[转帖]TiDB 6.1 单机环境 On openEular 2003 SP3
https://tidb.net/book/book-rush/best-practice/other-practice/tidb61-on-openEular2003
背景
最近对国产操作系统很感兴趣,也有一些场景需要验证落地,官方支持银河麒麟 V10(X86,ARM),统信 UOS 等国产操作系统,但上述系统不是开源操作系统,使用上存在一些障碍,经过朋友推荐,选择华为的 openEular 进行验证测试。

目前 openEular 的 LTS 版本主要是 2003 和 2203 两个版本,2003 是 gcc 7+ 和 python 2.X 的环境,2203 是 gcc 10+ 和 python 3.X 的环境,理论上讲 2003 更接近目前所使用的 CentOS 7,兄弟组用 2203 编译 Doris 也遇到一些问题,因此选择 openEular 2003 SP3 进行测试。本次测试主要验证功能,分为部署过程测试和基本 SQL 查询测试,不做性能测试。openEular 同时支持 X86 和 ARM 架构,TiDB 也支持上述两种架构,本次测试中采用 X86_64 架构硬件设备进行测试。
本文使用 TiDB 6.1 作为测试版本,验证结果不保证可复现在 6.X 之前的版本上。
阅读受益
本文参照官方文档操作,验证 TiDB 运行在 openEular 上的可行性,为有选型需求的同学做一些参考。
本文记录了整个部署过程中的标准输出,对于只是想了解 TiDB 部署安装过程的同学,有一定参考价值。
经过本文的验证,在 openEular 部署使用 TiDB 与在 Centos 7 部署使用 TiDB 基本一致。部署过程中遇到的问题见最后的错误排查。
单机环境部署
部署环境
openEular 2003 SP3 4C8G Vmware 虚拟机 x86_64 环境
系统组件准备
由于系统的原因,需要提前安装以下组件:
yum -y install bc
集群拓扑
最小规模的 TiDB 集群拓扑:
| 实例 | 个数 | IP | 配置 |
|---|---|---|---|
| TiKV | 3 | 192.168.180.140 | 修改端口 |
| TiDB | 1 | 192.168.180.140 | 默认配置 |
| PD | 1 | 192.168.180.140 | 默认配置 |
| TiFlash | 1 | 192.168.180.140 | 默认配置 |
| Monitor | 1 | 192.168.180.140 | 默认配置 |
部署过程
- 下载并安装 TiUP:
[root@localhost tidb]## curl --proto '=https' --tlsv1.2 -sSf https://tiup-mirrors.pingcap.com/install.sh | sh
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 6968k 100 6968k 0 0 600k 0 0:00:11 0:00:11 --:--:-- 1129k
WARN: adding root certificate via internet: https://tiup-mirrors.pingcap.com/root.json
You can revoke this by remove /root/.tiup/bin/7b8e153f2e2d0928.root.json
Successfully set mirror to https://tiup-mirrors.pingcap.com
Detected shell: bash
Shell profile: /root/.bash_profile
/root/.bash_profile has been modified to add tiup to PATH
open a new terminal or source /root/.bash_profile to use it
Installed path: /root/.tiup/bin/tiup
===============================================
Have a try: tiup playground
===============================================
- 声明全局环境变量:
[root@localhost tidb]## source /root/.bash_profile
- 安装 TiUP 的 cluster 组件:
[root@localhost tidb]## tiup cluster
tiup is checking updates for component cluster ...timeout!
The component `cluster` version is not installed; downloading from repository.
download https://tiup-mirrors.pingcap.com/cluster-v1.10.1-linux-amd64.tar.gz 8.28 MiB / 8.28 MiB 100.00% 1.05 MiB/s
Starting component `cluster`: /root/.tiup/components/cluster/v1.10.1/tiup-cluster
Deploy a TiDB cluster for production
......
Use "tiup cluster help [command]" for more information about a command.
