Put bash process in new other namespaces

unshare --pid --net --fork --mount-proc /bin/bash

Now, in this shell - list the running the processes, you can see that bash is in another PID namespace:

# ps aux
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.0   7100  3656 pts/0    S    19:27   0:00 /bin/bash
root           2  0.0  0.0   9700  3360 pts/0    R+   19:27   0:00 ps aux

Show network parameters - you can see, the bash process is in another network namespace:

# ip a
1: lo:  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