Technical stuff about Perl, Linux and computing & technology in general.
A note for my own reference, as I always forget how to create a remote branch then work with it later:
Create a new remote branch topic/add_awesomeness with, e.g.:
git push origin :origin:refs/heads/topic/add_awesomeness
Create a new local branch to track it:
git checkout --track -b add_awesomeness origin/topic/add_awesomeness
The unintuitive way to delete a remote branch is:
git push origin :heads/topic/doc_cleanup
(There must be a better way than that…)
My current backup solution is using rdiff-backup to do incremental backups. I’d previously been using plain rsync, but I wanted snapshots too, so I could retrieve a file as it looked at some point in the past (as Sod’s law guarantees that if a file was mistakenly deleted/clobbered, rsync will run between that happening and you noticing, so the backup will be clobbered too).
My setup involves the backup box running rdiff-backup, connecting to the machine to be backed up via SSH, using a passwordless SSH key for authentication. The entry in ~/.ssh/authorized_keys on the machine to be backed up allows that key to be used only to run rdiff-backup, nothing else, and only from the backup host, to provide as much security as possible.
I thought I’d document my setup here, both for easy future reference for myself when adding other boxes to back up, and for anyone else who may find it useful.
So, the steps I use are as follows:
Continue reading Incremental backups with rdiff-backup
On 11th March 2011, CPAN testers reached the milestone of 11 million CPAN testers reports.
That’s an awful lot of code testing! CPAN Testers are damned useful, automatically testing CPAN modules on various platforms to make sure all is as it should be – a very valuable part of the CPAN ecosystem.
I wrote a basic Nagios plugin named nagios_3ware_raid_check to monitor the status of RAID arrays on 3ware/LSI hardware RAID controllers, but it was pretty limited.
Today I got a chance to improve it as I needed it for some machines at work; it now automatically figures out which card(s) are present, and checks the status of each RAID array on it. This means you don’t need to configure it to know which card number and unit to monitor, it just Does The Right Thing.
It uses the tw_cli utility available from the LSI website, which supports a wide range of 3ware/LSI RAID cards.
Example:
[dave@rasputin:~]$ /usr/local/bin/nagios_3ware_raid_check -v Card 6 is a 8006-2LP Unit u0 on card6 is a RAID-1 array of 931 GB and is OK RAIDCHECK OK - Card 6 unit u0 RAID-1 OK (931GB)
When actually using it from Nagios, don’t use the -v (verbose) option – just use something like the following in nrpe_local.cfg:
# Monitor RAID status command[check_raid]=/usr/local/bin/nagios_3ware_raid_check
For security, I like to run CPAN.pm as a normal user so building & testing modules are all performed as a user rather than root, but of course the final installation needs to be done as root so that files can be copied to paths not writeable by normal users.
I always forget the options I need, so for my future reference as well as anyone else who finds it useful:
o conf make_install_make_command 'sudo make' o conf mbuild_install_build_command 'sudo ./Build'
That means that the actual installation gets run via sudo, with everything else just being done as the user you started the CPAN client as.
(Of course, these days, you could also use cpanm (cpanminus) with its –sudo option…)
A particular box at $work had been slow to SSH to for a while, and I finally wanted to spend the time to find out why.
Running ssh -v thatmachine showed that it was hanging whilst attempting to authenticate with GSSAPI, with the slow section looking like:
debug1: SSH2_MSG_SERVICE_REQUEST sent debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,gssapi-with-mic,password debug1: Next authentication method: gssapi-with-mic debug1: Unspecified GSS failure. Minor code may provide more information Credentials cache file '/tmp/krb5cc_1000' not found debug1: Unspecified GSS failure. Minor code may provide more information Credentials cache file '/tmp/krb5cc_1000' not found debug1: Unspecified GSS failure. Minor code may provide more information debug1: Next authentication method: publickey debug1: Offering public key: /home/davidp/.ssh/id_rsa # authentication by public key then proceeded quickly
SSHing to the machine by IP instead, i.e. ssh -v 10.1.1.192, produced slightly different output:
debug1: Authentications that can continue: publickey,gssapi-with-mic,password debug1: Next authentication method: gssapi-with-mic debug1: An invalid name was supplied Cannot determine realm for numeric host address debug1: An invalid name was supplied Cannot determine realm for numeric host address debug1: An invalid name was supplied debug1: Next authentication method: publickey # authentication by public key then succeeded quickly
It’s clear that it’s trying to authenticate using GSS-API (Kerberos), failing, then moving on to public key auth.
