# UTS Namespace
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## Basic Information A UTS (UNIX Time-Sharing System) namespace is a Linux kernel feature that provides i**solation of two system identifiers**: the **hostname** and the **NIS** (Network Information Service) domain name. This isolation allows each UTS namespace to have its **own independent hostname and NIS domain name**, which is particularly useful in containerization scenarios where each container should appear as a separate system with its own hostname. ### How it works: 1. When a new UTS namespace is created, it starts with a **copy of the hostname and NIS domain name from its parent namespace**. This means that, at creation, the new namespace s**hares the same identifiers as its parent**. However, any subsequent changes to the hostname or NIS domain name within the namespace will not affect other namespaces. 2. Processes within a UTS namespace **can change the hostname and NIS domain name** using the `sethostname()` and `setdomainname()` system calls, respectively. These changes are local to the namespace and do not affect other namespaces or the host system. 3. Processes can move between namespaces using the `setns()` system call or create new namespaces using the `unshare()` or `clone()` system calls with the `CLONE_NEWUTS` flag. When a process moves to a new namespace or creates one, it will start using the hostname and NIS domain name associated with that namespace. ## Lab: ### Create different Namespaces #### CLI ```bash sudo unshare -u [--mount-proc] /bin/bash ``` By mounting a new instance of the `/proc` filesystem if you use the param `--mount-proc`, you ensure that the new mount namespace has an **accurate and isolated view of the process information specific to that namespace**.
Error: bash: fork: Cannot allocate memory If you run the previous line without `-f` you will get that error.\ The error is caused by the PID 1 process exits in the new namespace. After bash start to run, bash will fork several new sub-processes to do somethings. If you run unshare without -f, bash will have the same pid as the current "unshare" process. The current "unshare" process call the unshare systemcall, create a new pid namespace, but the current "unshare" process is not in the new pid namespace. It is the desired behavior of linux kernel: process A creates a new namespace, the process A itself won't be put into the new namespace, only the sub-processes of process A will be put into the new namespace. So when you run: ``` unshare -p /bin/bash ``` The unshare process will exec /bin/bash, and /bin/bash forks several sub-processes, the first sub-process of bash will become PID 1 of the new namespace, and the subprocess will exit after it completes its job. So the PID 1 of the new namespace exits. The PID 1 process has a special function: it should become all the orphan processes' parent process. If PID 1 process in the root namespace exits, kernel will panic. If PID 1 process in a sub namespace exits, linux kernel will call the disable\_pid\_allocation function, which will clean the PIDNS\_HASH\_ADDING flag in that namespace. When linux kernel create a new process, kernel will call alloc\_pid function to allocate a PID in a namespace, and if the PIDNS\_HASH\_ADDING flag is not set, alloc\_pid function will return a -ENOMEM error. That's why you got the "Cannot allocate memory" error. You can resolve this issue by use the '-f' option: ``` unshare -fp /bin/bash ``` If you run unshare with '-f' option, unshare will fork a new process after it create the new pid namespace. And run /bin/bash in the new process. The new process will be the pid 1 of the new pid namespace. Then bash will also fork several sub-processes to do some jobs. As bash itself is the pid 1 of the new pid namespace, its sub-processes can exit without any problem. Copied from [https://stackoverflow.com/questions/44666700/unshare-pid-bin-bash-fork-cannot-allocate-memory](https://stackoverflow.com/questions/44666700/unshare-pid-bin-bash-fork-cannot-allocate-memory)
#### Docker ```bash docker run -ti --name ubuntu1 -v /usr:/ubuntu1 ubuntu bash ``` ### Check which namespace is your process in ```bash ls -l /proc/self/ns/uts lrwxrwxrwx 1 root root 0 Apr 4 20:49 /proc/self/ns/uts -> 'uts:[4026531838]' ``` ### Find all UTS namespaces {% code overflow="wrap" %} ```bash sudo find /proc -maxdepth 3 -type l -name uts -exec readlink {} \; 2>/dev/null | sort -u # Find the processes with an specific namespace sudo find /proc -maxdepth 3 -type l -name uts -exec ls -l {} \; 2>/dev/null | grep ``` {% endcode %} ### Enter inside an UTS namespace ```bash nsenter -u TARGET_PID --pid /bin/bash ``` Also, you can only **enter in another process namespace if you are root**. And you **cannot** **enter** in other namespace **without a descriptor** pointing to it (like `/proc/self/ns/uts`). ### Change hostname ```bash unshare -u /bin/bash hostname newhostname # Hostname won't be changed inside the host UTS ns ```
Learn AWS hacking from zero to hero with htARTE (HackTricks AWS Red Team Expert)! Other ways to support HackTricks: * If you want to see your **company advertised in HackTricks** or **download HackTricks in PDF** Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)! * Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com) * Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family) * **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** 🐦 [**@carlospolopm**](https://twitter.com/carlospolopm)**.** * **Share your hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.