Solve the problem with solr_ulimit_checks

At one not-so-great moment, the search results for Solr on the eighth drupal ceased to be displayed. After going to the search api, I saw that the Solr server was not running. When trying to view the server status in ssh, using the command

sudo systemctl status solr

there was such a message

solr.service - LSB: Controls Apache Solr as a Service   Loaded: loaded (/etc/rc.d/init.d/solr; bad; vendor preset: disabled)   Active: failed (Result: exit-code) since Mon 2021-03-29 16:34:32 MSK; 6min ago     Docs: man:systemd-sysv-generator(8)  Process: 901 ExecStart=/etc/rc.d/init.d/solr start (code=exited, status=1/FAILURE)Mar 29 16:34:30 294207-bd.tmweb.ru su[905]: (to solr) root on noneMar 29 16:34:32 294207-bd.tmweb.ru solr[901]: *** [WARN] ***  Your Max Processes Limit is currently 4096.Mar 29 16:34:32 294207-bd.tmweb.ru solr[901]: It should be set to 65000 to avoid operational disruption.Mar 29 16:34:32 294207-bd.tmweb.ru solr[901]: If you no longer wish to see this warning, set SOLR_ULIMIT_CHECKS to false in your profile or solr.in.shMar 29 16:34:32 294207-bd.tmweb.ru solr[901]: Port 8983 is already being used by another process (pid: 1166)Mar 29 16:34:32 294207-bd.tmweb.ru solr[901]: Please choose a different port using the -p option.Mar 29 16:34:32 294207-bd.tmweb.ru systemd[1]: solr.service: control process exited, code=exited status=1Mar 29 16:34:32 294207-bd.tmweb.ru systemd[1]: Failed to start LSB: Controls Apache Solr as a Service.Mar 29 16:34:32 294207-bd.tmweb.ru systemd[1]: Unit solr.service entered failed state.Mar 29 16:34:32 294207-bd.tmweb.ru systemd[1]: solr.service failed.

Having started googling, I found a similar problem with solr limits, which, according to the help, should have been solved by the command

ulimit -a

which did not help in my case.

This option helped:

Find the config file /etc/systemd/system.conf, which will contain a bunch of commented out lines. Find these two lines

#DefaultLimitNOFILE=#DefaultLimitNPROC=

Remove comments by removing # and set the value to 65000

DefaultLimitNOFILE=65000DefaultLimitNPROC=65000

After that, you can run solr with the command

sudo service solr start

In case it didn't pick it up right away, don't panic and restart

sudo service solr restart

After that, the search server in the search cpi of our Drupal should start successfully.