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by gdt
Tue Feb 12, 2019 6:00 pm
Forum: Beginners
Topic: RPi3B+ and watchdog...
Replies: 14
Views: 10203

Re: RPi3B+ and watchdog...

The watchdog and random number generator seem to be built into the kernel in recent Raspbian (eg, Linux kernel build 4.14.79-v7+ #1159) , so no module needs to be loaded.

Simply edit /etc/systemd/system.conf to include "RuntimeWatchdogSec=14".
by gdt
Thu Jan 04, 2018 1:29 pm
Forum: General discussion
Topic: Chip architecture - is the Pi vulnerable?
Replies: 55
Views: 8602

Re: Chip architecture - is the Pi vulnerable?

I think exploits of these classes will disappear completely in CPUs in the next architectural cycle That's probably a little too optimistic. This class of problems -- microarchitectural side channel attacks -- have been known since 2005 [1] but used as attacks on cryptography systems. The introduct...
by gdt
Thu Mar 30, 2017 11:45 am
Forum: Networking and servers
Topic: Pi almost entirely unable to run WordPress site
Replies: 7
Views: 2753

Re: Pi almost entirely unable to run WordPress site

Apache, even on the original RPi, serves static web pages just fine. The problem comes with large-footprint databases needed for storing the Wordpress data. You must tune MySQL for the small amount of RAM available: there is guidance in this forum. Getting the data off SD card and onto faster USB-at...
by gdt
Thu Mar 30, 2017 11:23 am
Forum: Networking and servers
Topic: How to display the MAC / IP addresses
Replies: 8
Views: 1473

Re: How to display the MAC / IP addresses

You can display the ethernet addresses of machines which connect to your from the same subnet your RPi is on. Use the "arp" command, the "ip neigh show" command, or display the file /proc/net/arp. For IPv6 try "ip -6 neigh show". All these options list the "neighbour cache", which we used to call th...
by gdt
Thu May 12, 2016 7:21 am
Forum: Other projects
Topic: Rackmount mounting
Replies: 2
Views: 17872

Rackmount mounting

The low power used by the RPi3 makes it attractive for some telecommunications tasks. We are having trouble finding a mounting or case for one or more RPi3s which would fit in a 19in rack. In the worst case we'll use a shelf, but a more secure mounting would be very appreciated as then we could run ...
by gdt
Tue Mar 29, 2016 10:46 am
Forum: Networking and servers
Topic: Give a Static IP if no Dynamic IP
Replies: 2
Views: 701

Re: Give a Static IP if no Dynamic IP

If you intend to do this for a lot of machines (say a whole classroom) then your need might be better met with a link-local address and a ZeroConf mDNS advertisement. 1) The easiest way to get a link local address is to activate IPv6. Remove the blacklisting in /etc/modprobe.d/ipv6.conf and reboot. ...
by gdt
Thu Mar 24, 2016 1:57 pm
Forum: Networking and servers
Topic: Communication without Internet
Replies: 29
Views: 11669

Re: Communication without Internet

I want to setup the WiFi on my raspberry pi. My raspberry pi is enclosed in a device. In that case you want to implement "WiFi Protected Setup" on your device. Use one of the GPIO pins to connect to a button marked with the "WPS" logo. When you see that button press then instruct wpa_supplicant to ...
by gdt
Thu Mar 24, 2016 1:33 pm
Forum: Networking and servers
Topic: remote access from laptop using ethernet cable
Replies: 1
Views: 498

Re: remote access from laptop using ethernet cable

/etc/network/interfaces with this phrase auto eth0 iface eth0 inet static address 192.168.1.201 netmask 255.255.255.0 gateway 192.168.1.1 is pretty much right. Noting that some large offices will configure their ethernet switching to reject packets from ports where there was no DHCP observed; let's ...
by gdt
Thu Mar 24, 2016 1:14 pm
Forum: Networking and servers
Topic: Raspberry Pi 3 and wlan0 no longer showing up
Replies: 2
Views: 3030

Re: Raspberry Pi 3 and wlan0 no longer showing up

If you've previously run Wheezy on that image then you might still have a /etc/udev/rules.d/70-persistent-net.rules which is claiming the wlan0 name. Edit or delete that file. Jessie works pretty much as described in this proposal . If might be worth booting Jessie with "net.ifnames=1" appended to /...
by gdt
Fri Aug 14, 2015 11:35 am
Forum: Networking and servers
Topic: Networking PIs in school, is the following correct?
Replies: 9
Views: 1527

Re: Networking PIs in school, is the following correct?

