Install as unprivileged user on OpenWrt

[aaaaalbert]

The current OpenWrt installer (in the form of @XuefengHuang's .ipk) will install Seattle as the root user. We should provide an option to use a non-privileged account if the user has (or is willing to install) the required tools such as useradd. See the OpenWrt docs for details: http://wiki.openwrt.org/doc/howto/secure.access

[XuefengHuang]

I tested it on router as non-root user. Creating new user, accessing to router as non-privileged account, installing... I noticed that opkg only works as root user. So the solution is using sudo when installing Seattle as non-root user.