I have an ssh connection to a linux machine which is hibernated after some non-activity time.
I want to make it resume, how do I do that?
(writing to /dev/mouse to simulate mouse movement didn't do the trick)
A machine that is hibernating cannot come out of sleep without pressing the power button, or sending a magic packet if the ethernet adaptor has Wake On Lan (WOL) capability and the motherboard supports that. WOL packets can only be generated on the local network, not remotely from other networks.
-Adam
In addition to what Adam has stated, some motherboards support waking from various states when an interrupt is triggered.
The key here is which state you are referring to as hibernation; are you talking about an extremely low-power mode in hardware, or software hibernation where core memory is written to disk and the machine is turned off completely? If the latter, WOL is the only possibility; if the former, than you can tell your motherboard to watch for interrupts from various sources and you can use some other means to trigger a wake-up.
A good starting point for reading is the Wake-On-LAN article on Wikipedia.
To accomplish WOL you need a few things:
First, check the BIOS of the machine you're waking to see if it supports WOL. If it does, make sure it's turned on.
Then get a program that can send WOL packets:
In linux: sudo apt-get install wakeonlan
For windows just find one to download using google. There are probably 100 different apps that do it, I don't use Windows so I don't have one to reference.
If you want to receive WOL packets from outside of your local network. Configure your router to forward port 9 to 255.255.255.255 (IP Broadcast-To-All address).
For some really useful info on the WOL protocol as well as a sample capture file that can be loaded in wireshark, see this article.
Related
Environment:
I have an embedded linux system running with an ARM based iMX7 processor. It runs on a build from yocto linux which is very much based on Fedora.
Scenario:
My system uses Suspend To RAM feature which is linux system power saving mode that is explained quite well in this link. This is done to save power at a certain stage.
Objective:
Now, I need to keep the wifi link open during this stage. And as I read from some discussions like this, it seems to be possible to do so.
How can I do this?
Read up on similar discussions:
Reading through this discussion, it explains how to do this on a intel based desktop linux computer. But I don't have the /etc/NetworkManager on my embedded linux device. Probably there is a different way to do it on a Fedora based embdded linux system.
Can I get some suggestions on how to do this or even how to approach this?
None of the articles you quoted even suggest that it is possible to leave WiFi on - in fact one of them says it can't be done. All they provide is various tricks to make the wake-up faster.
Depends on the hardware but very likely, leaving it on is really impossible. Suspend-to-ram includes a hardware command that switches the CPU clock off, places its interconnect buses into idle state, and disables main power to all the peripherals (leaving only standby power to those peripherals that support standby mode).
I don't know if your WiFi device has support for running on standby power nor whether the embedded hardware you have has the ability to provide that power to it while the CPU is off. If that ability exists, it will likely be accessible as a kernel driver parameter.
You may be able to save some startup time when waking up from standby by providing a static configuration for your WiFi device rather than using the default automatic connection (which involves searching for a router to connect to, obtaining an IP address, etc.).
You can't just keep wifi active during sleep/resume. You can optimise reconnection speed but I believe NM and connman both do that already.
I'm searching for help and an opinion-advice for a network project, in which I'm working lately. This requires a Linux machine to be a passive network appliance.
Network packets come in from one network interface and come out from another interface ( net--eth0-->Linux PC--eth1-->net) without making any modifications on data.
The application, which is going to run on the Linux system, will change only the order of the packets. It is going to be a "silly" network emulator application.
The first implementation was made with RAW sockets, where read() is called every time a packet arrives to user space and write() is called when an Ethernet packet should be sent down to the NIC.
I would like to know if there is a more practical and direct way than RAW sockets, bypassing Linux's network stack.
If what you want is to bypass the kernel, DPDK in Linux and NetMap in FreeBSD are options to do just that.
Indeed this can be done in dpdk in Linux. There are l3fw and l2fwd sample applications in the examples folder of the dpdk tree, which may inspire you. Also consider using vpp, a fd.io project hosted by Linux Foundation, which can use dpdk.
Rami Rosen
I'm attempting to get kernel debugging to work during boot. I've followed all the steps to install it (how to use kgdb over ethernet(kgdboe)?) and can connect fine when I insmod after loading, but if I add this
BOOT_IMAGE=/vmlinuz-4.0.0-rc7+ root=UUID=<my_root> ro drm.debug=0x04 kgdbwait kgdboe=#<src_ip>/eth1,#<target_ip>/ vt.handoff=7
to the kernel boot line, I don't see the module loaded, and it doesn't kgdbwait.
