Most likely not related but your OS is EOL since 2021 
Hello bt90/All,
I’ve carried out the purge and clean, but now things have taken a step further back in that I’m unable to (re) install the application. 
sudo apt-get update
Hit:1 http://ppa.launchpad.net/utappia/stable/ubuntu xenial InRelease
Hit:2 https://linux.teamviewer.com/deb stable InRelease
Hit:3 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:4 http://archive.canonical.com/ubuntu xenial InRelease
Hit:5 http://archive.ubuntu.com/ubuntu xenial InRelease
Ign:6 http://packages.linuxmint.com sylvia InRelease
Hit:7 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:9 http://packages.linuxmint.com sylvia Release
Hit:10 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Err:8 https://apt.syncthing.net syncthing InRelease
The following signatures were invalid: NODATA 3 NODATA 1 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D26E6ED000654A3E
Reading package lists... Done
E: GPG error: https://apt.syncthing.net syncthing InRelease: The following signatures were invalid: NODATA 3 NODATA 1 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D26E6ED000654A3E
sudo apt-get install syncthing
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package syncthing
Honestly, I’d start with an OS upgrade and deal with the Syncthing repo issue after that. There’s a chance that this problem will resolve itself along the way.
Hi bt90,
That’s what’s going through my head too.
The Proliant box I use is also a bit ‘long in the tooth’ now, ML10 Gen 9, but I think I’ll put the current Mint on it and see how it goes.
I have a terrible memory and remember that I ran into all sorts of issues with video display when I first set it up.
I’m going to go for broke and see how things pan out from fresh. 
Fingers crossed. 
I’ll report back …
Hello All,
I keep hearing … WILMA!! and then cue the Flintstones intro music!
So I have blown away my server and loaded Mint 22/Wilma Cinnamon desktop on it.
I cannot believe how much faster it is! I have also lost all the screen tearing issues and inability to parse audio when I remotely connect to it.
Amazing! 
Syncthing is installed and the daemon started. No more repository errors and the only issue is that, for some reason, it will not let me see 127.0.0.1:8384.
I’m putting it aside for now, but will get back on the case tomorrow abw.
Thanks again!
Robin.
Yabba Dabba Doo! 
Welcome to 2024! 
A whole lot of changes since 2017 – Linux kernel 4.10 → 6.8, GTK 3 → 4 … the list goes on and on.
Ha Ha! Yes, indeed. Where does the time go?
Not always the best mantra, “if it ain’t broke, don’t try and fix it” 
Sorted the GUI and set-up the first sync.
Must definitely give it a break now!
Thanks everyone for your assistance.
Take care, Robin.
It won’t matter anymore now. But this error message might be a clue for others seeing similar symptoms in the future. I think you might have copied an extra quote character there into the APT sources list. That would explain failure when updating and why no actual sources for the package showed up in the policy listing.
Glad it’s working for you now. Take care!
Hello André,
You’re absolutely right. I try to get things like that 100%, but occasionally miss something. 
‘Careless’ was a word that often featured on my school report card!
Fortunately, the articles I write and edit - as a radio ham - are proof read by others before going out!
Have a great Christmas,
Robin.
At this point it’s just academic, but thought it might be helpful for others who encounter a similar issue.
After installing Linux Mint 18.3 (aka. “Sylvia”) that was released in 2017 and the older Syncthing keyring, a snippet from gpg --list-packets syncthing-archive-keyring.gpg:
:signature packet: algo 1, keyid D26E6ED000654A3E
version 4, created 1419843039, md5len 0, sigclass 0x13
digest algo 2, begin of digest 5e bb
The older Syncthing keyring from 2014-12-29 used SHA-1 for its digest algorithm (indicated by the “algo 2” according to IANA).
However, beginning with APT 1.2.7, SHA1-based signatures were deprecated – Linux Mint 18.3 ships with APT 1.2.24, so the older Syncthing key isn’t compatible.
After adding apt.syncthing.net to the list of repos along with the latest Syncthing keyring with key ID E5665F9BD5970C47, the relevant portion of the output from apt update -o Debug::Acquire::gpgv=true:
0% [Working]inside VerifyGetSigners
0% [11 InRelease gpgv 15.7 kB]Preparing to exec: /usr/bin/apt-key --quiet --readonly --keyring /usr/share/keyrings/syncthing-archive-keyring.gpg verify --status-fd 3 /tmp/apt.sig.Q5mtmK /tmp/apt.data.1k13Vg
Read: [GNUPG:] NODATA 3
Got NODATA!
Read: [GNUPG:] SIG_ID Iboey1SeVitxN0zcfZSbJ41SnA4 2024-12-06 1733448940
Read: [GNUPG:] GOODSIG E5665F9BD5970C47 Syncthing Release Management <release@syncthing.net>
Got GOODSIG, key ID: E5665F9BD5970C47
Read: [GNUPG:] NOTATION_NAME salt@notations.openpgpjs.org
Read: [GNUPG:] NOTATION_DATA [%20not%20human%20readable%20]
Read: [GNUPG:] VALIDSIG FBA2E162F2F44657B38F0309E5665F9BD5970C47 2024-12-06 1733448940 0 4 0 1 8 01 FBA2E162F2F44657B38F0309E5665F9BD5970C47
Got trusted VALIDSIG, key ID: FBA2E162F2F44657B38F0309E5665F9BD5970C47
Read: [GNUPG:] ERRSIG D26E6ED000654A3E 1 8 01 1733448940 9
Got ERRSIG
Read: [GNUPG:] NO_PUBKEY D26E6ED000654A3E
Got NO_PUBKEY
Read: [GNUPG:] NODATA 1
Got NODATA!
gpgv exited with status 2
Summary:
Good: GOODSIG E5665F9BD5970C47,
Bad: NODATA 3
, NODATA 1
,
Worthless:
SoonWorthless:
NoPubKey: NO_PUBKEY D26E6ED000654A3E
,
Err:11 https://apt.syncthing.net syncthing InRelease
The following signatures were invalid: NODATA 3 NODATA 1 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D26E6ED000654A3E
Reading package lists... Done
E: The repository 'cdrom://Linux Mint 18.3 _Sylvia_ - Release amd64 20171213 xenial Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: GPG error: https://apt.syncthing.net syncthing InRelease: The following signatures were invalid: NODATA 3 NODATA 1 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D26E6ED000654A3E
The output above provides more context to the vague The following signatures were invalid NODATA 3 NODATA1 error from just issuing apt update.
apt-key stumbles while following the chain of trust, so Linux Mint 18.3 also can’t use Syncthing’s newest keyring.
So definitely a lot easier and cleaner to upgrade to a more recent OS version if relying on the system package manager, otherwise setting up Syncthing to auto-upgrade might be the next best option if an OS upgrade isn’t feasible yet.
2 Likes
Hello gadget,
Thanks for your debugging of the keyring isue. I don’t follow all that I read, but the gist of it makes sense and, as you say, it will hopefully assist any other 'stick in the mud’s like myself! 
Now I’m battling MS’s security challenges with Win10/11 and not being able to see Mint 22 shares. Ho Hum! 
I’m thinking EXT4 wasn’t such a good choice for a machine that I want to share with Win devices.
Take care,
Robin.
You’re welcome.
Using ext4 for the receiving end is fine, just be sure to enable “Ignore Permissions” for the Syncthing folder settings because there’s little that Linux and Windows filesystems share in common in terms of permissions.
And depending on particular situation, modTimeWindowS Syncthing config option might be helpful.
Thanks. 