os: centos 7.6.1810
es: elasticsearch Version 7.12.0 (Build 778cc7261dfdd1)
使用 rpm 方式安装的 elasticsearch ()

# ls -l 
-rw-r--r--  1 root root 327593346 Apr 15 13:18 elasticsearch-7.12.0-x86_64.rpm

# cat /usr/lib/systemd/system/elasticsearch.service

[Unit]
Description=Elasticsearch
Documentation=https://www.elastic.co
Wants=network-online.target
After=network-online.target

[Service]
Type=notify
RuntimeDirectory=elasticsearch
PrivateTmp=true
Environment=ES_HOME=/usr/share/elasticsearch
Environment=ES_PATH_CONF=/etc/elasticsearch
Environment=PID_DIR=/var/run/elasticsearch
Environment=ES_SD_NOTIFY=true
EnvironmentFile=-/etc/sysconfig/elasticsearch

WorkingDirectory=/usr/share/elasticsearch

User=elasticsearch
Group=elasticsearch

ExecStart=/usr/share/elasticsearch/bin/systemd-entrypoint -p ${PID_DIR}/elasticsearch.pid --quiet

# StandardOutput is configured to redirect to journalctl since
# some error messages may be logged in standard output before
# elasticsearch logging system is initialized. Elasticsearch
# stores its logs in /var/log/elasticsearch and does not use
# journalctl by default. If you also want to enable journalctl
# logging, you can simply remove the "quiet" option from ExecStart.
StandardOutput=journal
StandardError=inherit

# Specifies the maximum file descriptor number that can be opened by this process
LimitNOFILE=65535

# Specifies the maximum number of processes
LimitNPROC=4096

# Specifies the maximum size of virtual memory
LimitAS=infinity

# Specifies the maximum file size
LimitFSIZE=infinity

# Disable timeout logic and wait until process is stopped
TimeoutStopSec=0

# SIGTERM signal is used to stop the Java process
KillSignal=SIGTERM

# Send the signal only to the JVM rather than its control group
KillMode=process

# Java process is never killed
SendSIGKILL=no

# When a JVM receives a SIGTERM signal it exits with code 143
SuccessExitStatus=143

# Allow a slow startup before the systemd notifier module kicks in to extend the timeout
TimeoutStartSec=75

[Install]
WantedBy=multi-user.target

# Built for packages-7.12.0 (packages)