+++
date    = "2025-03-05T18:11:13+00:00"
lastmod = "2025-03-05T18:11:13+00:00"
tags    = [ "gists", "linux" ]
+++

There's a [quick](/tdro/messages/unshare/#tdro-messages-unshare) way to test the
offline behaviour of programs on Linux.

```shell{ caption="Run bash in a new network [namespace](https://www.man7.org/linux/man-pages/man1/unshare.1.html)" }
unshare -c -n bash
```
{{< disclose >}}
Then only loopback is available.
{{</ disclose >}}

```shell
$ ip addr
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
```

List network namespaces with [`lsns`](https://www.man7.org/linux/man-pages/man8/lsns.8.html).

```shell
$ lsns -t net
NS  TYPE NPROCS PID   USER  NETNSID    COMMAND
999 net  2      111   user  3          systemd
888 net  1      222   user  unassigned └─bash
```