- 调大 sshd 服务的连接数限制:
[root@localhost tidb]## sed -i 's/##MaxSessions 10/MaxSessions 20/g' /etc/ssh/sshd_config
[root@localhost tidb]## service sshd restart
Redirecting to /bin/systemctl restart sshd.service
- 创建并启动集群 创建配置文件 topo.yaml:
## ## Global variables are applied to all deployments and used as the default value of
## ## the deployments if a specific deployment value is missing.
global:
user: "tidb"
ssh_port: 22
deploy_dir: "/tidb-deploy"
data_dir: "/tidb-data"
## ## Monitored variables are applied to all the machines.
monitored:
node_exporter_port: 9100
blackbox_exporter_port: 9115
server_configs:
tidb:
log.slow-threshold: 300
tikv:
readpool.storage.use-unified-pool: false
readpool.coprocessor.use-unified-pool: true
pd:
replication.enable-placement-rules: true
replication.location-labels: ["host"]
tiflash:
logger.level: "info"
pd_servers:
- host: 192.168.180.140
tidb_servers:
- host: 192.168.180.140
tikv_servers:
- host: 192.168.180.140
port: 20160
status_port: 20180
config:
server.labels: {host: "logic-host-1"}
- host: 192.168.180.140
port: 20161
status_port: 20181
config:
server.labels: {host: "logic-host-2"}
- host: 192.168.180.140
port: 20162
status_port: 20182
config:
server.labels: {host: "logic-host-3"}
tiflash_servers:
- host: 192.168.180.140
monitoring_servers:
- host: 192.168.180.140
grafana_servers:
- host: 192.168.180.140
部署集群:
[root@localhost tidb]## tiup cluster deploy tidb61 v6.1.0 ./topo.yaml --user root -p
tiup is checking updates for component cluster ...
Starting component `cluster`: /root/.tiup/components/cluster/v1.10.1/tiup-cluster deploy tidb61 v6.1.0 ./topo.yaml --user root -p
Input SSH password:
+ Detect CPU Arch Name
- Detecting node 192.168.180.140 Arch info ... Done
+ Detect CPU OS Name
- Detecting node 192.168.180.140 OS info ... Done
Please confirm your topology:
Cluster type: tidb
Cluster name: tidb61
Cluster version: v6.1.0
......
Attention:
1. If the topology is not what you expected, check your yaml file.
2. Please confirm there is no port/directory conflicts in same host.
Do you want to continue? [y/N]: (default=N) y
+ Generate SSH keys ... Done
+ Download TiDB components
+ Download TiDB components
+ Initialize target host environments
+ Deploy TiDB instance
+ Copy certificate to remote host
+ Init instance configs
+ Init monitor configs
+ Check status
Enabling component pd
Enabling component tikv
Enabling component tidb
Enabling component tiflash
Enabling component prometheus
Enabling component grafana
Enabling component node_exporter
Enabling component blackbox_exporter
Cluster `tidb61` deployed successfully, you can start it with command: `tiup cluster start tidb61 --init`
启动集群:
[root@ecs-5842 ~]## tiup cluster start tidb61 --init
tiup is checking updates for component cluster ...
Starting component `cluster`: /root/.tiup/components/cluster/v1.10.1/tiup-cluster start tidb61 --init
Starting cluster tidb61...
......
Started cluster `tidb61` successfully
The root password of TiDB database has been changed.
The new password is: '5%thkE=sL6^-1382wV'.
Copy and record it to somewhere safe, it is only displayed once, and will not be stored.
The generated password can NOT be get and shown again.
查看集群状态:
[root@ecs-5842 ~]## tiup cluster display tidb61
tiup is checking updates for component cluster ...timeout!