The fix is simple – disable attempts to use GSS-API by adding the following to ~/.ssh/config:
GSSAPIAuthentication no
Before adding that:
[davidp@columbia:~]$ time ssh 10.1.1.192 touch /dev/null | grep real real 0m15.512s
After adding it:
[davidp@columbia:~]$ time ssh 10.1.1.192 touch /dev/null | grep real real 0m0.611s
Problem solved.
The wireless kill-switch (Fn+F2) on my Dell Inspiron 17R (N7010) laptop is getting on my tits, as I occasionally hi that key combination by accident when trying to use Ctrl + F2.
I can’t seem to see any way to disable this, and Google doesn’t seem to be able to find anything useful. Anyone have any ideas? There must be some way to ignore that key combination.
Running xev whilst pressing that key combination shows me:
KeyPress event, serial 33, synthetic NO, window 0x5c00001,
root 0xb0, subw 0x0, time 39357273, (121,-345), root:(1426,350),
state 0x0, keycode 246 (keysym 0x1008ff95, XF86WLAN), same_screen YES,
XLookupString gives 0 bytes:
XmbLookupString gives 0 bytes:
XFilterEvent returns: False
KeyRelease event, serial 33, synthetic NO, window 0x5c00001,
root 0xb0, subw 0x0, time 39357273, (121,-345), root:(1426,350),
state 0x0, keycode 246 (keysym 0x1008ff95, XF86WLAN), same_screen YES,
XLookupString gives 0 bytes:
XFilterEvent returns: False
So, if it’s being triggered by software, it’s keycode 246 I need to deactivate/map to something else, I believe.
However, I tried with:
xmodmap -e 'keycode 246 = NoSymbol'
… but no effect, it still kills the wireless. I’m hoping that someone might know how to do it, and/or that someone else Googling for how to do this will find this post, and perhaps share any ideas. If I figure it out, I’ll of course update this post with the solution.
UPDATE – I probably should have mentioned that this machine is running Ubuntu Linux. Also, I found that, in System > Preferences > Keyboard Shortcuts, I can assign a shortcut to the Fn+F2 key combination (the shortcut column shows 0xf6), and pressing Fn+F2 does indeed trigger that shortcut (launching a terminal window, for a test), but also still triggers the wifi killswitch. I suspect that, as well as being seen by the OS and software, it’s being directly intercepted by hardware to toggle the card?
UPDATE – to help people Googling for info on how to disable the wireless/wifi kill switch key combination / shortcut for this laptop, it’s a Dell 17R / N7010 with a Broadcom BCM4313 802.11b/g LP-PHY wireless adaptor.
Just for fast and easy reference really, but for easy debugging to find out the exact HTTP requests being sent and HTTP responses received by a web-scraping script using the excellent WWW::Mechanize, you can simply add:
$mech->add_handler("request_send", sub { shift->dump; return });
$mech->add_handler("response_done", sub { shift->dump; return });
This will cause all HTTP requests and responses to be output, so you can see exactly what’s happening.
Just a quick post about jnettop, a tool I find really useful for monitoring network traffic to see what other machines a machine is talking to, and how much traffic is being sent/received between them. (It also includes traffic going via the host you’re running it on, so very useful for firewall/gateway machines.)
Jnettop is a traffic visualiser, which captures traffic going through the host it is running from and displays streams sorted by bandwidth they use.
Basic screenshot:
Useful stuff.
This afternoon, ATV Johannes Kepler docked with the International Space Station (video here).
It’s delivering “4,534kg of propellant for International Space Station reboost and attitude control”, “1,600kg of dry cargo, 850kg of propellant for Russia’s Zvezda module and 100kg of oxygen”. Whilst attached to the ISS, it will “boost” it, compensating for decaying orbit caused by drag.
The thing, once released from the launch rocket, navigates itself into orbit behind the ISS, and automatically docks with it with astonishing 1.5 cm precision, all whilst while the spacecraft and the ISS are hurtling around the Earth at 28 000 km/h. Impressive stuff indeed. (See ATV flight phases.)