Aug 202013
 

Every so often I come across an old Linux box that doesn’t take kindly to being rebooted. Without console access, it is hard to see what is going on, but the Linux kernel gets stuck trying to mount the root file system. There are many possible fixes for this, but they all have one thing in common … a work-around has to be performed to get the box up and running.

The console gets stuck in a “mini-root” environment loaded when the initrd image is loaded and before the real root file system is mounted which means a lot of commands are not available, but lvm should be available. First of all, run lvm lvscan to get a list of the logical volumes that need activating :-

(initramfs) lvm lvscan
  inactive          '/dev/sys/root' [332.00 MiB] inherit
  inactive          '/dev/sys/usr' [8.38 GiB] inherit
  inactive          '/dev/sys/var' [2.79 GiB] inherit
  inactive          '/dev/sys/swap_1' [7.05 GiB] inherit
  inactive          '/dev/sys/tmp' [380.00 MiB] inherit
  inactive          '/dev/sys/home' [16.00 GiB] inherit
  inactive          '/dev/sys/opt' [24.00 GiB] inherit

For each volume group (the second column, middle word), run: lvm lvchange -ay ${volume-group-name}. In the case of my example :-

(initramfs) lvm vgchange -ay /dev/sys
  7 logical volume(s) in volume group "sys" now active

At which point you should be able to press ^D (or enter exit) to continue the boot process.

A slighter better work-around involves changing the Grub configuration to add a delay to the kernel parameters. This sections assumes that you are not using Grub Legacy!

Start by editing /etc/default/grub and changing the variable GRUB_CMDLINE_LINUX to include “rootdelay=20” :-

GRUB_CMDLINE_LINUX='console=tty0 console=ttyS0,19200n8 rootdelay=20'

Finalise by running update-grub. This adds a 20s delay to the boot process so is hardly an ideal solution.

Feb 222013
 

The Raspberry PI is a pretty cool device, but it is not the only small cheap computer around, and given that the PI is more hardware hacking orientated I thought I’d dig up some links for some of those other devices. Especially as I’ve got two Arduino projects on the go.

There’s actually a surprising number of devices out there; some running Linux and some running Android. And in a surprising variety of form factors; I’ve avoided looking at the simple boards – the point here is to look at devices that are different :-

  1. The Trim-Slice looks quite an interesting device, but all seems to have gone quiet since March 2012.
  2. The Giada Q11 is a similar device which is about the size of a VCR … or a 3.5″ external hard disk enclosure.
  3. The Cloud Client mini PC is a touch smaller being roughly the size of a double-CD case.
  4. The CuBox is more square than the rest and is roughly the same size as a mains plug.
  5. The Cotton Candy is an ARM in a USB stick; a cheaper option but possibly via Ebay is the U2, although most cheaper options don’t have quite the same features as the Cotton Candy.

This is not to imply that there are not others out there, nor that these are “better” in any way. I’ve not used any of them.

Feb 062013
 

If you have previously used Linux’s volume manager (LVM) to set up disk storage, you may want to know about how to grow a filesystem safely.

Which is probably the big feature of any decent volume manager because accurately predicting the size of filesystems is a black art, and the only alternative – to make the root filesystem contain all of the storage is a dumb idea.

It’s actually really easy and can be done non-disruptively. It is done in two parts – effectively growing the “disk” device and then growing the filesystem itself.

Extending The Volume

First identify the volume you need to extend. You can of course simply run lvscan which will show a list of the volumes, and if you have named them sensibly will allow you to pick out the volume to extend. But the simplest way is simply to run df to look at the filesystem you want to extend :-

/dev/mapper/ssd-opt         7.9G  5.5G  2.1G  73% /opt

The device (in the first column) is what we extend. Now to decide how much to grow the volume by; just for the case of this example, we’ll assume that 2Gbytes is a sensible amount to grow the volume by. The command needed is :-

lvextend --size +2G /dev/mapper/ssd-opt

And that’s it. No need to shut down the server, dismount the filesystem, etc. Of course we haven’t quite finished yet.

Growing The Filesystem

What we have done at this point is the equivalent of making the disk bigger. We also need to tell the filesystem it is sitting on a bigger disk, and to do so we need to know the type of the filesystem. The canonical place for checking that is the file /etc/fstab (actually it’s the filesystem itself but that is going too far) :-

# grep opt /etc/fstab
/dev/mapper/ssd-opt	/opt		ext4	noatime		0 3

It is probable that you are looking at growing an ext3, ext4, or xfs filesystem. If not you will have to look up the details yourself.

