unshare --pid /bin/bash - fork cannot allocate memory

Question

I\'m experimenting with linux namespaces. Specifically the pid namespace.

I thought I\'d test something out with bash but run into this problem:

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Answer 1

This does not explain why this happens, but shows how to correctly launch a shell in a new pid namespace:

Use the -f flag to fork off the shell from unshare:

unshare -fp /bin/bash

You also need to pass the --mount-proc option to ensure that the shell will get PID 1 in the newly created namespace:

unshare -fp --mount-proc /bin/bash

Now run ps:

# ps
   PID TTY          TIME CMD
 1 pts/1    00:00:00 bash
11 pts/1    00:00:00 ps