because wildfly sometimes stops for unknown reasons on cntos7,

I checked the log shown that mongo connection record might be a reason,

after some searching of documentation,

this is how to make ulimits setting works as following.

step 1:

if you wish to modify the system services, go to /usr/lib/systemd/system,

find your service, for example, mongod.service

modify that file, under the [service] tag,

adding lines include:

# open files
LimitNOFILE=32000
# processes/threads
LimitNPROC=32000

step 2:

systemctl daemon-reload && systemctl restart mongod

then the change of ulimits took effect.

if you wish to modify some process other than system services, like wildfly

make a new file under /etc/security/limits.d/

named a file after that process, like 100-wildfly.conf, the number shown in front of a file indicated its group numeratically,

adding lines below:

wildfly soft nproc 32000
wildfly hard nproc 32000
wildfly soft nofile 32000
wildfly hard nofile 32000

then restart your process to take effect on that modification.

notice: you can enlarge the number over examples above, maybe for 64000, if your system has more physical memories to work with it.