Growing ext3, or ext4 Filesystems

This is done with the resize2fs command :-

resize2fs /dev/mapper/ssd-opt

Several points :-

  1. Yes it can be done “online” whilst the filesystem is mounted (and applications are busy using it).
  2. You need to specify the device containing the filesystem to grow and not the mount point.
  3. There is no need to specify the size … the size will be determined from the size of the device underneath the filesystem.

Growing xfs Filesystems

This is done with the xfs_growfs command :-

# xfs_growfs /opt

Several points :-

  1. Yes, it can be done “online”. In fact you have to do it with the filesystem mounted.
  2. You need to specify the mountpoint of the filesystem and not the device. Irritatingly different from the above!
  3. There is no need to specify the size.

How Reliable Is This?

Very.

There is always the chance that something could go wrong especially if you are operating “at the edge” (say you have a filesystem that is unusually large – several petabytes). But I’ve done online filesystem resizing for years in countless circumstances without an issue.

I’ll quite happily do it on the most important systems during working hours without losing a moment’s thought. However I do work in a place that takes backups seriously!

Jan 112013
 

Customising keyboard maps in Linux is somewhat … confused with lots of different tools and layers to perform the same task. There are a number of tools for performing some form of keyboard mapping, but the most common ones have some disadvantages :-

  •  xkb (which is the modern X way), and xmodmap (which is deprecated but conveniently has a very simple syntax for dealing with a single key) both work fine for ordinary keys but cannot do anything with “unusual” keys not passed into X. Just look online for just how many people have trouble with multimedia keys not being recognised.
  • The PS/2-specific tools of dumpkeys, loadkeys, and setkeycodes which work fine, but are somewhat reluctant to help out with USB keyboards.
  • Plus the desktop environment you are using may well have its own idea of how the keyboard will be used (GNOME has a nasty tendency to grab the menu key away from me).

There is fortunately another way which is rather difficult to find information about. Which is the reason behind this posting of course.

This “other method” is to use the generic input system to perform the keyboard mapping which has certain advantages over other methods. Most of the information to do this came from a README file contained within the source code.

The Example Keyboard

To demonstrate keyboard mapping, it is helpful to have an example keyboard with custom mappings to play with. Many of the keyboards I use this for are rather complex with many mappings, but I also have a mini keyboard with relatively few mappings :-

Original Key new function
Esc Lock screen
`/~ Esc
Caps Lock Control
Insert Delete
Delete `/~

No great mystery as to why I want my keyboard mapped this way – I’m just fussy about keyboards.

The Basic “Tool”

In fact there is just one tool – /lib/udev/keymap – which performs all of the relevant tasks. Before it can do anything, it needs to be provided with the path of the relevant input device. This is easiest done from the console (rather than in X) as root. The easiest way of identifying the device is to unplug the keyboard, reboot the machine, and :-

# ls /dev/input/e* > /var/tmp/old.list
[Plug in keyboard]
# ls /dev/input/e* > /var/tmp/new.list
# diff /var/tmp/old.list /var/tmp/old.list
> /dev/input/event13
> /dev/input/event14

If you are lucky, there will be just one new input device. If not, you will have to try each one in turn. The first job is to record the keycode of each key to be customised in turn. To do this, it is necessary to run keymap with the input device and the “-i” option, and each keystroke will result in some output :-

# /lib/udev/keymap /dev/input/event13 -i
Press ESC to finish, or Control-C if this device is not your primary keyboard
scan code: 0x70029   key code: esc
# /lib/udev/keymap /dev/input/event13 -i
Press ESC to finish, or Control-C if this device is not your primary keyboard
scan code: 0x70035   key code: grave
scan code: 0x70039   key code: capslock
scan code: 0x70049   key code: insert
scan code: 0x7004C   key code: delete

A key can be mapped temporarily using keymap. But before that a list of possible key names is useful to have; there is one to be found in /usr/include/ :-

# grep KEY_ /usr/include/linux/input.h | less

The relevant name would be the part that follows the “KEY_” converted to lower-case.

