Scenario: "Saint John": what is writing to this log file?
Level: Easy
Type: Fix
Access: Public
Description: A developer created a testing program that is continuously writing to a log file /var/log/bad.log and filling up disk. You can check for example with tail -f /var/log/bad.log. This program is no longer needed. Find it and terminate it. Do not delete the log file.
Test: The log file size doesn't change (within a time interval bigger than the rate of change of the log file).
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: There's a web server access log file at /home/admin/access.log. The file consists of one line per HTTP request, with the requester's IP address at the beginning of each line.
Find what's the IP address that has the most requests in this file (there's no tie; the IP is unique). Write the solution into a file /home/admin/highestip.txt. For example, if your solution is "1.2.3.4", you can do echo "1.2.3.4" > /home/admin/highestip.txt
Test: The SHA1 checksum of the IP address sha1sum /home/admin/highestip.txt is 6ef426c40652babc0d081d438b9f353709008e93 (just a way to verify the solution without giving it away.)
Scenario: "Resumable Server": Linux Upskill Challenge
Level: Easy
Type: Do
Access: Email
Description: This is a Debian 11 server without a challenge; it's for you to do as you please.
It's meant in principle for guided tutorials like the Linux Upskill Challenge, with some limitations (there's still no outgoing Internet access).
Once you are done with your task, you can stop (pause) your server from your dashboard.
From the dashboard at any time you can restart the stopped server to continue your tasks or you can stop the server if it's running. You can also destroy it at any time.
After 30 mins, the server will be stopped. You can restart it from the dashboard.
This is a "beta" feature and there can be some issues.
Description: There's a file /home/admin/scores.txt with two columns (the first number is a line number and the second one is a test score for example).
Find the average (more precisely; the arithmetic mean: sum of numbers divided by how many numbers are there) of the numbers in the second column (find the average score).
Use exactly two digits to the right of the decimal point. i. e., use exaclty two "decimal digits" without any rounding. Eg: if average = 21.349 , the solution is 21.34. If average = 33.1 , the solution is 33.10.
Save the solution in the /home/admin/solution file, for example: echo "123.45" > ~/solution
Tip: There's bc, Python3, Golang and sqlite3 installed in this VM.
Description: In a directory /home/admin/data, there are multiple files, all of them with same content. One of these files has been modified, a word was added. You need to identify which word it is and put it in the solution file (both newline terminated or not are accepted).
Test:md5sum /home/admin/solution should return 55aba155290288b58e9b778c8f616560 or 2eeefea9fc4b16ea624bed5c67a49d80
Check My Solution: The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can
Description: A spy has left a password in a file in /proc/sys . The contents of the file start with "secret:" (without the quotes).
Find the file and save the word after "secret:" to the file /home/admin/secret.txt with a newline at the end (e.g. if the file contents were "secret:password" do: echo "password" > /home/admin/secret.txt).
(Note there's no root/sudo access in this scenario).
Scenario: "Tokamachi": Troubleshooting a Named Pipe
Level: Easy
Type: Fix
Access: Email
Description: There's a process reading from the named pipe /home/admin/namedpipe.
If you run this command that writes to that pipe:
/bin/bash -c 'while true; do echo "this is a test message being sent to the pipe" > /home/admin/namedpipe; done' &
And check the reader log with tail -f reader.log
You'll see that after a minute or so it works for a while (the reader receives some messages) and then it stops working (no more received messages are printed to the reader log or it takes a long time to process one). Troubleshoot and fix (for example changing the writer command) so that the writer keeps sending the messages and the reader is able to read all of them.
Test: There should be a process running where a message is being sent to the pipe and that while that is running, another message can be sent to the pipe and read back. The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Scenario: "Yokohama": Linux Users Working Together
Level: Easy
Type: Fix
Access: Paid
Description: There are four Linux users working together in a project in this server: abe, betty, carlos, debora.
First, they have asked you as the sysadmin, to make it so each of these four users can read the project files of the other users in the /home/admin/shared directory, but none of them can modify a file that belongs to another user. Users should be able modify their own files.
