Install and Configure Fail2ban on Fedora/CentOS/RedHat

The following is a very basic guide for setting up Fail2ban for SSH.

Install and basic config

Install Fail2ban

sudo dnf install fail2ban

You may need to install the epel repo

sudo yum install epel-release

Configure to run on system boot

sudo systemctl enable fail2ban

Start Fail2ban service

sudo systemctl start fail2ban

Copy config file with

sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

Modify the config file

nano /etc/fail2ban/jail.local

Uncomment the following line and add any IPs that need to be whitelisted

ignoreip = 127.0.0.1/8 ::1 192.168.1.20

Save the file and restart Fail2Ban

sudo systemctl restart fail2ban

Configuring Fail2Ban for SSH

Create a new jail file in /etc/fail2ban/jail.d/ called sshd.local

nano /etc/fail2ban/fail.d/sshd.local

Add the following. Note: if you are using a custom ssh port, change “port = ssh” to “port = portnumber”

[sshd]
enabled = true
port = ssh
action = iptables-multiport
logpath = /var/log/secure
maxretry = 5
bantime = 300

Restart Fail2ban

sudo systemctl restart Fail2ban

You can list the firewall rules to verify that an IP gets banned.

iptables -S | grep ipaddress

Unbanning an IP Address

You can unban an IP address with the following command.

sudo fail2ban-client set sshd unbanip 192.168.1.100

You can check out the following link for more information

https://www.redhat.com/sysadmin/protect-systems-fail2ban

Fresh Install of Ubuntu Server Doesn’t use all Disk Space

For some reason Ubuntu server didn’t use all the available disk space while installing. Thankfully this is an easy fix.

sudo lvextend –resizefs -l +100%FREE ubuntu-vg/ubuntu-lv

If the Volume Group or LVM Volume is different, you will need to change the name in the above command. You can use the “sudo pvdisplay” and “sudo lvdisplay” to show you details about your volumes.

https://unix.stackexchange.com/questions/664486/lvm-root-partition-only-uses-half-the-volume-size

SFTP Server – Configure Folder to be used by two users

Bob is the companies local Linux administrator. He has been tasked with creating a secure shared SFTP folder so members in the R&D department can securely collaborate on “The New Project”.

Bob immediately recognizes a potential difficulty. If Steve and John are working on a prototype, how will John be able to edit Steve’s file if the user permissions are set to only allow John to read?

Bob first goes to the break room to locate a coffee mug.

After consulting Google and the man pages for sftp, sftp-server, sshd_config, sshd he found out what he needed to do.

  1. Create directory for the share
  2. Create a user group
  3. Create the individual users and add them to the user group
  4. Modify the sshd_config
  5. Restart the SSHD service and verify that it works

Create Directory for SFTP Share Directory

First Bob needed a directory to hold the R&D files.

mkdir /sftp/rdshare
mkdir /sftp/rdshare/files/
chown 755 /sftp/rdfiles

For some reason, he ran into issues with the folder getting set to the 775 permission which caused issues with logging in. Manually changing it to 755 fixed that issue.

Create User Group

Now Bob needs a user group to add everyone to.

sudo groupadd rdsftp

Now on to creating the users. Since we are just using the accounts for SFTP, we are setting the nologin option. None of these users will be able to use ssh to log on to the server.

sudo useradd -g rdsftp -s /sbin/nologin -M sftpadmin
passwd sftpadmin

Repeat for John, Steve, Jill, etc…

Use the sftpadmin user as an “admin” user and change the “home” directory permissions

chown -R adminuser:rdsftp /sftp/rdfiles

Modify sshd_config file

There are a couple things that need to be changed in the sshd_config file to make this all work.

sudo vi /etc/sshd_config

At the bottom of the file, Bob adds

# R&D SFTP share settings
Match Group rdsftp
        ChrootDirectory /sftp/rdshare/          # <- chroots the users into this directory
        ForceCommand internal-sftp -u 0002      # <- -u for umask.  Needed so users have write permissions for all files

This will chroot all the users into the /sftp/rdshare directory which makes /sftp/rdshare the users / directory.

The -u umask option is the secret for getting all the users to manage all the files. Without it, John would not be able to update Steve’s inventory file.

Restart services and test

Now we can restart the ssh server

sudo systemctl resart sshd

And verify that john can log in.

sftp john@localhost

Any existing sessions will need to be terminated for the changes to take effect.

