Linux修改进程名称(setproctitle())

每一个c程序都有个main函数，作为程序启动入口函数。main函数的原型是int main(int argc , char *argv[]);其中argc表示命令行参数的个数；argv是一个指针数组，保存所有命令行字符串。Linux进程名称是通过命令行参数argv[0]来表示的。

Linux 还有环境变量参数信息，表示进程执行需要的所有环境变量信息。通过全局变量

Char **environ;可以访问环境变量。

命令行参数argv和环境变量信息environ是在一块连续的内存中表示的，并且environ紧跟在argv后面。如下图：

1.2 验证argv和environ执行连续内存的测试程序

1 #include <stdio.h>

2 #include <string.h>

3

4 extern char **environ;

5 int main(int argc , char *argv[])

6 {

7 int i;

8

9 printf("argc:%d\n" , argc);

10

11 for (i = 0; i < argc; ++i){

12 printf("%x\n" , argv[i]);

13 printf("argv[%d]:%s\n" , i , argv[i]);

14 }

15

16 printf("evriron=%x\n" , environ[0]);

17

18 return 0;

19 }

root@VM-Ubuntu203001:~/test#gcc -o test main.c

root@VM-Ubuntu203001:~/test#./test -p /usr/local/nginx -n 32

argc:5

bfa0c8f2

argv[0]:./test

bfa0c8f9

argv[1]:-p

bfa0c8fc

argv[2]:/usr/local/nginx

bfa0c90d

argv[3]:-n

bfa0c910

argv[4]:32

evriron=bfa0c913

1.3 修改进程名称

按理说，修改进程名称，只需要修改argv[0]指向的内存的值为所需要的值即可。但是当我们要修改的值超过argv[0]所指向的内存空间大小时，再这样直接修改，就会覆盖掉一部分argv[1]的值，因为从上面的图中，很容易就可以看出。

这时候，该怎么做呢？

1、必须重新分配一块连续的内存空间，把argv和environ的参数都复制到新的空间。

2、修改argv[0]为所需要修改的值。

1.4 Nginx的做法

* To change the process title in Linux andSolaris we have to set argv[1]

* to NULL and to copy the title to the sameplace where the argv[0] points to.

* However, argv[0] may be too small to hold anew title. Fortunately, Linux

* and Solaris store argv[] and environ[] oneafter another. So we should

* ensure that is the continuous memory andthen we allocate the new memory

* for environ[] and copy it. After this we could use the memory starting

* from argv[0] for our process title.

*

* The Solaris's standard /bin/ps does not showthe changed process title.

* You have to use "/usr/ucb/ps -w"instead. Besides, the UCB ps does not

* show a new title if its length less than theorigin command line length.

* To avoid it we append to a new title theorigin command line in the

* parenthesis.

*/

extern char **environ;

static char *ngx_os_argv_last;

ngx_int_t

ngx_init_setproctitle(ngx_log_t *log)

{

u_char *p;

size_t size;

ngx_uint_t i;

size = 0;

for (i = 0; environ[i]; i++) {

size+= ngx_strlen(environ[i]) + 1;

}

p = ngx_alloc(size, log);

if (p == NULL) {

return NGX_ERROR;

}

/*

这是为了找出argv和environ指向连续内存空间结尾的位置，为了能处理argv[i]被修改后，指向非进程启动时所分配的连续内存，而采用了下面的算法。但是实际上，这样还是处理不了这种情况。仅仅是个人愚见！！！

*/

ngx_os_argv_last= ngx_os_argv[0];

for (i = 0; ngx_os_argv[i]; i++) {

if (ngx_os_argv_last == ngx_os_argv[i]) {

ngx_os_argv_last= ngx_os_argv[i]+ ngx_strlen(ngx_os_argv[i]) + 1;

}

}

for (i = 0; environ[i]; i++) {

if (ngx_os_argv_last == environ[i]) {

size= ngx_strlen(environ[i]) + 1;

ngx_os_argv_last= environ[i]+ size;

ngx_cpystrn(p, (u_char *) environ[i], size);

environ[i] = (char *) p;

p+= size;

}

}

ngx_os_argv_last--;

return NGX_OK;

}

void

ngx_setproctitle(char *title)

{

u_char *p;

#if (NGX_SOLARIS)

ngx_int_t i;

size_t size;

#endif

ngx_os_argv[1]= NULL;

p = ngx_cpystrn((u_char*) ngx_os_argv[0], (u_char*) "nginx: ",

ngx_os_argv_last- ngx_os_argv[0]);

p = ngx_cpystrn(p, (u_char *) title, ngx_os_argv_last - (char*) p);

#if (NGX_SOLARIS)

size = 0;

for (i = 0; i < ngx_argc; i++) {

size+= ngx_strlen(ngx_argv[i]) + 1;

}

if (size > (size_t)((char *) p - ngx_os_argv[0])) {

/*

* ngx_setproctitle() is too rareoperation so we use

* the non-optimized copies

*/

p = ngx_cpystrn(p, (u_char *) " (",ngx_os_argv_last - (char*) p);

for (i = 0; i < ngx_argc; i++) {

p= ngx_cpystrn(p,(u_char *) ngx_argv[i],

ngx_os_argv_last - (char*) p);

p= ngx_cpystrn(p,(u_char *) "", ngx_os_argv_last - (char *) p);

}

if (*(p - 1) == ' ') {

*(p- 1) = ')';

}

}

#endif

if (ngx_os_argv_last - (char*) p) {

ngx_memset(p, NGX_SETPROCTITLE_PAD,ngx_os_argv_last - (char*) p);

}

ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,

"setproctitle:\"%s\"", ngx_os_argv[0]);

}