Starting component `cluster`: /root/.tiup/components/cluster/v1.10.1/tiup-cluster display tidb61
Cluster type: tidb
Cluster name: tidb61
Cluster version: v6.1.0
Deploy user: tidb
SSH type: builtin
Dashboard URL: http://192.168.0.141:2379/dashboard
Grafana URL: http://192.168.0.141:3000
ID Role Host Ports OS/Arch Status Data Dir Deploy Dir
-- ---- ---- ----- ------- ------ -------- ----------
192.168.0.141:3000 grafana 192.168.0.141 3000 linux/x86_64 Up - /tidb-deploy/grafana-3000
192.168.0.141:2379 pd 192.168.0.141 2379/2380 linux/x86_64 Up|L|UI /tidb-data/pd-2379 /tidb-deploy/pd-2379
192.168.0.141:9090 prometheus 192.168.0.141 9090/12020 linux/x86_64 Up /tidb-data/prometheus-9090 /tidb-deploy/prometheus-9090
192.168.0.141:4000 tidb 192.168.0.141 4000/10080 linux/x86_64 Up - /tidb-deploy/tidb-4000
192.168.0.141:9000 tiflash 192.168.0.141 9000/8123/3930/20170/20292/8234 linux/x86_64 Up /tidb-data/tiflash-9000 /tidb-deploy/tiflash-9000
192.168.0.141:20160 tikv 192.168.0.141 20160/20180 linux/x86_64 Up /tidb-data/tikv-20160 /tidb-deploy/tikv-20160
192.168.0.141:20161 tikv 192.168.0.141 20161/20181 linux/x86_64 Up /tidb-data/tikv-20161 /tidb-deploy/tikv-20161
192.168.0.141:20162 tikv 192.168.0.141 20162/20182 linux/x86_64 Up /tidb-data/tikv-20162 /tidb-deploy/tikv-20162
Total nodes: 8
测试 TiKV 和 TiFlash 查询
生成基础环境
[root@ecs-5842 ~]## tiup install bench
[root@ecs-5842 ~]## tiup bench tpch prepare -p 5%thkE=sL6^-1382wV
tiup is checking updates for component bench ...
Starting component `bench`: /root/.tiup/components/bench/v1.10.1/tiup-bench tpch prepare -p 5%thkE=sL6^-1382wV
creating nation
creating region
creating part
creating supplier
creating partsupp
creating customer
creating orders
creating lineitem
generating nation table
generate nation table done
generating region table
generate region table done
generating customers table
generate customers table done
generating suppliers table
generate suppliers table done
generating part/partsupplier tables
generate part/partsupplier tables done
generating orders/lineitem tables
generate orders/lineitem tables done
Finished
下载并安装一下 rpm 包:
mysql-community-client-5.7.35-1.el7.x86_64.rpm
mysql-community-common-5.7.35-1.el7.x86_64.rpm
mysql-community-libs-5.7.35-1.el7.x86_64.rpm
[root@ecs-5842 ~]## rpm -ivh mysql-community-*
warning: mysql-community-client-5.7.35-1.el7.x86_64.rpm: Header V3 DSA/SHA256 Signature, key ID 5072e1f5: NOKEY
Verifying... ################################################################## [100%]
Preparing... ################################################################## [100%]
Updating / installing...
1:mysql-community-common-5.7.35-1.e################################################################## [33%]
2:mysql-community-libs-5.7.35-1.el7################################################################## [67%]
3:mysql-community-client-5.7.35-1.e################################################################## [100%]
TiKV 查询
[root@ecs-5842 ~]## mysql -h 192.168.0.141 -P 4000 -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 421
Server version: 5.7.25-TiDB-v6.1.0 TiDB Server (Apache License 2.0) Community Edition, MySQL 5.7 compatible
Copyright (c) 2000, 2021, Oracle and/or its affiliates.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> SELECT
-> l_orderkey,
-> SUM(-> l_extendedprice * (1 - l_discount)
-> ) AS revenue,
-> o_orderdate,
-> o_shippriority
-> FROM
-> customer,
