程序在启动时将pid写入文件，当程序再次启动时会进行检测，避免启动多个实例。

util-pidfile.h文件

#ifndef __UTIL_PID_H__
#define __UTIL_PID_H__

int PidfileCreate(const char *);
void PidfileRemove(const char *);
int PidfileTestRunning(const char *pid_filename);

#endif /* __UTIL_PID_H__ */

util-pidfile.c文件

#include <stdio.h>
#include <inttypes.h>   // PRIuMAX
#include <errno.h>      // errno
#include <string.h>     // strerror

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h> // getpid
#include <signal.h> // kill

#include "util-debug.h"
#include "util-pidfile.h"

/**
 * \brief Write a pid file (used at the startup)
 *        This commonly needed by the init scripts
 *
 * \param pointer to the name of the pid file to write (optarg)
 *
 * \retval 0 if succes
 * \retval -1 on failure
 */
int PidfileCreate(const char *pidfile)
{
    int pidfd = 0;
    char val[16];

    int len = snprintf(val, sizeof(val), "%"PRIuMAX"\n", (uintmax_t)getpid());
    if (len <= 0) {
        LogError("Pid error (%s)", strerror(errno));
        return(-1);
    }

    pidfd = open(pidfile, O_CREAT | O_TRUNC | O_NOFOLLOW | O_WRONLY, 0644);
    if (pidfd < 0) {
        LogError("unable to set pidfile '%s': %s",
                   pidfile,
                   strerror(errno));
        return(-1);
    }

    ssize_t r = write(pidfd, val, (unsigned int)len);
    if (r == -1) {
        LogError("unable to write pidfile: %s", strerror(errno));
        close(pidfd);
        return(-1);
    } else if ((size_t)r != len) {
        LogError("unable to write pidfile: wrote"
                " %"PRIdMAX" of %"PRIuMAX" bytes.", (intmax_t)r, (uintmax_t)len);
        close(pidfd);
        return(-1);
    }

    close(pidfd);
    return(0);
}

/**
 * \brief Remove the pid file (used at the startup)
 *
 * \param pointer to the name of the pid file to write (optarg)
 */
void PidfileRemove(const char *pid_filename)
{
    if (pid_filename != NULL) {
        /* we ignore the result, the user may have removed the file already. */
        (void)unlink(pid_filename);
    }
}

/**
 * \brief Check a pid file (used at the startup)
 *        This commonly needed by the init scripts
 *
 * \param pointer to the name of the pid file to write (optarg)
 *
 * \retval 0 if succes
 * \retval -1 on failure
 */
int PidfileTestRunning(const char *pid_filename)
{
    if (access(pid_filename, F_OK) == 0) {
        /* Check if the existing process is still alive. */
        pid_t pidv;
        FILE *pf;

        pf = fopen(pid_filename, "r");
        if (pf == NULL) {
            LogError("pid file '%s' exists and can not be read. Aborting!",
                    pid_filename);
            return -1;
        }

        if (fscanf(pf, "%d", &pidv) == 1 && kill(pidv, 0) == 0) {
            fclose(pf);
            LogError("pid file '%s' exists. Is program already running? Aborting!",
                    pid_filename);
            return -1;
        }

        fclose(pf);
    }
    return 0;
}

util-debug.h日志打印（主要是为了方便以后使用其他打印接口，就不用再修改util-pidfile.c文件了）

#ifndef __UTIL_DEBUG_H__
#define __UTIL_DEBUG_H__

#ifndef LOG_PRINT
#define LOG_MAX_LOG_MSG_LEN 2048
#define Log(x, file, func, line, ...)                           \
    do {                                                        \
        char _log_msg[LOG_MAX_LOG_MSG_LEN];                     \
        snprintf(_log_msg, LOG_MAX_LOG_MSG_LEN, __VA_ARGS__);   \
        fprintf(stdout, "<%s> %s\n", x, _log_msg);              \
    } while(0)

#define LogError(...) Log("ERROR", \
        __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)

#define LogWarning(...) Log("WARNING", \
        __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)

#define LogInfo(...) Log("INFO", \
        __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)

#define LogDebug(...) Log("DEBUG", \
        __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)

#define FatalError(...) do {                                           \
    LogError(__VA_ARGS__);                                             \
    exit(EXIT_FAILURE);                                                \
} while(0)
#endif

#endif //__UTIL_DEBUG_H__

main.c文件

#include <stdio.h>
#include <unistd.h>

#include "util-pidfile.h"

int main()
{
    int result = 0;

    const char *pidfile = "/var/run/test_pid01.pid";

    if (PidfileTestRunning(pidfile) != 0)
        return -1;

    PidfileCreate(pidfile);

    while (1){
        sleep(1);
    }

    PidfileRemove(pidfile);
    return 0;
}

编译完成后运行该程序，然后再启动一个终端，再次运行这个程序的时候就会打印程序已运行并退出。

<ERROR> pid file '/var/run/test_pid01.pid' exists. Is program already running? Aborting!