无法写入/proc/sys/kernel/ns_last_pid文件 [英] unable to write /proc/sys/kernel/ns_last_pid file

问题描述

我想编辑/proc/sys/kernel 中存在的 ns_last_pid 文件，但出现了只读文件系统.如何解决呢?这就是我为打开文件而写的.

I want to edit the ns_last_pid file present in /proc/sys/kernel, but i'm getting the error of Read-only file system. How to resolve this? This is what i've written to open the file.

int fd = open("/proc/sys/kernel/ns_last_pid", O_RDWR | O_CREAT, 0644);
            if (fd < 0) {
                cout<<strerror(errno)<<"\n";
                return 1;
            }

我要写这个文件，改变它的值.该文件包含一个数字，代表代表分配给任何进程的最后一个pid.我必须对此进行编辑，以便我可以为进程获取所需的pid号.就像这些家伙为他们的项目 CRIU 做的一样(请参见第一个链接).

I've to write this file, change it's value. This file contains a single number represnting the last pid allocated to any process. I've to edit this so that i can get desired pid number for a process. like these guys are doing for their project CRIU(see first link).

Pid_restore (criu.org)，

Pid_restore(criu.org),

如何在Linux中设置进程ID对于特定程序(stackoverflow答案)

How to set process ID in Linux for a specific program(stackoverflow answer)

最小的可复制示例

#include <fstream>
#include <bits/stdc++.h>
#include <sys/types.h>
#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <sched.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <unistd.h>
#include <fcntl.h> 
#include <errno.h>
#include <sys/types.h>
#include <sys/syscall.h>

using namespace std;
    int main(){
            printf("Opening ns_last_pid...\n");   
            int fd = open("/proc/sys/kernel/ns_last_pid", O_RDWR | O_CREAT, 0644);
            if (fd < 0) {
                cout<<strerror(errno)<<"\n";
                return 1;
            }
            printf("Locking ns_last_pid...\n");
            if (flock(fd, LOCK_EX)) {
                close(fd);
                printf("Can't lock ns_last_pid\n");
                return 1;
            }
            printf("Done\n");
            char buf[100];
            int pid_max = 30000;
            snprintf(buf, sizeof(buf), "%d", pid_max-1);

            printf("Writing pid-1 to ns_last_pid...\n");
            cout<<fd<<"\n";
            if (write(fd, buf, strlen(buf)) != strlen(buf)) {
               cout<<strerror(errno)<<"\n";
               printf("Can't write to buf\n");
               return 1;
            }
        
            printf("Done\n");
        
            printf("Cleaning up...");
            if (flock(fd, LOCK_UN)) {
                printf("Can't unlock");
                }
        
            close(fd);
        
            printf("Done\n");            
                      
            return 0;
        }

推荐答案

1. 要更改内核文件的程序，该程序应归root用户所有

1. For a program to change kernel files, it should be owned by root

sudo chown root程序//程序是可执行文件(二进制文件)

sudo chown root program // program is the executable(the binary)

在可执行文件上设置setuid位，以执行具有超级用户访问权限的程序.这样，即使我们以计算机上的任何用户身份执行它，它也将以root用户身份运行.

set the setuid bit on the executable to execute a program with superuser access. with this it will run as root even if we execute it as any user on our machine.

sudo chmod u + s程序

编译源代码并用sudo运行程序，防止其他权限访问错误.

Compile the source code and run the program with sudo to prevent other permission access errors.

感谢 TedLyngmo 提出此解决方案.

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