I can't find the way to properly turn on the wi-fi card on my laptop When I turn it on and issue

$ sudo iwconfig wlan0 txpower auto
$ sudo iwlist wlan0 scan
wlan0     Interface doesn't support scanning : Network is down

it reports that the network is down. The attempt to bring it up also fails

$ sudo ifup wlan0
wlan0     no private ioctls.

Failed to bring up wlan0.

Apparently I'm missing some basic low-level iw... command.

When I issue dhclient on the interface.

$ sudo dhclient -v wlan0
Internet Systems Consortium DHCP Client 4.2.2
Copyright 2004-2011 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

^C$

and interrupt it, it brings the device up somehow and then scanning etc. works. I'd like to avoid this obviously superfluous step

Best Answer


sudo ip link set wlan0 up or sudo ifconfig wlan0 up .

Answer from Apr 13'17:

This is an attempt to elaborate on martin's answer

ifup and ifdown commands are part of ifupdown package , which now is considered a legacy frontend for network configuration , compared to newer ones, such as network manager .

Upon ifup ifupdown reads configuration settings from /etc/network/interfaces ; it runs pre-up , post-up and post-down scripts from /etc/network , which include starting /etc/wpasupplicant/ifupdown.sh that processes additional wpa-* configuration options for wpa wifi, in /etc/network/interfaces (see zcat /usr/share/doc/wpasupplicant/README.Debian.gz for documentation). For WEP wireless-tools package plays similar role to wpa-supplicant . iwconfig is from wireless-tools , too.

ifconfig at the same time is a lower level tool , which is used by ifupdown and allows for more flexibility. For instance, there are 6 modes of wifi adapter functioning and IIRC ifupdown covers only managed mode (+ roaming mode, which formally isn't mode?). With iwconfig and ifconfig you can enable e.g. monitor mode of your wireless card, while with ifupdown you won't be able to do that directly.

ip command is a newer tool that works on top of netlink sockets , a new way to configure the kernel network stack from userspace (tools like ifconfig are built on top of ioctl system calls).