-> orders,
-> lineitem
-> WHERE
-> c_mktsegment = 'BUILDING'
-> AND c_custkey = o_custkey
-> AND l_orderkey = o_orderkey
-> AND o_orderdate < DATE '1996-01-01'
-> AND l_shipdate > DATE '1996-02-01'
-> GROUP BY
-> l_orderkey,
-> o_orderdate,
-> o_shippriority
-> ORDER BY
-> revenue DESC,
-> o_orderdate
-> limit 10;
+------------+-------------+-------------+----------------+
| l_orderkey | revenue | o_orderdate | o_shippriority |
+------------+-------------+-------------+----------------+
| 5828933 | 386117.1688 | 1995-12-03 | 0 |
| 1648647 | 373096.8642 | 1995-12-06 | 0 |
| 1364641 | 352640.6056 | 1995-12-19 | 0 |
| 3949606 | 347750.4435 | 1995-12-23 | 0 |
| 4792161 | 347715.0509 | 1995-12-30 | 0 |
| 4340739 | 347490.5251 | 1995-12-06 | 0 |
| 1609574 | 342497.8886 | 1995-12-31 | 0 |
| 3076934 | 338202.3259 | 1995-12-24 | 0 |
| 3232933 | 337349.2536 | 1995-12-26 | 0 |
| 2345058 | 335142.6104 | 1995-12-31 | 0 |
+------------+-------------+-------------+----------------+
10 rows in set (1.71 sec)
TiFlash 查询
mysql> ALTER TABLE test.customer SET TIFLASH REPLICA 1;
Query OK, 0 rows affected (0.07 sec)
mysql> ALTER TABLE test.orders SET TIFLASH REPLICA 1;
Query OK, 0 rows affected (0.08 sec)
mysql> ALTER TABLE test.lineitem SET TIFLASH REPLICA 1;
Query OK, 0 rows affected (0.08 sec)
mysql> SELECT * FROM information_schema.tiflash_replica WHERE TABLE_SCHEMA = 'test' ;
+--------------+------------+----------+---------------+-----------------+-----------+----------+
| TABLE_SCHEMA | TABLE_NAME | TABLE_ID | REPLICA_COUNT | LOCATION_LABELS | AVAILABLE | PROGRESS |
+--------------+------------+----------+---------------+-----------------+-----------+----------+
| test | customer | 79 | 1 | | 1 | 1 |
| test | orders | 81 | 1 | | 1 | 1 |
| test | lineitem | 83 | 1 | | 1 | 1 |
+--------------+------------+----------+---------------+-----------------+-----------+----------+
3 rows in set (0.00 sec)
mysql> SELECT
-> l_orderkey,
-> SUM(-> l_extendedprice * (1 - l_discount)
-> ) AS revenue,
-> o_orderdate,
-> o_shippriority
-> FROM
-> customer,
-> orders,
-> lineitem
-> WHERE
-> c_mktsegment = 'BUILDING'
-> AND c_custkey = o_custkey
-> AND l_orderkey = o_orderkey
-> AND o_orderdate < DATE '1996-01-01'
-> AND l_shipdate > DATE '1996-02-01'
-> GROUP BY
-> l_orderkey,
-> o_orderdate,
-> o_shippriority
-> ORDER BY
-> revenue DESC,
-> o_orderdate
-> limit 10;
+------------+-------------+-------------+----------------+
| l_orderkey | revenue | o_orderdate | o_shippriority |
+------------+-------------+-------------+----------------+
| 5828933 | 386117.1688 | 1995-12-03 | 0 |
| 1648647 | 373096.8642 | 1995-12-06 | 0 |
| 1364641 | 352640.6056 | 1995-12-19 | 0 |
| 3949606 | 347750.4435 | 1995-12-23 | 0 |
| 4792161 | 347715.0509 | 1995-12-30 | 0 |
| 4340739 | 347490.5251 | 1995-12-06 | 0 |
| 1609574 | 342497.8886 | 1995-12-31 | 0 |
| 3076934 | 338202.3259 | 1995-12-24 | 0 |
| 3232933 | 337349.2536 | 1995-12-26 | 0 |
| 2345058 | 335142.6104 | 1995-12-31 | 0 |
+------------+-------------+-------------+----------------+
10 rows in set (0.40 sec)
查看执行计划:
经过分析发现,查询走的 tiflash,因为出现 ExchangeSender 和 ExchangeReceiver 算子,表明 MPP 已生效。
错误排查
sudo 权限
当遇到如下错误时:
Error: executor.ssh.execute_failed: Failed to execute command over SSH for 'tidb@192.168.0.141:22' {ssh_stderr: We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:
##1) Respect the privacy of others.
##2) Think before you type.