Secondly, they have asked you to modify the file shared/ALL so that any of these four users can write more content to it, but previous (existing) content cannot be altered.
Test: All users (abe, betty, carlos, debora) can write to their own files. None of them can write to another user's file. All users can add more content (append)) to the shared/project_ALL file but none can change its current content. The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Scenario: "Rio de Janeiro": Do we have another option?
Level: Easy
Type: Fix
Access: Email
Description: This scenario server is dedicated to Jenkins, a Java application managed by systemd. Jenkins is failing to start. Troubleshoot and find the problem, then apply the solution so Jenkins runs properly.
Test: The service must return the string "Sign in - Jenkins" amongst some other html code. You can check with the command curl -s localhost:8888/login | grep Jenkins | head -n1
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: (NOTE: if you are a Pro user, you cannot SSH directly into this VM; click the "Open the Server Terminal" button to use the web browser instead).
SSH seems broken in this server. The user admin has an id_ed25519 SSH key pair in their ~/.ssh directory with the public key in ~/.ssh/authorized_keys but ssh 127.0.0.1 won't work.
Test: You can ssh locally, i.e. ssh admin@127.0.0.1 works.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: A critical health check script at /opt/scripts/health.sh is supposed to run every 10 seconds. This check is triggered by a systemd timer. The script's job is to check the local Nginx server and write its status (e.g., "STATUS: OK") to the log file at /var/log/health.log. The log file is not being updated, and it appears the health check is failing.
Find out why the health check system is broken and fix it. The check will pass once the /var/log/health.log file is being correctly updated by the timer with a STATUS: OK message.
Test: The /opt/scripts/health.sh script writes STATUS: OK to /var/log/health.log every 10 seconds.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: A critical backup cron job has silently stopped working 3 days ago. The backup script is located at /opt/backup/backup.sh and should create daily backups in /var/backups/daily/, but no new backups have been created recently.
Looking at the backup directory, you can see old backup files from a few days ago, proving the system used to work. However, there are no error emails, no obvious error logs, and the cron service appears to be running normally.
Fix ALL issues preventing the backups from running, so that backups are created successfully and reliably.
Test directory: /var/backups/daily/ Backup script: /opt/backup/backup.sh
Test: The solution will be validated by checking if a backup file has been created in the last 10 minutes.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Scenario: "Manhattan": can't write data into database.
Level: Medium
Type: Fix
Access: Public
Description: Your objective is to be able to insert a row in an existing Postgres database. The issue is not specific to Postgres and you don't need to know details about it (although it may help).
Helpful Postgres information: it's a service that listens to a port (:5432) and writes to disk in a data directory, the location of which is defined in the data_directory parameter of the configuration file /etc/postgresql/14/main/postgresql.conf. In our case Postgres is managed by systemd as a unit with name postgresql.
Description: There's an Nginx web server installed and managed by systemd. Running curl -I 127.0.0.1:80 returns curl: (7) Failed to connect to localhost port 80: Connection refused , fix it so when you curl you get the default Nginx page.
Test:curl -Is 127.0.0.1:80|head -1 returns HTTP/1.1 200 OK
Description: There is a Python WSGI web application file at /home/admin/wsgi.py , the purpose of which is to serve the string "Hello, world!". This file is served by a Gunicorn server which is fronted by an nginx server (both servers managed by systemd). So the flow of an HTTP request is: Web Client (curl) -> Nginx -> Gunicorn -> wsgi.py . The objective is to be able to curl the localhost (on default port :80) and get back "Hello, world!", using the current setup.
Test:curl -s http://localhost returns Hello, world! (serving the wsgi.py file via Gunicorn and Nginx)
Description: There's an etcd server running on https://localhost:2379 , get the value for the key "foo", ie etcdctl get foo or curl https://localhost:2379/v2/keys/foo
Description: A developer put an important password on his webserver localhost:5000 . However, he can't find a way to recover it. This scenario is easy to to once you realize the one "trick".
