SadServer Salt solution URL: https://sadservers.com/scenario/salta

After logging into a server - notice that port 8888 is used. Missing tool lsof, I install with "sudo apt install lsof" and review what process is using port 8888. Nginx was used so I stopped the process with "sudo systemctl stop nginx"

Inside of Dockerfile - found missing proper port 8888 (it was written 8880) and for CMD there was "serve.js" instead of "server.js" - a local file in the same directory.

When the fix was solved, the docker container is built with cmd: "sudo docker build -t sampleapp:v1 . "

running app with "sudo docker run -p 8888:8888 sampleapp:v1" and the task is done

Solution for Cape Town task from URL: https://sadservers.com/scenario/capetown

After logging into the server, there is no working nginx.

Examine details on why nginx does not work show me the first line containing ";". So I removed ";" from the nginx file and nginx does not yet work.

After examining the error log - I was able to see and spot file limits.

After viewing /proc/[pid]/limits - I spot this (Max open files 10)

I did check limits for user www-data, as well as other things (fs.file-max, others)

In the end - Maybe systemD has some limitations per process.

After reading the .service file from systemD

Add # on the start of the line, reload the system daemon, and restart nginx and it works!

For this task, it takes 30 min to solve

SadServer Manhattan - medium, url: https://sadservers.com/scenario/manhattan My first medium task and solution. When I log in - running just

sudo systemctl restart postgresql@14-main.service

The issue is in these lines: "no space left on device"

After running df -h, notice 100% usage for /opt/pgdata/ Removing files that do not need it at all - solved this issue.

Solution

Solution for Bucharest

Bucharest - url for task: https://sadservers.com/scenario/bucharest File edit:

If we run command:

PGPASSWORD=app1user psql -h 127.0.0.1 -d app1 -U app1user -c '\q'

We could see issue with access and file named "pg_hba.conf " If we open file, and we could see next lines:

host    all             all             all                     reject
host    all             all             all                     reject

If we dig manual for file - we could find that "reject" do that - reject any connection. So replacing with md5 word reject (use sudo for editing file and restarting services), and restart services with

sudo systemctl restart postgresql@13-main.service

Solution for: https://sadservers.com/scenario/santiago

We have 3 files, each contains word "Alice". To count how many there is lines with word Alice

grep Alice *.txt | wc -l

After that we could find file with only once with:

grep Alice *.txt | cut  -d ":" -f 1 | sort | uniq -c | sort -r

Solution for Saskatoon Command:

awk '{print $1}' access.log | sort | uniq -c | sort -r | head -20

With awk, we pickup first field from the line - that is IP address. Second command - make sort this lines so next one command uniq could easy count (that is -c) and sort -r will set reverse list from highest to lower counts of IPs

Count of IPs from access log

For the task https://sadservers.com/scenario/saint-john there is easy solution by usage of tool called lsof (short for list list open files) where man pages https://man7.org/linux/man-pages/man8/lsof.8.html gives details of usage. Take notice here: I use command kill -9, but in case of important tasks like email servers and similar where are data valuable please use kill -15

Solution in one picture:

I'm solving SadServers Challenges!

I've decided to dive into the world of SadServers challenges (https://sadservers.com/scenarios)! This platform offers a variety of system administrator scenarios that test your troubleshooting skills and Linux knowledge.

With over 26 years of experience, I've encountered a wide range of Linux issues, including the infamous "Out of Memory" (OOM) problems with drivers.

Here's the exciting part:

I'll be tackling these challenges and sharing my solutions right here! The first one will be published today, June 7th, 2024, and I'll keep this page updated with links to all my future solutions.

Stay tuned for some in-depth troubleshooting and Linux problem-solving!

Easy

Saint John - Easy - solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-saint-john-task

Saskatoon - Easy solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-saskatoon

Santiago - Easy solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-santiago

Command line murderers - Easy solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-command-line-murderes

Taipei - Easy solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-taipei

Lhasa - Easy math solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-lhasa

Bucharest - Easy, Postgres solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-bucharest

Bilbao - Easy Kubernetes issue solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-biblao-k8s-task

Apia - Easy file tools usage solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-apia-task

Medium

Manhattan - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-manhattan-medium

Tokyio - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-tokyio-solution

Cape town - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-cape-town

Salta - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-salta-solution

Venice - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-venice

Oaxaca - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-oaxaca

Melbourn - medium, solution: https://www.vladimircicovic.com/2024/06/sadserver-solutions-melbourne