> ## Content Index > Fetch the complete content index at: https://blog.hacking.pub/llms.txt > Use this file to discover other available public pages before exploring further. # Text file busy 问题粗解 - URL: https://blog.hacking.pub/2018/04/11/text-file-busy-wen-ti-xiang-jie/ - Published: 2018-04-11T12:30:03.000Z - Updated: 2018-04-11T12:30:03.000Z - Author: chainhelen - Tags: text file busy, inode, linux, 热重启, 平滑重启 #### 1\. 问题起源 接手一个评论的项目，是用golang写的，采用了gin的web框架 发现里面并没有做热重启，尝试去了解了一下[文档](https://github.com/gin-gonic/gin?ref=blog.hacking.pub) 推荐了一个[endless](https://github.com/fvbock/endless?ref=blog.hacking.pub)的平滑重启库 当我尝试里面写的[事例](https://github.com/fvbock/endless/tree/master/examples?ref=blog.hacking.pub)时候，会报错 文档里面提及的操作如下： ``` Compile the example $ go build -o simple_server examples/simple.go Run it $ ./simple_server 2015/03/22 20:03:29 PID: 2710 localhost:4242 Make a request $ curl http://localhost:4242/hello WORLD! Change the handler - eg. replace the ! with a ? $ go build -o simple_server examples/simple.go $ kill -1 2710 The server log says something like: 2015/03/22 20:04:10 2710 Received SIGHUP. forking. 2015/03/22 20:04:10 2710 Received SIGTERM. 2015/03/22 20:04:10 2710 Waiting for connections to finish... 2015/03/22 20:04:10 PID: 2726 localhost:4242 2015/03/22 20:04:10 accept tcp 127.0.0.1:4242: use of closed network connection 2015/03/22 20:04:10 Server on 4242 stopped Make another request $ curl http://localhost:4242/hello WORLD? ``` 实际操作如下: ``` [root@localhost examples]# go build -o simple simple.go [root@localhost examples]# ./simple & [1] 2638 [root@localhost examples]# 2018/04/09 01:50:10 2638 localhost:4242 [root@localhost examples]# go build -o simple simple.go go install command-line-arguments: open simple: text file busy ``` ##### 2\. 跳坑 先提前说一件事，就是我上面的代码是跑在本地的vbox虚拟机上的，系统cetenos7 而代码路径是共享的，也就是说我 宿主机windows 10 和 虚拟机centenos7 都能访问到 这里是一个坑，先跳过去不说，先解释一下普遍遇到`text file busy` 问题的情况 #### 3\. 分析 目的主要是希望修改已经运行的二进制文件，会对运行中的程序造成的影响 不免俗套跟网上一样，采用cp、mv、rm几个命令来看 事例代码如下 ``` // a.c #include #include int main() { printf("hello world2\n"); sleep(10000000); return 0; } ``` #### 4\. cp 先尝试修改`cp` ``` [root@localhost ~]# gcc a.c -o a // 编译a.c [root@localhost ~]# ./a & //后台执行程序 a [2] 3903 // 回显 [root@localhost ~]# hello world2 //程序a的输出 [root@localhost ~]# mkdir ./tmp //创建./tmp目录 [root@localhost ~]# cd ./tmp/ //进入./tmp目录 [root@localhost tmp]# gcc ../a.c -o a //重新编译生成一个可执行文件a，在./tmp目录 // 情况一 cp 不加 -f [root@localhost tmp]# cp a ../ //把./tmp/a的可执行文件覆盖到上一层 //注意：上一层的可执行文件已经运行了 cp: overwrite ‘../a’? y cp: cannot create regular file ‘../a’: Text file busy //报错 // 情况二 cp 加 -f [root@localhost tmp]# cp -f a ../ cp: overwrite ‘../a’? y [root@localhost tmp]# //无回显成功 ``` ``` [root@localhost tmp]# strace cp a ../ 2>&1 | grep -C 3 'busy' //观察一下 stat("../a", {st_mode=S_IFREG|0755, st_size=8560, ...}) = 0 open("a", O_RDONLY) = 3 fstat(3, {st_mode=S_IFREG|0755, st_size=8560, ...