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Let’s look at processes running in Container ubuntu1:
```
root@3a1bf12161c9:/# ps
PID TTY TIME CMD
1 ? 00:00:00 bash
15 ? 00:00:00 ps
```
Let’s look at processes running in Container ubuntu2:
```
root@8beb85abe6a5:/# ps
PID TTY TIME CMD
1 ? 00:00:00 bash
14 ? 00:00:00 ps
```
Let’s look at the 2 “bash” process in host machine:
```
$ ps -eaf|grep root | grep bash
root 5413 1697 0 05:54 pts/28 00:00:00 bash
root 5516 1697 0 05:54 pts/31 00:00:00 bash
```
bash process in Container1 and Container2 have the same PID 1 since they have their own process namespace. The same bash process shows up in host machine as a different pid.
Let’s look at the root directory content in Container ubuntu1:
```
root@3a1bf12161c9:/# ls /
bin dev home lib64 mnt proc run srv tmp usr
boot etc lib media opt root sbin sys ubuntu1 var
```
Let’s look at the root directory content in Container ubuntu2:
```
root@8beb85abe6a5:/# ls /
bin dev home lib64 mnt proc run srv tmp usr
boot etc lib media opt root sbin sys ubuntu2 var
```
As we can see above, each Container has its own filesystem and we can see “/usr” from host machine mounted as “/ubuntu1” in Container1 and as “/ubuntu2” in Container2.
User namespaces are available from Linux kernel versions > 3.8. With User namespace, **userid and groupid in a namespace is different from host machine’s userid and groupid** for the same user and group. When Docker Containers use User namespace, each **container gets their own userid and groupid**. For example, **root** user **inside****Container** is **not** root **inside****host****machine**. This provides greater security. In case the Container gets compromised and the hacker gets root access inside Container, the hacker still cannot break inside the host machine since the root user inside the Container is not root inside the host machine. Docker introduced support for user namespace in version 1.10.\
To use user namespace, Docker daemon needs to be started with **`--userns-remap=default`**(In ubuntu 14.04, this can be done by modifying `/etc/default/docker` and then executing `sudo service docker restart`)\
Let’s start a ubuntu Container and look at its UID and GID:
```
root@3a1bf12161c9:/# id
uid=0(root) gid=0(root) groups=0(root)
```
To find the UID associated with the root UID inside Container, we need to first find the PID in host machine for the Container process and get the associated UID.\
Following output shows the “bash” PID in host machine for the Container:
```
231072 8955 8207 0 21:23 pts/14 00:00:00 bash
```
Let’s look at the associated UID for PID 8955:
```
smakam14@jungle1:/usr$ cat /proc/8955/uid_map
0 231072 65536
```
As we can see above, userid 0(root) in container 1 is mapped to userid 231072 in host machine.\
In the current Docker user namespace implementation, UID and GID mapping happens at Docker daemon level. There is work ongoing to allow the mappings to be done at Container level so that multi-tenant support is possible.
Each cgroup namespace has its **own set of cgroup root directories**. These root directories are the base points for the relative locations displayed in the corresponding records in the `/proc/[pid]/cgroup` file. When a process creates a new cgroup namespace using clone(2) or unshare(2) with the CLONE\_NEWCGROUP flag, its current cgroups directories become the cgroup root directories of the new namespace. (This applies both for the cgroups version 1 hierarchies and the cgroups version 2 unified hierarchy.)
<summary><strong>Support HackTricks and get benefits!</strong></summary>
Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
