Unit elasticsearch.service could not be found.

这个错误提示意味着您的系统中没有安装 Elasticsearch 服务单元。您需要安装 Elasticsearch 并创建一个服务单元才能启动和停止 Elasticsearch 服务。您可以按照 Elasticsearch 的官方文档或您使用的 Linux 发行版的文档进行安装和配置。安装完成后，您需要创建一个服务单元文件，例如 `/etc/systemd/system/elasticsearch.service`，并在其中定义 Elasticsearch 服务的配置和命令。然后使用 `systemctl start elasticsearch` 命令启动 Elasticsearch 服务。

相关问题

Unit iptables.service could not be found.

如果在 CentOS 系统中执行 `systemctl status iptables` 命令时出现 "Unit iptables.service could not be found." 的错误提示，这通常意味着你的系统使用的是 firewalld 而不是 iptables。

在 CentOS 7 和 CentOS 8 中，CentOS 默认使用的是 firewalld 作为防火墙管理工具。如果你想查看 firewalld 的状态，可以使用以下命令：

sudo systemctl status firewalld

该命令会显示 firewalld 的运行状态。如果 firewalld 已经启动，那么输出应该会类似这样：

● firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2021-09-21 17:50:10 UTC; 56min ago
     Docs: man:firewalld(1)
 Main PID: 1181 (firewalld)
   CGroup: /system.slice/firewalld.service
           └─1181 /usr/bin/python2 -Es /usr/sbin/firewalld --nofork --nopid

Sep 21 17:50:09 centos7 systemd[1]: Starting firewalld - dynamic firewall daemon...
Sep 21 17:50:10 centos7 systemd[1]: Started firewalld - dynamic firewall daemon.

如果 firewalld 没有启动，那么输出应该会显示如下信息：

● firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
   Active: inactive (dead)

如果你想查看更详细的 firewalld 配置，可以使用以下命令：

sudo firewall-cmd --list-all

该命令会输出详细的 firewalld 配置信息，包括各条规则的详细配置。

Failed to restart elasticsearch.service: Unit not found

As an AI language model, I don't have access to your specific system environment to provide a tailored solution. However, I can suggest some general troubleshooting steps:

1. Check if Elasticsearch is installed properly by running the command `sudo systemctl status elasticsearch.service`. If Elasticsearch is not installed, you can install it using the appropriate package manager for your operating system.

2. If Elasticsearch is installed, try restarting the service using the command `sudo systemctl restart elasticsearch.service`.

3. If the above command fails with the error "Unit not found", it could mean that the Elasticsearch service is not properly registered with the system. In this case, try re-registering the service using the command `sudo systemctl daemon-reload`.

4. If the above steps do not work, check the Elasticsearch logs for any error messages using the command `sudo journalctl -u elasticsearch.service`.

5. If you are still unable to restart the Elasticsearch service, seek help from the Elasticsearch community forums or consult a professional Elasticsearch administrator.