利用setns()将进程加入一个新的network namespace

root@ubuntu:/home/ubuntu# docker run -itd --name test ubuntu /bin/bash
86d1bf0df1c9ff0a705be14b5263473f5c2d2bbbcc01b7159494047d74a51647
root@ubuntu:/home/ubuntu# docker ps | grep 86d1bf0df1c9
86d1bf0df1c9        ubuntu              "/bin/bash"         19 seconds ago      Up 18 seconds                           test
root@ubuntu:/home/ubuntu# docker inspect --format '{{ .State.Pid }}' test
58831

#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
 
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE);
                        } while (0)
 
int
main(int argc, char *argv[]) {
        int fd;
 
        if (argc < 3) {
                fprintf(stderr, "%s /proc/PID/ns/FILE cmd args...
", argv[0]);
                exit(EXIT_FAILURE);
        }
 
        fd = open(argv[1], O_RDONLY);   // Get descriptor for namespace
        if (fd == -1)
                errExit("open");
 
        if (setns(fd, 0) == -1)         // Join that namespace
                errExit("setns");
 
        execvp(argv[2], &argv[2]);      // Execute a command in namspace
        errExit("execvp");
}

root@ubuntu:/home/ubuntu/test# ./ns  /proc/58831/ns/net /bin/bash
root@ubuntu:/home/ubuntu/test# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
386: eth0@if387: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:ac:11:00:04 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 172.17.0.4/16 brd 172.17.255.255 scope global eth0
       valid_lft forever preferred_lft forever
root@ubuntu:/home/ubuntu/test# 

root@ubuntu:/home/ubuntu/test# ls -l /proc/58831/ns/net
lrwxrwxrwx 1 root root 0 Nov 24 15:54 /proc/58831/ns/net -> 'net:[4026534375]'
root@ubuntu:/home/ubuntu/test# ls -l /proc/59899/ns/net
lrwxrwxrwx 1 root root 0 Nov 24 16:03 /proc/59899/ns/net -> 'net:[4026534375]'
root@ubuntu:/home/ubuntu/test# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
386: eth0@if387: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether 02:42:ac:11:00:04 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 172.17.0.4/16 brd 172.17.255.255 scope global eth0
       valid_lft forever preferred_lft forever
root@ubuntu:/home/ubuntu/test#