Jun 292019
 

(And apologies for the misspelling; that words is spelt “civilisation” around these parts)

So I’m a Linux user and whilst I don’t often play games, an occasional break spending time slaughtering pedestrians (in GTA V) or conquering the world (in ‘Civilization’) can be fun.

Except that I have not been able to play Civilization V since I bought it through Steam – usually instant crashes although sometimes it worked well enough for a few turns.

Today I sat down and tried out various suggestions on fixing it until I found one that worked for me :-

  1. Right-click the game name in Steam.
  2. Select “Properties”
  3. Select “Startup options”
  4. Specify one of the following :-
    1. (Failed for me) LD_PRELOAD=’./libcxxrt.so:/usr/$LIB/libstdc++.so.6′ %command%
    2. (Failed for me) LD_PRELOAD=/usr/lib32/libopenal.so.1 %command%
    3. taskset –cpu-list 0-3 %command%

As implied, the “taskset” startup option appears to have worked for me. According to the site I nicked it from, Civilization has trouble running on systems with more than 8 core threads.

Tower Stonework
Jun 082019
 

Quite a while ago, I “borrowed” some inscrutable zsh magic to automatically add the contents of ~/.ssh/known_hosts to a known_hostsi variable and used that variable to perform host name completion for certain commands. Once ssh started hashing the known_hosts file, this broke and I was busy at the time and stopped using it.

Ages later, I’ve fixed it and enhanced it a bit (and arguably made it a bit simpler). Not only does it pick up host names from the known_hosts file but also adds a list from lxc-ls and adds a few static host names (with one exception, not shown). This is done by adding the following to .zshrc :-

knownhosts=( $(sudo -b lxc-ls) )
#       Pick up a list of hosts from lxc-ls
knownhosts+="localhost"
#       Add static hostnames
for x in $(grep -v "|" ~/.ssh/known_hosts | awk '{print $1}' | awk -F, '{printf "%s ", $1}')
do
  knownhosts+=$x
done
#       Pull a list of hosts out of ~/.ssh/known_hosts excluding the Hashed hosts.
zstyle ':completion:*:(ssh|scp|sftp|ping|nmap):*' hosts $knownhosts
#       Commands to use a list of known hosts with

That probably is not the most efficient code, but does have the advantage that it is relatively easy to follow.

One addition is to add the option HashKnownHosts no to ~/.ssh/config.

There is of course a risk associated with disabling the hashing of host names within the known_hosts file. If your host becomes compromised, malicious code can use that file to obtain a list of hosts with which there is a trust relationship making it easier for an attacker to pivot through your network.

Jun 052019
 

On previous occasions (yes that does mean more than once) I have messed around with the network configuration of containers to get :-

  1. A consistent behaviour.
  2. A fixed IPv4 address with no DHCP configuration (this one is easy).
  3. A fixed IPv6 address with no autoconfigured global addresses (this one has been tricky)

This turns out to be relatively easy providing that you configure the addresses within the container rather than within the container configuration. At least it looks good to go so far (I’ve been mistaken in the past).

The container configuration is quite simple :-

lxc.net.0.type = veth
lxc.net.0.flags = down
lxc.net.0.link = br0

Note that the bridge interface (br0) may be different. Also note that there is no lxc.net.0.ipv4.address, lxc.net.0.ipv4.gateway, lxc.net.0.ipv6.address, or lxc.net.0.ipv6.gateway.

The configuration within the container is dependent on what userland you are running, but for Debian (and Ubuntu if you’re not using Netplan) :-

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
    address 10.0.0.34/16
    gateway 10.0.0.1

iface eth0 inet6 static
    address 2001:0db8:cafe:dead:0000:0000:0000:3eb/64
    scope global
    gateway 2001:0db8:cafe:dead:0000:0000:0000:0001
    privext 0
    accept_ra 0
    autoconf 0

Not sure quite which options are required but having all of “privext 0”, “accept_ra 0” and “autoconf 0” does mean no additional autoconfigured IPv6 addresses.

(And no the part number of this post isn’t anything more than a joke)

Apr 102019
 

So earlier today, I had a need to mount a disk image from a virtual machine on the host, and discovered a “new” method before remembering I’d made notes on this in the past. So I’m recording the details in the probably vain hope that I’ll remember this post in the future.

The first thing to do is to add an option to include partition support in the relevant kernel module, which I’ve done by adding a line to /etc/modprobe.d/etc-modules-parameters.conf :-

options nbd max_part=63

The next step is to load the module:

# modprobe nbd

The next is to use a Qemu tool to connect a disk image to a network block device :-

# qemu-nbd -r -c /dev/nbd0 /home/mike/lib/virtual-machine-disks/W10.vdi
# ls /dev/nbd0*
/dev/nbd0  /dev/nbd0p1  /dev/nbd0p2  /dev/nbd0p3

And next mount the relevant partition :-

# mount -o ro /dev/nbd0p2 /mnt

All done! Except for un-mounting it and finally disconnecting the network block device :-

# umount /mnt
# ls /dev/nbd0*
/dev/nbd0  /dev/nbd0p1  /dev/nbd0p2  /dev/nbd0p3
# qemu-nbd -d /dev/nbd0
/dev/nbd0 disconnected
# ls /dev/nbd0*        
/dev/nbd0

The trickiest part is the qemu-nbd command (so not very tricky at all).

The “-r” option specifies that the disk image should be connected read-only, which seems to be sensible when you’re working with a disk image that “belongs” to another machine. Obviously if you need to write to the disk image then you should drop the “-r” (but consider cloning or taking a snapshot).

The “-c” option connects the disk image to a specific device and the “-d” option disconnects the specific device.

Old Metal 2
Feb 092019
 

One of the things that irritates me about fancy new service management systems like systemd is that unless you get everything exactly right, you can end up with things interfering with specific configuration files – specifically /etc/resolv.conf.

Now as a DNS administrator, I have a certain fondness for manually controlling /etc/resolv.conf and it does actually come in useful for making temporary changes to test specific DNS servers and the like. The trouble comes when something else wants to control that file.

The ideal fix for this conflict is to have things like systemd control a separate file such as /etc/system/resolv.conf.systemd, and for /etc/resolv.conf be installed as a symbolic link pointing at the real file.

But back in the real world, if you do disable systemd-resolver which can be done with: systemctl disable systemd-resolved.service; systemctl stop systemd-resolved.service

Then you may also want to make the file immutable: chattr +i /etc/resolv.conf. On at least one server, systemd merrily re-created /etc/resolv.conf as a symbolic link to an empty file despite systemd-resolved being disabled.

Corner Of The Pyramid
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