}) = 0 open("../a", O_WRONLY|O_TRUNC) = -1 ETXTBSY (Text file busy) open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4 fstat(4, {st_mode=S_IFREG|0644, st_size=2502, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f8b718dc000 [root@localhost tmp]# strace cp -f a ../ 2>&1 ... open("a", O_RDONLY) = 3 fstat(3, {st_mode=S_IFREG|0755, st_size=8560, ...}) = 0 open("../a", O_WRONLY|O_TRUNC) = -1 ETXTBSY (Text file busy) unlink("../a") = 0 open("../a", O_WRONLY|O_CREAT|O_EXCL, 0755) = 4 fstat(4, {st_mode=S_IFREG|0755, st_size=0, ...}) = 0 fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\2\0>\0\1\0\0\0\220\4@\0\0\0\0 ... ``` `cp`有`-f`参数的时候，发生`open ../a`报`Text file busy`失败，会去`unlink("../a")` ##### 5.inode ``` An inode stores all the information about a regular file, directory, or other file system object, except its data and name. ``` 说清楚下面内容之前，得先说清楚inode 文件存储在硬盘上，硬盘的最小存储单位叫做“扇区”（Sector），每个扇区存储512字节（相当于0.5字节） 多个扇区组成的“块”（block），是文件的存储最小单位，最常见的是4kB即8扇区组成块 inode 包含文件的元信息，具体如下 1.文件的字节数 2.文件拥有者的User ID 3.文件的Group ID 4.文件的读、写、执行权限 5.文件的时间戳，共有三个：ctime指inode上一次变动时间； mtime文件内容上一次变动时间；atime指文件上一次打开时间 6.链接数，即有多少文件名指向这个inode 7.文件数据block的位置 stat 命令常看具体某个文件的inode情况 ``` [root@localhost tmp]# stat a File: ‘a’ Size: 8560 Blocks: 24 IO Block: 4096 regular file Device: fd00h/64768d Inode: 13662766 Links: 1 Access: (0755/-rwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:object_r:admin_home_t:s0 Access: 2018-04-09 11:00:57.379173943 -0400 Modify: 2018-04-09 10:50:37.684332780 -0400 Change: 2018-04-09 10:50:37.684332780 -0400 Birth: - [root@localhost tmp]# ln a a.ww [root@localhost tmp]# stat a File: ‘a’ Size: 8560 Blocks: 24 IO Block: 4096 regular file Device: fd00h/64768d Inode: 13662766 Links: 2 Access: (0755/-rwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:object_r:admin_home_t:s0 Access: 2018-04-09 11:00:57.379173943 -0400 Modify: 2018-04-09 10:50:37.684332780 -0400 Change: 2018-04-09 12:38:19.527611751 -0400 ``` ##### 6.它山之石 找到一篇文章写得非常详细[知乎专栏](https://zhuanlan.zhihu.com/p/25600743?ref=blog.hacking.pub)，我这里重复一下里面的实验 事实某些操作与文章所写不一样，可以注意下坑点 里面很多知识点，其实在《程序员的自我修养》里面都有深入讲解 一. 删除正在被读写的文件 ``` // 1.c #include #include #include #include #include #include #include #define BUFFER_SIZE 1024 int main(void) { int fd; int i = 0; char buffer[BUFFER_SIZE]; if ((fd=open("data.txt", O_RDONLY)) == -1) { printf("Open file Error\n"); exit(1); } int pid = getpid(); int n = 0; while(1) { ++i; n= read(fd, buffer, BUFFER_SIZE-1); if(n == -1) { printf("read Error\n"); exit(1); } buffer[n] = '\0'; printf("%d pid:%d, fd:%d, content: %s\n", i, pid, fd, buffer); sleep(1); lseek(fd, 0L, SEEK_SET); } close(fd); exit(0); } // data.txt [root@localhost ~]# cat data.txt hello world ``` 执行 ``` root@localhost ~]# gcc 1.c -o 1 [root@localhost ~]# ./1 1 pid:4525, fd:3, content: hello world 2 pid:4525, fd:3, content: hello world 3 pid:4525, fd:3, content: hello world 4 pid:4525, fd:3, content: hello world 5 pid:4525, fd:3, content: hello world 6 pid:4525, fd:3, content: hello world 7 pid:4525, fd:3, content: hello world ... ``` 上面程序`1`运行的时候，尝试查看进程中打开文件的inode、data.txt的inode、已经删除过后的inode情况 ``` [root@localhost ~]# ll /proc/4525/fd/3 lr-x------. 