If you want to do something in the meantime you could use IPv6 Link Local networking. To activate IPv6 delete the file /etc/modprobe.d/ipv6.conf and reboot. The computer will acquire a IPv6 Link Local address with no configuration of the network required. You can now SSH from one nearby machine to a...
by gdt
Wed Jul 15, 2015 7:11 am
Forum: General discussion
Topic: Raspbian Jessie
Replies: 26
Views: 6944

Re: Raspbian Jessie

I'm not as negative as you. I've got Raspbian Jessie and ARM Jessie happily running on RPi2. There's some stuff which doesn't work (the RPi audio mixer, but the standard LXDE one works fine anyway), and some stuff I recompiled for a better experience (gst-omx, vlc), and some stuff I had to massively...
by gdt
Thu Jun 11, 2015 1:27 pm
Forum: Raspbian
Topic: jessie added to main raspbian archive
Replies: 56
Views: 89489

Re: jessie added to main raspbian archive

Some notes I made upgrading a Raspberry Pi2 from Raspbian Wheezy to Raspbian Jessie. The notes are particularly strong on solving post-upgrade issues which prevent successful boot (udev rules, ifplugd, cgroups, systemd-stub, etc). Enjoy.
by gdt
Tue May 26, 2015 4:10 am
Forum: General discussion
Topic: Any way of verifying Pi is original?
Replies: 30
Views: 11155

Re: Any way of verifying Pi is original?

I think the reader has a valid concern. It certainly wouldn't be difficult to pass off a RPi Model B+ as a RPi2 Model B at a glance. The PCB markings above the raspberry logo are "Raspberry Pi Model B+" and "Raspberry Pi 2 Model B" respectively.
by gdt
Sun May 10, 2015 1:33 pm
Forum: Networking and servers
Topic: Raspberry MRTG limitation
Replies: 2
Views: 1803

Re: Raspberry MRTG limitation

You're asking a capacity planning question. So let's talk capacity. The RPi runs 4 cores at 50-odd MIPS. A modern server will be well north of 4,000 MIPS per core. The RPi has a disk bandwidth to the SD card of about 10MB/s. A modern disk will be well north of 200MB/s. Now this only matters if CPU o...
by gdt
Sat Apr 25, 2015 12:26 pm
Forum: Networking and servers
Topic: RPi WiFi to eth0 bridge not working
Replies: 6
Views: 3330

Re: RPi WiFi to eth0 bridge not working

A few questions you might want to consider: - are the packets forwarding between eth0 and wlan0 using bridging, routing or NAT? - How do devices deeper in the network discover this forwarding device? - is the wlan0 interface a client interface or an access point? - what device in each subnet is resp...
by gdt
Sun Nov 02, 2014 9:33 am
Forum: Networking and servers
Topic: Proposal: RPI CM Supercomputer/HA Architecture
Replies: 5
Views: 1557

Re: Proposal: RPI CM Supercomputer/HA Architecture

The Raspberry Pi does about 380 million floating point operations per second. A server processor purchased with supercomputing in mind will do about 400,000 MFLOPS. So to be competitive with a single server of a typical supercomputer cluster you'll need over a thousand Raspberry Pis. A single rack o...
by gdt
Sun Nov 02, 2014 9:13 am
Forum: Networking and servers
Topic: Simultaneous FTP and OpenVPN - will the Pi cope?
Replies: 2
Views: 1820

Re: Simultaneous FTP and OpenVPN - will the Pi cope?

