更新包下载目录更改为cache目录后，下载的更新包需要修改权限才能进入安装状态

app/src/main/java/com/bgycc/smartcanteen/command/UpdateCommandHandler.java

 package com.bgycc.smartcanteen.command;
 
+import android.os.Build;
+
 import com.bgycc.smartcanteen.BuildConfig;
 import com.bgycc.smartcanteen.api.SCRetrofit;
 import com.bgycc.smartcanteen.entity.Command;
@@ -165,9 +167,23 @@ public class UpdateCommandHandler extends CommandHandler {
                 LogUtils.d(TAG, "不允许安装低版本");
                 failed("不允许安装低版本", 0);
             } else {
-                DangerousUtils.installAppSilent(updateApk);
-                LogUtils.d(TAG, "开始安装");
-                success("开始安装", 100);
+                if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.M) {
+                    // 6.0以下安装包需要修改权限才能安装
+                    try {
+                        Process p = Runtime.getRuntime().exec("chmod 755 " + updateApk);
+                        p.waitFor();
+                        DangerousUtils.installAppSilent(updateApk);
+                        LogUtils.d(TAG, "开始安装");
+                        success("开始安装", 100);
+                    } catch (Exception e) {
+                        LogUtils.e(TAG, "安装文件权限修改失败");
+                        failed("安装文件权限修改失败", 0);
+                    }
+                } else {
+                    DangerousUtils.installAppSilent(updateApk);
+                    LogUtils.d(TAG, "开始安装");
+                    success("开始安装", 100);
+                }
             }
             try {
                 Thread.sleep(DEFAULT_DELAY);