##3) With great power comes great responsibility.
sudo: no tty present and no askpass program specified
, ssh_stdout: , ssh_command: export LANG=C; PATH=$PATH:/bin:/sbin:/usr/bin:/usr/sbin /usr/bin/sudo -H bash -c "test -d /tidb-deploy || (mkdir -p /tidb-deploy && chown tidb:$(id -g -n tidb) /tidb-deploy)"}, cause: Process exited with status 1
需要添加 sudo 权限:
visudo
tidb ALL=(ALL) NOPASSWD: ALL
内存问题
当发现以下错误时:
goroutine 1 [running]:
runtime/debug.Stack()
/usr/local/go/src/runtime/debug/stack.go:24 +0x65
runtime/debug.PrintStack()
/usr/local/go/src/runtime/debug/stack.go:16 +0x19
github.com/pingcap/tidb/session.mustExecute({0x42f39c0?, 0xc001078480?}, {0x3dd5b11?, 0x145e707?}, {0xc0016c9780?, 0x37741a0?, 0x1?})
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/bootstrap.go:2087 +0x8a
github.com/pingcap/tidb/session.insertBuiltinBindInfoRow(...)
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/bootstrap.go:1461
github.com/pingcap/tidb/session.initBindInfoTable({0x42f39c0, 0xc001078480})
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/bootstrap.go:1457 +0xb1
github.com/pingcap/tidb/session.doDDLWorks({0x42f39c0, 0xc001078480})
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/bootstrap.go:1941 +0x2c9
github.com/pingcap/tidb/session.bootstrap({0x42f39c0?, 0xc001078480?})
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/bootstrap.go:445 +0x2ab
github.com/pingcap/tidb/session.runInBootstrapSession({0x42b5ff0, 0xc000b825a0}, 0x3e27620)
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/session.go:2941 +0x1ff
github.com/pingcap/tidb/session.BootstrapSession({0x42b5ff0, 0xc000b825a0})
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/session/session.go:2829 +0x216
main.createStoreAndDomain()
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/tidb-server/main.go:296 +0x114
main.main()
/home/jenkins/agent/workspace/build-common/go/src/github.com/pingcap/tidb/tidb-server/main.go:202 +0x4ca
可能是内存不足,由原有的 8G 扩展到 32G 后,问题没有复现。
总结
经过以上验证,用最简单的方式验证了 openEular 2003 SP3 系统下 TiDB 的部署安装和简单的功能验证。由于环境所限,没有经过更多的功能测试和性能测试,在充分的使用和验证后,再行文贡献给大家。
[转帖]TiDB 6.1 单机环境 On openEular 2003 SP3的更多相关文章
- MongoDB3.0.x版本用户授权配置(单机环境)
MongoDB数据库默认情况下是没有做权限控制的,只要能够连接所开放的端口就能进行访问,而且拥有root级别的权限:对于生产环境而言是极不安全的,所以需要建立用户,进行授权控制. 单机环境下的用户授权 ...
- Kafka单机环境部署
前面说过Kafka集群环境的部署,现在主要说一下在本地测试中Kafka单机环境的部署,和前面一样首先保证zookeeper服务的正常运行,然后解压并释放kafka安装包,并放到指定位置: tar -x ...
- storm单机环境部署
前面说过storm集群的部署,这篇主要介绍storm单机环境部署,其实他们之间很类似,就是将之前配置文件中所有的集群条目改成本机的地址即可,部署之前应该按前面solr和zookeeper单机环境部署那 ...
- solr单机环境配置并包含外部单机zookeeper
首先和之前一样下载solr-5.3.1.tgz,然后执行下面命令释放文件并放置在/usr/目录下: $ .tgz $ /usr/ $ cd /usr/solr- 这个时候先不用启动solr,因为单机模 ...
- BizTalk开发系列(三) 单机环境下的BizTalk Server 2006 R2安装
大部分的开发环境都是在单机环境下进行的,今天整理了一下BizTalk Server 2006 R2在单机环境下的安装步骤. 1. 软件需求 在独立服务器中完整安装BizTalk Server 2006 ...
