One of the following symptoms is true for webmail:
Unable to log into Roundcube webmail with correct credentials:
Connection to storage server failed
Webmail is not accessible with the error message:
PLESK_INFO: Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at [email protected] to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.
Children of different processes are killed with signal 9. The corresponding message appears in
server spamd: spamd: handled cleanup of child pid  due to SIGCHLD: KILLED, signal 9 (0009)
server dovecot: service=pop3, [email protected] ip=[203.0.113.2]. Fatal: master: service(pop3): child 32379 killed with signal 9
Plesk or Plesk extensions do not work.
The following error messages appear in
kernel: PAX: terminating task: /opt/plesk/php/7.3/bin/php-cgi(php-cgi):20401, uid/euid: 994/994, PC: 000003337a7ed010, SP: 0000039fadcfccd8
kernel: grsec: denied resource overstep by requesting 4096 for RLIMIT_CORE against limit 0 for /opt/plesk/php/7.3/bin/php-cgi[php-cgi:20401] uid/euid:994/994 gid/egid:1006/1006, parent /usr/sbin/httpd[/usr/sbin/httpd:27947] uid/euid:0/48 gid/egid:48/48
Error: denied RWX mmap of <;anonymous mapping>; by /usr/local/psa/admin/sbin/modules/panel-migrator/plesk-migrator[plesk-migrator:25177] uid/euid:0/0 gid/egid:0/1001, parent /usr/bin/sw-engine[sw-engine:25164] uid/euid:0/0 gid/egid:0/0
Grsecurity system is blocking Plesk executable files.
Grsecurity is not supported by Plesk.
As a workaround, add the binary from the error message to exclusions of PAX monitoring. In this example, PHP 7.3 is added to the exclusions:
# paxctl -cm /opt/plesk/php/7.3/bin/php-cgi