Find the password and save it in /home/admin/mysolution , for example: echo "somepassword" > ~/mysolution
Description: Find in the file frankestein.txt the second most frequent word and save in UPPER (capital) case in the /home/admin/mysolution file.
A word is a string of characters separated by space or newlines or punctuation symbols .,:; . Disregard case ('The', 'the' and 'THE' is the same word) and for simplification consider the apostrophe as another character not as punctuation ("it's" would be a word, distinct from "it" and "is"). Also disregard plurals ("car" and "cars" are different words) and other word variations (don't do "stemming").
We are providing a shorter test.txt file where the second most common word in upper case is "WORLD", so we could save this solution as: echo "WORLD" > /home/admin/mysolution
This problem can be done with a programming language (Python, Golang and sqlite3) or with common Linux utilities.
Description: You have been tasked with compressing the file /home/admin/names, which is 35147 bytes, to a size smaller than 9400 bytes. You can use any compressing tool at your disposal (there are many available in the server), also you can modify the file without deleting anything in it. Put the solution (compressed file) in the /home/user/admin/solution directory with the default extension used by the compression tool (example: ~/solution/names.gzip).
Test: The size of the compressed file is smaller than 9400 bytes.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
"Moyogalpa": Security Snag. The Trials of Mary and John
Scenario: "Moyogalpa": Security Snag. The Trials of Mary and John
Level: Medium
Type: Fix
Access: Email
Description: Mary and John are working on a Golang web application, and the security team has asked them to implement security measures. Unfortunately, they have broken the application, and it no longer functions. They need your help to fix it.
The fixed application should be able to allow clients to communicate with the application over HTTPS without ignoring any checks. (eg: curl https://webapp:7000/users.html) and serve its static files.
Test:curl https://webapp:7000/users.html should return the content of file.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: There is an nginx service running on port 443, it is the main web server for the company and looks like a new employee has deployed some changes to the configuration of supervisor and now it is not working as expected.
If you try to access curl -k https://bekasi it should return Hello SadServers! but for some reason it is not.
You cannot modify files from the /home/admin/bekasi folder in order to pass the check.sh
Description: (You can learn about Linux Libraries before starting this scenario).
The Linux shared library liblzma.so has been compromised (the real compromised XZ Utils liblzma has not been used). The liblzma.so at the path /usr/lib/x86_64-linux-gnu/liblzma.so.5.2.5 is the good one. Consider the same library liblzma.so.5.2.5 at other paths as compromised or malicious (ideally we would have used other real versions with different checksums).
Find all instances of this "malicious" liblzma library (remember, it's the same library but in different directory locations) and make it so none of the running processes use it, while the applications "webapp" and "jobapp" (both of which managed by systemd) still run properly (eg, stopping those applications is not a solution).
Test:lsof | grep liblzma.so.5 returns only the liblzma in the path: /usr/lib/x86_64-linux-gnu/liblzma.so.5.2.5
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: The Hanoi office has a Linux server with a large number of user accounts and groups. The system administrators need to identify which users belong to multiple groups for better access management.
Given two files, `users.txt` and `groups.txt`, create a new file `/home/admin/multi-group-users.txt` containing the usernames of users who belong to more than one group, one username per line, sorted alphabetically.
The `users.txt` file contains a list of usernames, one per line. The `groups.txt` file contains group names and their members, in the format `group_name:user1,user2,user3`.
There is a web server (Caddy) on HTTP port :80 but curl http://127.0.0.1 doesn't work. Find out what's wrong and make the necessary fixes so the web server returns a URL.
Note: as a limitation, the file /home/admin/db_connector.py must not be modified so that the challenge is considered solved properly. The web server has to respond on the IP address 127.0.0.1; not only on "localhost".
Test: The command curl http://127.0.0.1 returns a URL address.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: Given the file user_list.txt you must create all the users specified in the file with their corresponding passwords.
The entries in the user_list.txt file are stored as username;password
Test: All users are created with the right password. The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
The objective of this exercise is to delete all the Bash history lines that contain the term foo.