This is a capacity planning question, and they usually come down to throughput through bottlenecks. The RPi has a number of bottlenecks. The specifications for those are: the CPU, about 700MIPS, 380MFLOPS the RAM, about 400MB free for applications the USB 2.0 bus, which connects the USB ports and th...
by gdt
Tue Oct 21, 2014 11:44 am
Forum: Networking and servers
Topic: Monitoring PI services with SNMP?
Replies: 7
Views: 4726

Re: Monitoring PI services with SNMP?

Net-SNMP exposes the UNIX process table in a MIB. It will also run arbitrary commands for you to check service availability (as opposed to process run state). I tried using collectd in my Pi, but it's too heavy and steals too many resources from the running service to be useful. So Net-SNMP feels li...
by gdt
Sat Oct 18, 2014 10:28 am
Forum: General discussion
Topic: How to store copy of any stdout and/or stderr output
Replies: 4
Views: 930

Re: How to store copy of any stdout and/or stderr output

If you are talking about the platform then look at the output of "dmesg" and the contents of /var/log/syslog and /var/log/daemon. If it is a particular program you are interested in then run it like so: myprogram >file.txt 2>&1 You read pipes and redirections from right to left, so this outputs chan...
by gdt
Sat Oct 18, 2014 10:17 am
Forum: General discussion
Topic: How can I find if software is installed?
Replies: 8
Views: 2400

Re: How can I find if software is installed?

For future reference, you can search the list of all available packages with [email protected] ~ $ apt-cache search pptp bcrelay - Broadcast relay daemon gosa-plugin-pptp - pptp plugin for GOsa² gosa-plugin-pptp-schema - LDAP schema for GOsa² pptp plugin kvpnc - vpn clients frontend for KDE4 network-ma...
by gdt
Sat Oct 18, 2014 8:47 am
Forum: Networking and servers
Topic: Too little RAM?
Replies: 16
Views: 2769

Re: Too little RAM?

You are asking a question about capacity planning for RAM. There's a great script for this: ps_mem.py . I am running Apache and a Postfix mail server (with spam and virus checking). All that fits comfortably into 512MB, with the clamav virus scanner taking up by far the largest amount of RAM (240MB)...
by gdt
Sun Oct 05, 2014 2:08 am
Forum: Networking and servers
Topic: musing on ethernet hardware
Replies: 5
Views: 1262

Re: musing on ethernet hardware

Oh, I meant to add. I am happily using a RPi as a "OpenDaylight" OpenFlow controller to a handful of 10port 10GBase-SPF+ switches. So your idea not only has merit, but works in practice. The RPi is a good choice for experimenting with this sort of thing as issues aren't hidden by the abundant CPU an...
by gdt
Sun Oct 05, 2014 2:00 am
Forum: Networking and servers
Topic: musing on ethernet hardware
Replies: 5
Views: 1262

Re: musing on ethernet hardware

What you are talking about is using the Pi to maintain the TCAM forwarding hardware on a switch's chipset. The 100Mbps connection is an issue for that, as the CPU still has to handle all "extraordinary" traffic. This would include the BPDUs on a switch and the ICMP and maybe even IPv4 fragmentation ...
by gdt
Sun Oct 05, 2014 1:50 am
Forum: General discussion
Topic: Minimal Raspbian install
Replies: 6
Views: 1416

Re: Minimal Raspbian install

Create a new boot target in the init system, and start only the stuff you need. This works better than stripping out the packages, as then if you want to do some debugging (eg, and needing a network to do that) then you can simply do a full boot. This has been done since the earliest production Unix...
by gdt
Wed Sep 10, 2014 11:12 am
Forum: Networking and servers
Topic: How to retrieve bind9 statistics
Replies: 1
Views: 580

Re: How to retrieve bind9 statistics

That's a good guide. Nice find. Add that to the existing Raspbian config (which is quite good at setting up the default zones which even a forwarder should serve rather than recurse). Not sure why they are forcing IPv4 only. It works fine on my IPv4+IPv6 home network. Anyways, the answer is in two p...

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