudo pkill -f 100-process_and_pid_file
sylvain@ubuntu$

Starting 100-process_and_pid_file in the terminal #0 and then killing it in the terminal #1.

10. Manage my process

37975393ead381f4d27f268f7337c6d3013b4991

Read:

man: sudo

Programs that are detached from the terminal and running in the background are called daemons or processes, need to be managed. The general minimum set of instructions is: start, restart and stop. The most popular way of doing so on Unix system is to use the init scripts.

Write a manage_my_process Bash script that:

  • Indefinitely writes I am alive! to the file /tmp/my_process
  • In between every I am alive! message, the program should pause for 2 seconds

Write Bash (init) script 101-manage_my_process that manages manage_my_process. (both files need to be pushed to git)

Requirements:

  • When passing the argument start:
    • Starts manage_my_process
    • Creates a file containing its PID in /var/run/my_process.pid
    • Displays manage_my_process started
  • When passing the argument stop:
    • Stops manage_my_process
    • Deletes the file /var/run/my_process.pid
    • Displays manage_my_process stopped
  • When passing the argument restart:
    • Stops manage_my_process
    • Deletes the file /var/run/my_process.pid
    • Starts manage_my_process
    • Creates a file containing its PID in /var/run/my_process.pid
    • Displays manage_my_process restarted
  • Displays Usage: manage_my_process {start|stop|restart} if any other argument or no argument is passed

Note that this init script is far from being perfect (but good enough for the sake of manipulating process and PID file), for example we do not handle the case where we check if a process is already running when doing ./101-manage_my_process start, in our case it will simply create a new process instead of saying that it is already started.

sylvain@ubuntu$ sudo ./101-manage_my_process
Usage: manage_my_process {start|stop|restart}
sylvain@ubuntu$ sudo ./101-manage_my_process start
manage_my_process started
sylvain@ubuntu$ tail -f -n0 /tmp/my_process 
I am alive!
I am alive!
I am alive!
I am alive!
^C
sylvain@ubuntu$ sudo ./101-manage_my_process stop
manage_my_process stopped
sylvain@ubuntu$ cat /var/run/my_process.pid 
cat: /var/run/my_process.pid: No such file or directory
sylvain@ubuntu$ tail -f -n0 /tmp/my_process 
^C
sylvain@ubuntu$ sudo ./101-manage_my_process start
manage_my_process started
sylvain@ubuntu$ cat /var/run/my_process.pid 
11864
sylvain@ubuntu$ sudo ./101-manage_my_process restart
manage_my_process restarted
sylvain@ubuntu$ cat /var/run/my_process.pid 
11918
sylvain@ubuntu$ tail -f -n0 /tmp/my_process 
I am alive!
I am alive!
I am alive!
^C
sylvain@ubuntu$

11. Zombie

C6mO7b3

Read what a zombie process is.

Write a C program that creates 5 zombie processes.

Requirements:

  • For every zombie process created, it displays Zombie process created, PID: ZOMBIE_PID
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • When your code is done creating the parent process and the zombies, use the function bellow
int infinite_while(void)
{
    while (1)
    {
        sleep(1);
    }
    return (0);
}

Example:

Terminal #0

sylvain@ubuntu$ gcc 102-zombie.c -o zombie
sylvain@ubuntu$ ./zombie 
Zombie process created, PID: 13527
Zombie process created, PID: 13528
Zombie process created, PID: 13529
Zombie process created, PID: 13530
Zombie process created, PID: 13531
^C
sylvain@ubuntu$

Terminal #1

sylvain@ubuntu$ ps aux | grep -e 'Z+.*<defunct>'
sylvain  13527  0.0  0.0      0     0 pts/0    Z+   01:19   0:00 [zombie] <defunct>
sylvain  13528  0.0  0.0      0     0 pts/0    Z+   01:19   0:00 [zombie] <defunct>
sylvain  13529  0.0  0.0      0     0 pts/0    Z+   01:19   0:00 [zombie] <defunct>
sylvain  13530  0.0  0.0      0     0 pts/0    Z+   01:19   0:00 [zombie] <defunct>
sylvain  13531  0.0  0.0      0     0 pts/0    Z+   01:19   0:00 [zombie] <defunct>
sylvain  13533  0.0  0.1  10460   964 pts/2    S+   01:19   0:00 grep --color=auto -e Z+.*<defunct>
sylvain@ubuntu$

In Terminal #0, I start by compiling 102-zombie.c and executing zombie which creates 5 zombie processes. In Terminal #1, I display the list of processes and look for lines containing Z+.*<defunct> which catches zombie process.