重启后如何处理陈旧的 pidfile?我想我不能相信文件中的数字,因为另一个进程可能已经用相同的 PID 取代了它的位置。
我可以/应该确保 pidfile 不会在重新启动后继续存在吗?当具有该 pid 的进程正在运行时,检测过时 pidfile 的正确方法是什么,该文件可能会或可能不会从先前的引导中遗留下来?
通常,pidfiles 被写入/var/run/
or /run/
(在许多系统上,有一个符号链接 from /var/run
to/run
所以它们是相同的)。有关更多信息,请参阅文件系统层次标准。并且该/run/
目录应该在启动时尽早清除(即因为它被挂载为tmpfs
),所以它不会在重新启动时存活。另请参阅Linux Standard Base 4.1规范。
因此,您不应该关心过时的 pidfile。这不应该发生,如果发生,可能是因为系统管理员把事情搞砸了。如果该 pidfile 已经存在,我会以某种错误消息退出。
/proc/PID/cmdine
如果这是您自己的守护进程,您可以通过扫描或发送信号以使用该 PID 进行处理来检测陈旧的 PID 文件。
对于一个简单的扫描示例,/proc
我展示了我的解决方案:
#define PROC_BASE "/proc"
#include <stdio.h> // printf, fopen, ...
#include <unistd.h> // getpid
#include <stdio.h> // perror
#include <sys/types.h> // opendir
#include <dirent.h> // opendir
#include <sys/stat.h> // stat
#include <fcntl.h> // fcntl
#include <stdlib.h> // exit
#include <string.h> // memset
/**
* read process name from /proc/PID/cmdline
* @param pid - PID of interesting process
* @return filename or NULL if not found
* don't use this function twice for different names without copying
* its returning by strdup, because `name` contains in static array
*/
char *readname(pid_t pid){
static char name[256];
char *pp = name, byte, path[256];
FILE *file;
int cntr = 0;
size_t sz;
snprintf (path, 255, PROC_BASE "/%d/cmdline", pid);
file = fopen(path, "r");
if(!file) return NULL; // there's no such file
do{ // read basename
sz = fread(&byte, 1, 1, file);
if(sz != 1) break;
if(byte != '/') *pp++ = byte;
else{
pp = name;
cntr = 0;
}
}while(byte && cntr++ < 255);
name[cntr] = 0;
fclose(file);
return name;
}
void iffound_default(pid_t pid){
fprintf(stderr, "\nFound running process (pid=%d), exit.\n", pid);
exit(0);
}
/**
* check wether there is a same running process
* exit if there is a running process or error
* Checking have 3 steps:
* 1) lock executable file
* 2) check pidfile (if you run a copy?)
* 3) check /proc for executables with the same name (no/wrong pidfile)
* @param argv - argument of main() or NULL for non-locking, call this function before getopt()
* @param pidfilename - name of pidfile or NULL if none
* @param iffound - action to run if file found or NULL for exit(0)
*/
void check4running(char **argv, char *pidfilename, void (*iffound)(pid_t pid)){
DIR *dir;
FILE *pidfile, *fself;
struct dirent *de;
struct stat s_buf;
pid_t pid = 0, self;
struct flock fl;
char *name, *myname;
if(!iffound) iffound = iffound_default;
if(argv){ // block self
fself = fopen(argv[0], "r"); // open self binary to lock
memset(&fl, 0, sizeof(struct flock));
fl.l_type = F_WRLCK;
if(fcntl(fileno(fself), F_GETLK, &fl) == -1){ // check locking
perror("fcntl");
exit(1);
}
if(fl.l_type != F_UNLCK){ // file is locking - exit
printf("Found locker, PID = %d!\n", fl.l_pid);
exit(1);
}
fl.l_type = F_RDLCK;
if(fcntl(fileno(fself), F_SETLKW, &fl) == -1){
perror("fcntl");
exit(1);
}
}
self = getpid(); // get self PID
if(!(dir = opendir(PROC_BASE))){ // open /proc directory
perror(PROC_BASE);
exit(1);
}
if(!(name = readname(self))){ // error reading self name
perror("Can't read self name");
exit(1);
}
myname = strdup(name);
if(pidfilename && stat(pidfilename, &s_buf) == 0){ // pidfile exists
pidfile = fopen(pidfilename, "r");
if(pidfile){
fscanf(pidfile, "%d", &pid); // read PID of (possibly) running process
fclose(pidfile);
if((name = readname(pid)) && strncmp(name, myname, 255) == 0)
iffound(pid);
}
}
// There is no pidfile or it consists a wrong record
while((de = readdir(dir))){ // scan /proc
if(!(pid = (pid_t)atoi(de->d_name)) || pid == self) // pass non-PID files and self
continue;
if((name = readname(pid)) && strncmp(name, myname, 255) == 0)
iffound(pid);
}
closedir(dir);
if(pidfilename){
pidfile = fopen(pidfilename, "w");
fprintf(pidfile, "%d\n", self); // write self PID to pidfile
fclose(pidfile);
}
}
如果您运行 function check4running
,您将能够保证您的守护进程是单一的:第一个阻塞是锁定自我可执行文件,如果这是不可能的,它会扫描/proc/
并检查 pidfile(如果存在)。