When the WordPress Install button is pressed (including the custom install option) in Application Vault, a progress bar is shown but never changes from 0%.

Log into Plesk.

Click "Tools and Utilities" > "Application Vault" > "My Apps".

Try installing the app. Here, the notification bar shows: Please wait…. 0%. This bar may remain the same for several hours with nothing happening.

Cause

A large number of applications are stuck in the psa.longtasks table. Or MySQL service is down.

Resolution

Backup the psa database by following the instructions in KB #213904125

Make sure that MySQL service is running:

Linux:

# service mysqld status 
# systemctl status mysqld.service 
# systemctl status mariadb

Windows:

> net start MySQL

Check that /dev/null has permissions crw-rw-rw-:
Linux:

 ls -la /dev/null
crw-rw-rw-. 1 root root 1, 3 Jul 19 15:15 /dev/null

Log into MySQL and access the psa database:

Linux:

MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql -uadmin psa

Windows:

"%plesk_dir%"\\MySQL\\bin\\mysql.exe -uadmin -p psa -P8306

Check the long tasks that are present on the server:

mysql> select * from longtasks;

+----+--------------+---------+-------------+-----------------+----------------+----------------+-------------+---------------+---------------------+---------------------+-------+
| id | type         | context | status      | statusProcessed | progressStatus | progressParams | progressMax | progressValue | startTime           | finishTime          | pid   |
+----+--------------+---------+-------------+-----------------+----------------+----------------+-------------+---------------+---------------------+---------------------+-------+
|  1 | aps-download | NULL    | started     |               0 | queue          | NULL           |         100 |             0 | 2017-07-21 13:34:03 | 0000-00-00 00:00:00 |     0 |
|  2 | aps-cache    | NULL    | done        |               0 | done           | NULL           |         100 |           100 | 2017-07-21 13:35:56 | 2017-07-21 13:35:56 | 31908 |
|  3 | aps-cache    | NULL    | done        |               0 | done           | NULL           |         100 |           100 | 2017-07-21 13:36:23 | 2017-07-21 13:36:23 | 31973 |
|  4 | aps-download | NULL    | not_started |               0 | queue          | NULL           |         100 |             0 | 2017-07-21 13:48:42 | 0000-00-00 00:00:00 |     0 |
|  5 | aps-cache    | NULL    | done        |               0 | done           | NULL           |         100 |           100 | 2017-07-21 13:57:51 | 2017-07-21 13:57:51 |  4515 |
+----+--------------+---------+-------------+-----------------+----------------+----------------+-------------+---------------+---------------------+---------------------+-------+

Delete these tasks:

mysql> truncate longtasks;
mysql> truncate longtaskparams;

Make sure /etc/localtime file has 644 permissions:

# ls -la /etc/localtime

If not, set it:

# chmod 644 /etc/localtime

Try installing the application again.