Plesk is inaccessible after executing “apt-get install npm”: 99 directory index of “/opt/psa/admin/htdocs/” is forbidden

Symptoms

1. Plesk is inaccessible with one of the following errors after executing
apt install npm
command:

   403 Forbidden

   404 not found by nginx

2. Plesk packages were removed, according to /var/log/apt/history.log:

   Commandline: apt install npm 
   Install: fakeroot:amd64 (1.20-3ubuntu2, automatic), node-npmlog:amd64 (0.0.4-1, automatic), node-node-uuid:amd64 (1.4.0-1, automatic).....
   .....
   Remove: plesk-service-node-utilities:amd64 (12.5.30-ubuntu14.04.build1205150826.19), psa-updates:amd64 (12.5.28-ubuntu14.04.build1205150720.14), plesk-dovecot:amd64 (2.2.18-ubuntu14.04.15081914), psa-health-monitor:amd64 (12.5.30-ubuntu14.04.build1205150819.14), psa-drweb-configurator:amd64 (12.5.30-ubuntu14.04.build1205150826.19), psa-spamassassin:amd64 (12.5.30-ubuntu14.04.build1205150826.19), plesk-mail-pc-driver:amd64 (12.5.30-ubuntu14.04.build1205161215.16), plesk-dovecot-imap-driver:amd64 (12.5.30-ubuntu14.04.build1205150826.19), psa-locale-base-en-us:amd64 (12.5.30-ubuntu14.04.build1205160722.12), psa-mnemo:amd64 (4.2.6-ubuntu14.04.build1205150819.14), psa-zendframework:amd64 (1.11.15-ubuntu14.04.build1205161215.18), psa-turba:amd64 (4.2.7-ubuntu14.04.build1205150819.14), plesk-web-hosting:amd64 (12.5.30-ubuntu14.04.build1205150826.19), plesk-core:amd64 (12.5.30-ubuntu14.04.build1205150826.19)

3. Errors in /var/log/plesk/sw-cp-server/error.log when trying to open Plesk login page:

   [error] 1795#0: *99 directory index of "/opt/psa/admin/htdocs/" is forbidden,
   [error] 1795#0: *99 open() "/opt/psa/admin/htdocs/error_docs/403.html" failed (2: No such file or directory)

   OR

   [error] 1795#0: *99 open() "/opt/psa/admin/htdocs/error_docs/403.html" failed (2: No such file or directory), client: 203.0.113.111, server: , request: "GET / HTTP/1.1", host: "203.0.113.2:8443"

Cause

Plesk packages were removed due to npm dependencies conflicts. To avoid this issue in future, “apt install npm” should not be executed on the server. Plesk has it’s own npm and to manage node.js modules use Plesk UI.

Resolution

1. Connect to Plesk server via SSH.

2. Download Plesk Installer from Plesk website and launch it:

   # wget https://autoinstall.plesk.com/plesk-installer
   # chmod +x plesk-installer
   # ./plesk-installer

3. On the Main components list for Plesk screen select Plesk and proceed with the installation.

4. Check in the /var/log/apt/history.log file what other packages were deleted and install corresponding components using Plesk Installer:

   # plesk installer