Category: Computing

How to Fix Missing Database Indexes Problem on NextCloudPi After Upgrade to Version 14.0.x

After upgrading an instance of NextCloudPi from version 13 to version 14, I received the following error notification:

The database is missing some indexes. Due to the fact that adding indexes on big tables could take some time they were not added automatically. By running "occ db:add-missing-indices" those missing indexes could be added manually while the instance keeps running. Once the indexes are added queries to those tables are usually much faster. ° Missing index "parent_index" in table "oc_share". ° Missing index "fs_mtime" in table "oc_filecache".

In short, the table “oc_share” was missing the index “parent_index” and the table “oc_filecache” was missing the index “fs_mtime”.

I tried SSH-ing to my NextCloudPi server and running the suggested command, “occ db:add-missing-indices” but it generated an error.

Despite the missing database entries, the instance still seemed to run fine, but I found the constant error message vexing.

After some online research and examination of my NextCloudPi instance’s directory structure, I found the following solution, and not seeing it posted elsewhere, thought I’d share it here:

1. SSH to your NextCloudPi instance.

2. Get a root prompt by entering:

sudo bash

3. Go up to the root directory by typing the following command twice (or as many times as necessary):

cd ../

4. Switch to the nextcloud directory:

cd /var/www/nextcloud

5. Run the following command:

sudo -u www-data php occ db:add-missing-indices

6. You should receive something like the following prompts (which I received):

Check indices of the share table.
Adding additional parent index to the share table, this can take some time...
Share table updated successfully.
Adding additional mtime index to the filecache table, this can take some time...
Filecache table updated successfully.

7. That’s all! Type “exit” and hit enter to terminate the SSH session. The error message should no longer appear.

How to Use Quad9 ( DNS Resolution with Algo VPN

Algo VPN is an open source project from computer security firm Trail of Bits. It facilitates the creation of a non-logging (and optionally ad-blocking) virtual private network (VPN) on a virtual private server (VPS). I’ve been using Algo VPN for a couple months and am pleased with it’s performance, particularly on Apple devices, which natively support the IKEv2 protocol implemented by Algo VPN.

By default, Algo VPN uses Google’s domain name resolution (DNS) servers ( and Recently, I heard about an alternative, non-profit DNS service called Quad9 ( that has some attractive features. In particular, Quad9 blocks known malicious domains, collects no personally-identifiable information, and does not store the IP addresses of end users to disk. Steve Gibson spoke about Quad9 in episode 638 of his weekly Security Now podcast.

Perhaps in the future, Algo VPN will offer Quad9 as an alternative to Google’s DNS servers. But until such time, and for already existing installations, here’s how you can point your Algo VPN server to Quad9’s DNS servers:

1. SSH to your Algo server via your terminal app:

ssh root@ip -i ~/.ssh/algo.pem

2. Open /etc/dnsmasq.conf for editing:

nano /etc/dnsmasq.conf

3. Find the lines:


4. Replace with (the second line, not originally included here, is Quad9’s secondary IPv4 address; thanks to commenter “c.” for noting this):


5. Hit Control-X to exit, choosing Y to save and keeping the same file name.

6. Type reboot at the command line to reboot.

That’s all! Your Algo VPN server will now use Quad9 for DNS resolution.

How to Upgrade to GnuPG 2.x on Ubuntu Linux

If you are using the Enigmail security add-on for Mozilla Thunderbird under Ubuntu Linux, you may have recently discovered (as I did today) that it no longer works with the version of GnuPG that you have installed, and that you need to upgrade. But it’s not evident how to do this, as there is no GnuPG update available in the Ubuntu Software Center.

Fortunately, there is an easy way to upgrade Ubuntu to GnuPG 2. Just open a terminal and type:

sudo apt-get install gnupg2

and enter your password when prompted.

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