- 科谱,如何单机环境下合理的备份mssql2008数据库
前言: 终于盼来了公司的自用服务器:1U.至强CPU 1.8G 4核.16G内存.500G硬盘 X 2 (RAID1);装了64位win2008,和64位mssql2008.仔细把玩了一天把新老业务系 ...
- hbase单机环境的搭建和完全分布式Hbase集群安装配置
HBase 是一个开源的非关系(NoSQL)的可伸缩性分布式数据库.它是面向列的,并适合于存储超大型松散数据.HBase适合于实时,随机对Big数据进行读写操作的业务环境. @hbase单机环境的搭建 ...
- 安装spark1.3.1单机环境
本文介绍安装spark单机环境的方法,可用于测试及开发.主要分成以下4部分: (1)环境准备 (2)安装scala (3)安装spark (4)验证安装情况 1.环境准备 (1)配套软件版本要求:Sp ...
- windows7 spark单机环境搭建及pycharm访问spark
windows7 spark单机环境搭建 follow this link how to run apache spark on windows7 pycharm 访问本机 spark 安装py4j ...
- Twitter Storm:单机环境的安装与配置
Twitter Storm:单机环境的安装与配置 好久没写博客了,这一段时间一直被导师push着做毕业设计.由于目前的方向偏向于图像识别检索,毕设打算做一个基于分布式计算平台的图像检索系统,查阅相关资 ...
随机推荐
- linux文件摘选
显示/var目录下所有以1开头,以一个小写字母结尾,且中间至少出现一位数字(可以由其他字符)的文件或目录. 命令: ls -d /var/1*[0-9]*[a-z] [root@foundation0 ...
- Weblogic获取端口IP
Weblogic获取端口IP 获取端口IP只为了判断哪个节点 调用 private WebMBeanServer server=new WebMBeanServer(); synlog.info(&q ...
- Java日期时间处理详解
Java中SimpleDateFormat.LocalDateTime和DateTimeFormatter的区别及使用 在Java的世界里,处理日期和时间是常见的任务.尤其在Java 8之前,Simp ...
- 华为云GaussDB数据库荣获国际CC EAL4+级别认证
摘要:近日,华为云GaussDB企业级分布式数据库内核正式通过了全球知名独立认证机构欧洲SGS Brightsight实验室的安全评估,获得全球权威信息技术安全性评估标准CC EAL4+级别认证. 本 ...
- 解读知识蒸馏模型TinyBert
摘要:本篇文章的重点在于改进信息瓶颈的优化机制,并且围绕着高纬空间中互信息难以估计,以及信息瓶颈优化机制中的权衡难题这两个点进行讲解. 本文分享自华为云社区<[云驻共创]美文赏析:大佬对变分蒸馏 ...
- 大力出奇迹,揭秘昇腾CANN的AI超能力
摘要:CANN(Compute Architecture for Neural Networks)异构计算架构,是以提升用户开发效率和释放昇腾AI处理器极致算力为目标,专门面向AI场景的异构计算架构. ...
- Solon Web 开发:三、一个简单的 Web 模板项目(或示例)
演示 web 程序的常用能力: 控制器.请求参数.参数校验.跳转 过滤器.全局异常处理 静态文件 动态模板 动态模板公共变量及控制器基类 日志 Json 渲染格式控制 模板下载: 打包成 jar ,可 ...
- MyBatis 核心组件 —— Configuration
概述 Mybatis 的核心组件如下所示: Configuration:用于描述 MyBatis 的主配置信息,其他组件需要获取配置信息时,直接通过 Configuration 对象获取.除此之外,M ...
- 【python爬虫】requests高级用法 代理池搭建 爬虫实战
目录 昨日回顾 面试题 爬虫总结 今日内容 1 requests高级用法 1.0 解析json 1.1 ssl认证(了解) 1.2 使用代理(重要) 1.3 超时设置 1.4 异常处理 1.5 上传文 ...
- 文件描述符&文件句柄
一.概念 1.1 文件描述符&文件描述符表 文件描述符(file descriptor, fd)是Linux系统中对已打开文件的一个抽象标记,所有I/O系统调用对已打开文件的操作都要用到它.这 ...