1 root root 64 Apr 9 13:11 /proc/4525/fd/3 -> /root/data.txt [root@localhost ~]# stat /proc/4525/fd/3 File: ‘/proc/4525/fd/3’ -> ‘/root/data.txt’ Size: 64 Blocks: 0 IO Block: 1024 symbolic link Device: 3h/3d Inode: 37044 Links: 1 Access: (0500/lr-x------) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 Access: 2018-04-09 13:11:04.923771194 -0400 Modify: 2018-04-09 13:11:04.923771194 -0400 Change: 2018-04-09 13:11:04.923771194 -0400 Birth: - [root@localhost ~]# stat /root/data.txt File: ‘/root/data.txt’ Size: 12 Blocks: 8 IO Block: 4096 regular file Device: fd00h/64768d Inode: 9543125 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:object_r:admin_home_t:s0 Access: 2018-04-09 13:10:24.335138927 -0400 Modify: 2018-04-09 13:10:22.605154600 -0400 Change: 2018-04-09 13:10:22.605154600 -0400 Birth: - // 删除过后 [root@localhost ~]# rm -rf /root/data.txt [root@localhost ~]# ll /proc/4525/fd/3 lr-x------. 1 root root 64 Apr 9 13:11 /proc/4525/fd/3 -> /root/data.txt (deleted) [root@localhost ~]# stat /proc/4525/fd/3 File: ‘/proc/4525/fd/3’ -> ‘/root/data.txt (deleted)’ Size: 64 Blocks: 0 IO Block: 1024 symbolic link Device: 3h/3d Inode: 37044 Links: 1 Access: (0500/lr-x------) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 Access: 2018-04-09 13:11:16.676664713 -0400 Modify: 2018-04-09 13:11:04.923771194 -0400 Change: 2018-04-09 13:11:04.923771194 -0400 Birth: - [root@localhost ~]# stat /root/data.txt stat: cannot stat ‘/root/data.txt’: No such file or directory ``` 上述程序，删除data.txt之前 程序中所打开的文件描述符/proc/pid/fd/index 其实是 文件本身/root/data.txt 的软链接 正因为是软链接(symbolic link)，所以两者的inode是不一样的 ``` /proc/4525/3/index 的 inode 是 37044 /root/data.txt 的 inode 是 9543125 ``` 这里看上去与文章中不一致，原因在于参数，需要加上`-L`，这样才能看到软链接对应文件的inode ``` -L, --dereference when showing file information for a symbolic link, show information for the file the link references rather than for the link itself ``` 有了以上基础，再来使用两个命令看一下这个软链接 ``` [root@localhost ~]# ls -i1L /proc/4525/fd/3 9543125 /proc/4525/fd/3 [root@localhost ~]# stat -L /proc/4525/fd/3 File: ‘/proc/4525/fd/3’ Size: 12 Blocks: 8 IO Block: 4096 regular file Device: fd00h/64768d Inode: 9543125 Links: 0 Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root) Context: unconfined_u:object_r:admin_home_t:s0 Access: 2018-04-09 13:11:35.405495030 -0400 Modify: 2018-04-09 13:10:22.605154600 -0400 Change: 2018-04-09 13:11:34.520503048 -0400 Birth: - ``` 当发生删除文件事，程序并没有发生崩溃，但是已经能看到软链接另一端已经被删除(deleted) 实际系统还是在删除过后，仍然保留了文件内容，直到所有进程都关闭了这一文件 （就算在删除过后手动新建了一个同名文件，那都是新的inode，跟正在运行程序的打开文件没有任何关系） 二. 删除、覆盖正在运行的程序，跟上面是一样的 三. 删除动态链接库，是一样的；但是覆盖操作是允许的，也就是说程序会出现异常