SSL Issue: Regenerate Certificate Revocation List

Currently, there is a known issue of a socket leak, causing SSL to stop working after a period of time. Even restarting the server OS would not help, documented under: https://github.com/FreeTAKTeam/FreeTakServer/issues/368

The cause is that Certificate Revocation List (CRL) is expired. A Certificate Revocation List (CRL) is a type of security feature used in public key infrastructure (PKI) systems. It is a list of digital certificates that have been revoked by the certificate authority (CA) before their scheduled expiration date. This list contains information about the certificate serial numbers, the revocation dates, and the reason for revocation. Since FTS version 1.9, when you delete a user that has a certificate, the certificate will be revoked. We have now created a script that will fix the issue re-creating the CRL.

Please follow the steps below. Note that if you are trying to use this with 2.x.y the next step is not necessary:

Install DigitalPy>=0.3.9.1 (the version where CRL regeneration support was added) with the following command:
```
pip install DigitalPy>=0.3.9.1
```

Now execute the CRL-Regen utility. The location of the certs would under /path/to/fts/certs/ca.pem typically would be /opt/fts/certs:

 python3 -m digitalpy.core.security.crl_regen --ca-pem-path /opt/fts/certs/ca.pem --ca-key-path /opt/fts/certs/ca.key --crl-path /opt/fts/certs/FTS_CRL.json

Now stop FTS:

 sudo systemctl stop fts && sudo pkill python

Finally, restart your system for good measure (not required but recommended to ensure CRL updates are applied)
```
sudo reboot -n
```

note: the FTS certs directory can generally be found at

/usr/local/lib/python{{ python_version }}/dist-packages/FreeTAKServer/certs

SSL issue: Change the Number of max file open

If you have an issue with SSL probably depends on a limited amount of socket files you can open on the machine. in a console type

ulimit -n

If you get 1024 or less you will need to increase the allowed file descriptors for the user.

The procedure on Ubuntu 20.04 and 22.04 is this:

sudo sed -i 's/DefaultLimitNOFILE=1024/DefaultLimitNOFILE=1048576 /g' /etc/systemd/system.conf

grep NOFILE /etc/systemd/system.conf DefaultLimitNOFILE=1048576

or open the file with an editor

vi /etc/systemd/system.conf

open the file with an editor and edit line 61 Uncomment DefaultLimitNOFILE and set your limit there, e.

Restart with:

shutdown -r 0

Then, check the user file descriptor limit again:

ulimit -n

Before:

ulimit -n
ulimit -Sn
ulimit -Hn

1024
1024
1024

After:

ulimit -n
ulimit -Sn
ulimit -Hn

1048576
1048576
1048576

The limits can be controlled by systemd and this is what we do here — instruct systemd to set it to 100k. Note that this setting will apply to all users

by increasing the soft limit for no file here /etc/security/limits.conf

you should be able to increase this time, try 20000 and in theory the time should multiply 20x. so, you should be able to run for about 40 hours uninterrupted the file may also be under the path /etc/limits.conf also add this line:

fs.file-max = 65536

to this file: /etc/sysctl.conf then restart and check file limits with this

ulimit -Sn