xx@xx:~$./userns -U -M '0 100000 65536' -G '0 100000 65535' bash
ERROR: write /proc/414325/uid_map: Operation not permitted
But use "./userns -U -M '0 100000 65536' -G '0 100000 1' bash " there not have error.why the length of range greater than 1 will occur error.
os: ubuntu sources code of userns: userns