Further reading.

https://askubuntu.com/questions/982123/multiple-owner-of-same-folder
https://www.tothenew.com/blog/how-to-set-up-shared-folderrepository-between-two-or-more-users-on-linux/
https://medium.com/linuxstories/linux-how-to-setup-an-sftp-server-37e6fb91649b
https://linuxandevops.wordpress.com/2017/07/30/ssh-scp-sftp-connections-and-file-permissions-part-2/

Add directory to path in Linux

Adding a directory to your path is really easy.

The following command adds the ~/script_folder to our PATH paths. Once run, we’ll be able to call any script in the script folder like it was a system utility.

PATH="$HOME/script_folder/:$PATH"

If you would like to always be able to call any file in your scripts folder, add the above command to your ~/.bashrc file.

You may need to restart your session for it to work.

Fix Peertube youtube-dl not Downloading

Issue was not being able to import a video into Peertube using a URL.

Peertube was set up to use youtube-dl which is in /var/www/peertube/storage/bin/youtube-dl. Further investigation showed that Peertube calls it with python.

For example

python youtube-dl video-to-download

Usually Python refers to Python 2 where as Python3 refers to Python 3.

We can create a symlink so that python = python3

sudo ln -s /usr/bin/python3 /usr/bin/python

This way when Peertube runs python, it technically will run it with python3.

Note you will probably run into issues if you do have Python 2 installed and need it. In my case, python was not installed and didn’t reference anything.

Enable Syslog for PowerDNS Recursor

  1. Enable Logging in PowerDNS Recursor Config
  2. Edit Systemd Unit File for PowerDNS to Allow Syslog
  3. Enable Logging in rsyslog Config File

The following links were helpful in setting things up.

https://doc.powerdns.com/recursor/running.html
https://www.reddit.com/r/linuxadmin/comments/9lc4jl/logging_queries_in_pdnsrecursor/

Enable logging in PowerDNS Recursor Config

First we need to find the line that says “disable-syslog” and uncomment/change it to

disable-syslog=no

Next find the line that says “quiet” and uncomment/change it to

quiet=no

Some other lines you may want to check and change

logging-facality=1
loglevel=6

Edit Systemd Unit File for PowerDNS to allow Syslog

Next we need to modify the Systemd unit file to allow PowerDNS Recursor to log to syslog.

systemctl edit --full pdns-recursor.service

On the ExecStart Line, remove the part that says

--disable-syslog

The resulting line should look something like

[Service]
ExecStart=/usr/sbin/pdns_recursor --socket-dir=%t/pdns-recursor --socket-dir=%t/pdns-recursor --daemon=no --write-pid=no --log-timestamp=no

Save the file.

Enable Logging in rsyslog Config File

Edit the rsyslog file

sudo vim /etc/rsyslog.conf

Add the following line

local1.*        /var/log/pdns_recursor.log

This should now log all of the PowerDNS Recursor log info to “/var/log/pdns_recursor.log”

Restart the rsyslog and PowerDNS Recursor service

sudo systemctl restart rsyslog
sudo systemctl restart pdns-recursor

You should now see DNS request in the log file.

tail /var/log/pdns_recursor.log

They should also show up in the “/var/log/messages”

How to Find Yesterdays Date in Linux

The wrong way to find yesterdays date:

I had a command that was used to see if. It used some arithmetic operators to subtract 1 from the current day. That would give us yesterdays day which we could then use to check if a backup was created then.

day=$(date +%d) ; date=$(($day - 1)) ; echo "yesterday date is $date"

It worked great, unless you happened to be on the 8th or 9th of the month. Looks like bash is interpreting 08 and 09 in octal format. https://stackoverflow.com/questions/24777597/value-too-great-for-base-error-token-is-08

-bash: 08: value too great for base (error token is "08")

The better way

Fortunately there is an easier and more reliable way to do this. Using the date command, you can specify yesterday and it will print out yesterdays date.

date --date=yesterday +%d

Much easier to use.

Some more info.

https://www.cyberciti.biz/tips/linux-unix-get-yesterdays-tomorrows-date.html?cf_chl_captcha_tk=N9iBfod_b0qUxjB2jIGlETgiZ.JXSxGpLmvQ83CzBvY-1636407896-0-gaNycGzNBmU

https://stackoverflow.com/questions/18180581/subtract-days-from-a-date-in-bash

Linux commands for CPU, RAM and GPU info

Some helpful commands for showing hardware information on Linux.

Show memory speed

sudo dmidecode --type 17

Show CPU Frequency in MHz

cat /proc/cpuinfo | grep MHz

Show a bunch of system info with inxi, may need to install it.

inxi 

Another cool program is screenfetch. Gives a nice overview of system specs

sudo dnf install screenfetch

and run with

screenfetch