When I look at my kern.log, I see the following:
kgdboe: eth0 does not have a in_ifaddr struct associated. Cannot get default IP address.
I have both eth0 and eth1 by the way, but only eth1 is connected.
Any suggestions? Is it just that the pcie network card isn't loaded until after boot and it's causing me issues?
Also, why would I need to specify the source or target ip addresses? Is there any way to have kgdboe accept all ip addresses, even when trying to load it at boot?
Thanks
Yes, for early kernel debug kgdboe does not really work. There are several issues, some easy to solve, some not solveable. You can hard link the required modules rather than demand load them to solve the easy issue. But the core problem is that the kgdb early wait will pause all worker threads, and nearly all of the Ethernet PCIe card drivers require worker threads, or else require IRQs. Even on the polled Ethernet driver support (very limited), the IRQ's can be preempted (or illegally hold locks), and prevent the polled Ethernet driver from functioning. As a result early kernel debug does not function with kgdboe reliably, and with some Ethernet drivers, at all. (e.g. kgdbwait on the GRUB2 boot line.) There has been occasional talk about hacking up various Ethernet driver sources to attempt to provide kgdboe support over a special purpose Ethernet driver, but none that I know of that is distributed. You are still best off with using a serial port, and for full functionality, a serial console, which can be multiplexed onto a single serial port if need be with kgdboc (agent-proxy). If true remote access is required, then remote into the debugging system that initiates the serial connection.
You can also use the USB port, but requires a specific USB<->serial USB dongle that is no longer sold. (Ajays Blue dongle). These were discontinued about 6 months ago, and there is no replacement yet. (It was a Windows debugging device adapted to Linux, and Windows has moved on to native USB3.0 debugging features, and Linux has yet to catch up to that.) So, unless you have the needed USB converter, or have another source, or have an alternative adapter, you are out of luck on USB2.0.
Serial is still your best option, sadly, even in 2016.
See: http://kdbg.wiki.kernel.org
I am writing a linux kernel module for some tunnelling activity. The module will get packets from the networking stack and perform some operations on it. What is the best possible way to inject packets into the stack from the bottom(emulate ethernet packet arrival on wire) so that the packet traverses the entire receive path and is delivered to my module.
My module uses the kernel br_handle_frame_hook hook to get the packet which means that it cannot co-reside with the linux native bridge module. Any ideas will be appreciated.
Consider using NetFilter
http://www.phrack.org/issues.html?issue=61&id=13
TAP would be great, if you're working in user space, which you're not
I believe that TAP device is what you are looking for - a nice way to send/receive Ethernet packets from user-space
I recommend tap like #raber before me. I also recommend reading this excelet tutorial: http://backreference.org/2010/03/26/tuntap-interface-tutorial/ .
You asked whether you can make the tap non-programatically and then replay traffic into it. The answer is yes. Look for the 'persistency' options (which b.t.w. can also be done programatically with a short tool you can write yourself if you prefer not to download tools that can already do it). You may also want/need to define the user that may use the tap (or otherwise just sudo your operations).
I have tried using several commands as well as couple of examples using C/C++ but am still not able to find a flawless method that can differentiate between physical or virtual ethernet adapters. Physical means, on that available on your board or installed externally and virtual means created by virtualization apps such as VirtualBox/VMWare/Virtual PC or VPN etc.
Any pointers?
There is no flawless method. A virtual adapter can have any MAC address, including one that might have been assigned by a constructor to a physical device. And the other way around, given that one can change the MAC address of a physical adapter. You can only make an educated guess.
You might find it easier to detect if you are running virtualized at all, rather than look for specific information about the NICs. The virt-what(1) tool looks through aspects of the running system to guess if the system is virtualized or not. (The script isn't as smart as you think, but it does have a lot of small information gathering tools in one place.)
Someone intentionally trying to bypass a license check would probably not find it difficult to defeat this mechanism.
Maybe one can use mii-tool and check if it fails, which it does for virtual:
mii-tool vmbr2
SIOCGMIIPHY on 'vmbr2' failed: Operation not supported
mii-tool eno1
eno1: negotiated 1000baseT-FD flow-control, link ok
EDIT:
What is mii-tool: view, manipulate media-independent interface status
This utility checks or sets the status of a network interface's
Media Independent Interface (MII) unit. Most fast ethernet
adapters use an MII to autonegotiate link speed and duplex
setting.
https://www.man7.org/linux/man-pages/man8/mii-tool.8.html