systemd: add introduction for systemd file open limit

systemd/README.md

@@ -1,27 +1,72 @@
 ## Service
 
-binary file:
+### Install
+
+#### 1. copy binary file
+
 ```bash
 cp glider /usr/bin/
 ```
 
-service file:
+#### 2. add service file
+
 ```bash
 # copy service file to systemd
 cp systemd/glider@.service /etc/systemd/system/
 ```
 
-config file: ***server***.conf
+#### 3. add config file: ***server***.conf
+
 ```bash
 # copy config file to /etc/glider/
 mkdir /etc/glider/
 cp ./config/glider.conf.example /etc/glider/server.conf
 ```
 
-enable and start service: glider@***server***
+#### 4. enable and start service: glider@***server***
+
 ```bash
 # enable and start service
 systemctl enable glider@server
 systemctl start glider@server
 ```
+
 See [glider@.service](glider%40.service)
+
+### Open file limit
+
+#### 1. setup system limit
+
+vim /etc/security/limits.d/unlimited.conf
+
+```bash
+* soft nofile unlimited
+* hard nofile unlimited
+* soft nproc unlimited
+* hard nproc unlimited
+```
+
+#### 2. change **systemd** limit
+
+```bash
+echo DefaultLimitNOFILE=102400 >> /etc/systemd/system.conf
+echo DefaultLimitNOFILE=102400 >> /etc/systemd/user.conf
+```
+
+#### 3. reexec **systemd**
+
+```bash
+systemctl daemon-reexec
+```
+
+#### 4. restart glider service
+
+```bash
+systemctl restart glider@server
+```
+
+#### 5. check the limits of PID
+
+```bash
+cat /proc/PID/limits
+```