Composer Manager: Composer’s install command must be run

1.0 Error

After updating the Drupal 7 version in a website, the following error was observed in the configuration of the Composer Manager module.

Composer Manager: Composer's install command must be run to generate the autoloader and install the required packages.

The above message was followed by the status of packages managed by the Composer. At the end, there was a button to Rebuild composer.json file.

2.0 Resolution

The problem was resolved with the following steps.

The button Rebuild composer.json file was clicked to rebuild the composer.json file. The message A composer.json file was written to <webroot>/sites/default/files/composer was printed. The following commands were given.

$ sudo apt-get install composer
$ cd <webroot>/sites/default/files/composer
$ ls -ls
total 24
 4 -rw-rw-r-- 1 user1 www-data   260 Apr 30 14:58 composer.json
20 -rw-rw-r-- 1 user1 www-data 18925 Jun 20  2017 composer.lock
$ composer install