linux c 通过 /proc 获取 pid 进程列表

╰半橙微兮° 2021-09-03 10:45 640阅读 0赞

如果要获取当前正在运行的进程的PID列表，可以使用[`opendir()`][opendir]和[`readdir()`][readdir]打开`/proc`并迭代其中的文件/文件夹列表。然后，您可以检查文件名是数字的文件夹。检查后，您可以打开`/proc/<PID>/stat`以获取所需的信息（尤其是您想要的第12个字段`majflt`）。

这是一个简单的工作示例（可能需要更多错误检查和调整）：

#include <sys/types.h>
    #include <dirent.h>
    #include <stdio.h>
    #include <ctype.h>
    
    // Helper function to check if a struct dirent from /proc is a PID folder.
    int is_pid_folder(const struct dirent *entry) {
        const char *p;
    
        for (p = entry->d_name; *p; p++) {
            if (!isdigit(*p))
                return 0;
        }
    
        return 1;
    }
    
    int main(void) {
        DIR *procdir;
        FILE *fp;
        struct dirent *entry;
        char path[256 + 5 + 5]; // d_name + /proc + /stat
        int pid;
        unsigned long maj_faults;
    
        // Open /proc directory.
        procdir = opendir("/proc");
        if (!procdir) {
            perror("opendir failed");
            return 1;
        }
    
        // Iterate through all files and folders of /proc.
        while ((entry = readdir(procdir))) {
            // Skip anything that is not a PID folder.
            if (!is_pid_folder(entry))
                continue;
    
            // Try to open /proc/<PID>/stat.
            snprintf(path, sizeof(path), "/proc/%s/stat", entry->d_name);
            fp = fopen(path, "r");
    
            if (!fp) {
                perror(path);
                continue;
            }
    
            // Get PID, process name and number of faults.
            fscanf(fp, "%d %s %*c %*d %*d %*d %*d %*d %*u %*lu %*lu %lu",
                &pid, &path, &maj_faults
            );
    
            // Pretty print.
            printf("%5d %-20s: %lu\n", pid, path, maj_faults);
            fclose(fp);
        }
    
        return 0;
    }

样本输出：

1 (systemd)           : 37
    35 (systemd-journal)   : 1
    66 (systemd-udevd)     : 2
    91 (dbus-daemon)       : 4
    95 (systemd-logind)    : 1
    13 (dhclient)          : 2
    43 (unattended-upgr)   : 10
    48 (containerd)        : 11
    51 (agetty)            : 1
    ..

[opendir]: https://man7.org/linux/man-pages/man3/opendir.3.html
[readdir]: https://www.man7.org/linux/man-pages/man3/readdir.3.html