Clearing out or deleting the history file /home/admin/.bash_history is not allowed. Note that in our case, new commands (including the ones to try and delete "foo" from history) are also appended to the history file.
Test: Running history |grep "foo" returns nothing.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: A Python web application running on port 5000 from the /opt directory is experiencing severe performance issues; every request takes more than 5 seconds to complete. The application is supposed to use the redis-server cache service for speed.
Your mission is to diagnose the performance bottleneck and restore the application to its normal, fast response time.
Do not change the Python application file slow_app.py.
Test:curl localhost:5000 returns Data from FAST cache!
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: A developer has been working on Linux deployment scripts on their machine and then transferred the files to a Linux server. However, when they try to execute the scripts, they encounter the mysterious error:
-bash: cannot execute: required file not found
The scripts appear to be syntactically correct, but something is preventing them from executing properly. The developer needs your help to identify and fix the issue so the deployment can proceed.
There are several script files in /home/admin/deploy/ that need to be fixed before the deployment process can work correctly.
Test: All script files in /home/admin/deploy/ should execute without the cannot execute: required file not found error.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: A developer wants to run a program that splits their pile of their data into compressed parts for efficient transport across their network. Unfortunately when the tool runs it never completes.
The application binary in question is called bondo located in /home/admin/bondo.
Run it, then debug and help the developer find the issue.
Test: Executing /home/admin/bondo as admin returns part files generation completed!.
The file /etc/fstab has not been modified and the solution would work on reboot.
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
Description: Can't ping google.com. It returns ping: google.com: Name or service not known. Expected is being able to resolve the hostname. (Note: currently the VMs can't ping outside so there's no automated check for the solution).
Test:ping google.com should return something like PING google.com (172.217.2.46) 56(84) bytes of data.
Scenario: "Karakorum": WTFIT – What The Fun Is This?
Level: Hard
Type: Fix
Access: Paid
Description: There's a binary at /home/admin/wtfit that nobody knows how it works or what it does ("what the fun is this"). Someone remembers something about wtfit needing to communicate to a service in order to start. Run this wtfit program so it doesn't exit with an error, fixing or working around things that you need but are broken in this server. (Note that you can open more than one web "terminal").
Scenario: "Hong-Kong": can't write data into database.
Level: Hard
Type: Fix
Access: Paid
Description: (Similar to "Manhattan" scenario but harder). Your objective is to be able to insert a row in an existing Postgres database. The issue is not specific to Postgres and you don't need to know details about it (although it may help).
Postgres information: it's a service that listens to a port (:5432) and writes to disk in a data directory, the location of which is defined in the data_directory parameter of the configuration file /etc/postgresql/14/main/postgresql.conf. In our case Postgres is managed by systemd as a unit with name postgresql.
Description: A user client was added to the server, as well as their SSH public key. The objective is to be able to SSH locally (there's only one server) as this user client using their ssh keys. This is, if as root you change to this user sudo su; su client, you should be able to login with ssh: ssh localhost.
Test: As user admin: sudo -u client ssh client@localhost 'pwd' returns /home/client
Description: There is a web server on :5000 with a form. POSTing the correct form password into this web service will return a secret.
Save this secret provided by the web page (not the password you sent to it) to /home/admin/mysolution, for example: echo "SecretFromWebSite" > ~/mysolution
TIP: a developer worked on the web server code in this VM, using the same 'admin' account.
Scenario: "Zaragoza": Test changing critical files
Level: Hard
Type: Do
Access: Paid
Description: The goal is to make the script /home/admin/agent/check.sh return OK, without editing the original /etc/hosts file.
Think of testing changes in the critical directory /etc in a safe way. In this case, adding "127.0.0.1 my.local.test" to /etc/hosts .
There would be many ways of trying to do this with "sudo" access, like the usual procedure of making a copy of the config file, editing there and copying or renaming back to the original file. In our case, to avoid all those simple solutions, there is no general "sudo" privileges in this scenario (but there may be for some commands).
Test: The string my.local.test is in /etc/hosts
The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.