# /lib/udev/keymap /dev/input/event13 0x70035 esc

But that is rather a temporary solution; it is better by far to create a file containing the necessary mappings to be automatically applied :-

# cat /tmp/custom-filco.map
0x70029 screenlock
#	Original: key code: esc
0x70035 esc
#	Original: key code: grave
0x70039 leftctrl
#	Original: key code: capslock
0x70049 delete
#	Original: key code: insert
0x7004C insert
#	Original: key code: delete

Making The Mappings Permanent

The first step is to obtain some details to uniquely (or as much as possible) identify the keyboard. Run :-

# udevadm info --export-db > /tmp/udev-db.txt

And look through the output for the input device you previously used. Look for a ID_VENDOR_ID and ID_MODEL_ID that you can use.

Next add a rule to /lib/udev/rules.d/95-keymap.rules along the lines of :-

ENV{ID_VENDOR_ID}=="04d9", ENV{ID_MODEL_ID}=="2011", RUN+="keymap $name custom-filco.map"

Once this is working you may want to add it to your version of custom-filco.map as a comment to preserve it for use after upgrades; alternatively you may wish to create a new file that will not get overwritten.

Before activating the new rule, remember to copy /tmp/custom-filco.map into /lib/keymaps/custom-filco.map. And again keep another copy in a safe place to preserve.

As to how to activate, a reboot is probably the simplest way.

Dec 312012
 

This has been updated for Awesome 3.5

I have long been interested in tiling window managers, which would seem to offer the flexibility I crave. But switching is painful when you want your machine to be as functional as much as possible. On at least two occasions I have switched … and very quickly switched back when problems were encountered.

So just for the fun of it, I have decided to give it another go … in a way that can be gradually worked into functionality.

But first, what exactly is a tiling window manager? Well a conventional window manager works with overlapping windows where windows can stack on top of each other and overlap. A tiling window manager on the other hand uses tiling to maximise the size of every displayed window.

Or in other words, if you want to make the maximum use of space on your screen, a stacking window manager usually asks you to manually move and resize windows yourself whereas a tiling window manager does it all automatically. Although with a tiling window manager, you will need to rotate amongst different tiling layouts to suit.

Tiling window managers tend to be keyboard driven rather than mouse driven, but this is merely an aspect of their implementation.

A Testing Environment

The key to setting up any window manager gradually over time without losing an existing working environment, is to create a separate display which a new window manager can control. This can be quite easily accomplished with a nesting X server, which is provided by the xserver-xephyr package.

As to the choice of window manager, the title of this post gives away the secret – Awesome. Of course the same method works for other window managers too.

The first step is to install the required packages :-

sudo apt-get install xserver-xephyr awesome awesome-extra

The next step is to create a simple shell script to start the nested X server. This basically starts the nested X server with a sensible screen size, and sets the $DISPLAY environment variable so that any further X programs are directed to communicate with the nested X server. The nested X server simply starts up as a standard window within which Awesome operates. The script looks like :-

#!/bin/sh

Xephyr -ac -reset -screen 1280x1000 :1 &
export DISPLAY=:1.0
sleep 5
awesome --config ~/src/site/etc/awesome/config.lua

The sleep command in there is to wait until X has settled down before trying to manage it … without this, it is possible that awesome will fail to open the display (on a slower laptop it worked without; on a faster desktop it did not). The parameter to awesome is to set the preferred location for the configuration file (which I will describe next), although you can leave it out to use the default.

Don’t start it yet! Before doing that, copy the default configuration file to the specified location so you have something to work with :-

cp /etc/xdg/awesome/rc.lua ~/src/site/etc/awesome/config.lua

It’s All In The Repository

The custom configuration file I specified just happens to point to a directory and file within the working copy of a Subversion repository. Using a repository for configuration files has all sorts of benefits; not least of which is to reverse “poor” choices made along the way. Whilst describing how to get one set up is beyond the purpose of this post, it is well worth doing.

Of course if you are working with a repository, it is important to remember to commit changes at every stage :-

% svn add ~/src/site/etc/awesome 
A         /home/mike/src/site/etc/awesome
A         /home/mike/src/site/etc/awesome/config.lua
% svn commit ~/src/site/etc/awesome -m "Awesome: Initial Configuration from default"
Adding         src/site/etc/awesome
Adding         src/site/etc/awesome/config.lua
Transmitting file data .
Committed revision 166.

I won’t be documenting every single commit, but they are all in there!

It is also helpful (at this stage) to create a symlink between the default configuration directory (~/.config/awesome) and the working copy of your repository. The configuration directory can probably be changed, but one thing at a time!

