unshare: what is shared by default?

[abitrolly]

Am I right that by default unshare call just copies existing namespace with all things connected, and runs a new process in it?

[karelzak]

It follows kernel syscall behavior:

man 2 unshare:

       If flags is specified as zero, then unshare() is a no-op; no changes are made to the calling
       process's execution context.

The result is that unshare(1) without any option just executes the shell.