Status Bar Size

One of the annoyances I remember from the last time I played with Awesome, was the tiny size of the status bar. It is all very well maximising the size of the main screen area, but some of us have high resolution screens and tired old eyes! Within the config.lua file (or whatever you named your file), look for :-

mywibox[s] = awful.wibox({ position = "top", screen = s})

And change it to add a height parameter :-

mywibox[s] = awful.wibox({ position = "top", screen = s, height=32 })

The exact choice of size is of course down to personal preferences! However changing the size also means changing the font would be wise :-

awesome.font = "LMSans10 10"

Making the font too much larger will result in some display oddities … at least for now.

Adding A Title Bar

In theory, there is no need for a title bar with a tiling window manager, but I guess I am a little too conventional as a window without a title bar still looks a little weird to me. Plus my shell prompts stick useful bits of information into the window title bar and I would really rather hang on to that extra information. Still, drawing title bars on windows turns out to be really simple … just find the existing code to do so and :-

local titlebars_enabled = true

Some appearance tweaks and indeed messing around with the unnecessarily large number of buttons could be usefully accomplished, but for now this is fine.

 

Themes

Of course messing around with the appearance of a window manager is probably best dealt with using themes (if they are supported). The default configuration file I worked with included enabling beautiful via :-

require("beautiful")
beautiful.init("/usr/share/awesome/themes/default/theme.lua")

It is easier to tinker with themes with a configuration file you can edit, so I copied this theme.lua to the configuration directory named as default-theme.lua, and changed the configuration :-

-- beautiful.init("/usr/share/awesome/themes/default/theme.lua")
beautiful.init(awful.util.getdir("config") .. "/default-theme.lua")

I also removed the previous section’s font setting and set the same font within the new configuration file :-

theme.font = "LMSans10 10"

To cope with the larger font, I also increased the width of each menu item :-

theme.menu_width  = "300"

Although this width does depend on having an appropriately sized screen, and not having too many levels to your menu (if it gets too wide, the extra levels don’t appear neatly).

And finally I commented out the command used to set the background … having a background image for a tiling window manager (which is designed to utilise the whole screen) is a touch unnecessary. And I don’t particularly like the default image :-

--theme.wallpaper_cmd = ...

For now I will leave the colours alone … the defaults may not be perfect but are not sufficiently irritating to spend time on right now. But the details of how to change colours of various components can be found in the theme file we have created.

Disabling Layouts

Personally I believe that you can have too much of a good thing, and choosing between the rather large number of different possible layouts that Awesome makes available is one of those. To reduce the number of possibilities, simply comment out some of the possibilities when setting the “layouts” variable in the configuration file :-

layouts =
{
    awful.layout.suit.floating,
    awful.layout.suit.tile,
    --awful.layout.suit.tile.left,
    --awful.layout.suit.tile.bottom,
    --awful.layout.suit.tile.top,
    awful.layout.suit.fair,
    --awful.layout.suit.fair.horizontal,
    awful.layout.suit.spiral,
    --awful.layout.suit.spiral.dwindle,
    awful.layout.suit.max,
    --awful.layout.suit.max.fullscreen,
    --awful.layout.suit.magnifier
}

Which you command out does not matter so much, and indeed you may very well change you mind at a later point.

A Menu

Whilst the menu built into Awesome has undoubtedly many advantages, I already have a somewhat adequate menu built up over years that relies on myGtkMenu. Whilst changing this menu could well be sensible, it does also seem sensible to keep it around during the transitional period. To do so is simply a matter of replacing certain bindings :-

 -- {{{ Mouse bindings
 root.buttons(awful.util.table.join(
-    awful.button({ }, 3, function () mymainmenu:toggle() end),
+    --awful.button({ }, 3, function () mymainmenu:toggle() end),
+    awful.button({ }, 3, function () awful.util.spawn("/opt/bin/myGtkMenu /home/mike/lib/root.menu") end),
     awful.button({ }, 4, awful.tag.viewnext),
     awful.button({ }, 5, awful.tag.viewprev)
 ))

If you hadn’t guessed, I’ve started using diffs to show the changes where it makes sense; if you cannot read diffs, this page is probably not for you.

That bit replaces the root window, but not the status bar menu :-

 mylauncher = awful.widget.launcher({ image = image(beautiful.awesome_icon),
-                                     menu = mymainmenu })
+--                                     menu = mymainmenu })
+                                       command = "/opt/bin/myGtkMenu /home/mike/lib/root.menu" })

My own menu has some issues in that it doesn’t yet have anything to control awesome itself. But is good enough to get started with.

Final Word … Or Not!

And that is it! Or at least it is enough to be getting on with.