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Connman: How to enable Debug Messaging

To enable message logging in connman the code needs to be called with the argument -d. If you are building the code under yocto you can either modify the connman.service.in file in the src directory to include the following lines. This will cause the appropriate changes to be written to the rootfs everytime it’s built.

EnvironmentFile=/home/root/connman.env
ExecStart=@sbindir@/connmand -n $DEBUG

Alternatively the changes could be made directly to the systemd configuration file connman.service.

The lines above make use of an environment variable $DEBUG which is being set in the file /home/root/connman.env, which contains the following lines.

DEBUG=-d
CONNMAN_SUPPLICANT_DEBUG=1

The -d argument is used to turn on debugging. By adding additional parameters to this line it is also possible to specify which files we want to get debug messages from.

The CONNMAN_SUPPLICANT_DEBUG variable is included because some messaging in connman is enabled according to environment variable settings. The wifi.c file for example includes the following function.

static void debug(const char *str)
{
  if (getenv("CONNMAN_SUPPLICANT_DEBUG"))
    connman_debug("%s", str);
}
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Out of RAM: Increase a meagre swapfile under Linux

Swap space is an area set aside for use in the event that physical RAM becomes full. On a Linux machine, when the system runs out of RAM inactive pages are moved to the Swap Space freeing up RAM.

Whilst building a Yocto Image on an old machine with limited RAM I was getting repeated failures during the compilation of qtbase. Analysis of the kernel log revealed that there was a shortage of memory, and hence a need to increase the swap space.

You can determine the current status of the swap space using the following command

$ sudo swapon --show
NAME      TYPE SIZE   USED PRIO
/swapfile file   2G 265.9M   -2

To increase the size of the swapfile, begin by disabling the swap space, and then remove the existing swapfile.

sudo swapoff /swapfile
sudo rm /swapfile

You can now create a new blank swapfile, set the permissions associated with it, and then re-enable the swap space.

sudo dd if=/dev/zero of=/swapfile bs=1M count=8192
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

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Yocto: How to assign variables with examples

  • = A hard assignment. The variable is assigned as soon as the statement is evaluated. If the assignment contains a reference to another variable then that reference will be included in the assignment rather that the value of the reference.
  • ?= Defines a variable only if it is undefined at the time of parsing.
  • ??= Assignment does not occur until the end of the parsing process.
  • := Immediate variable expansion
  • += Appending with spaces.
  • =+ Prepending with spaces.
  • .= Appending without spaces.
  • =. Prepending without spaces.

Assignment Using Overrides

Variables can be appended or prepended using the override style syntax. In the example below B becomes equal to “bval additional data” and C becomes equal to “additional data cval”. Note that no additional spaces are include over what is in the original variable definitions.

B = "bval"
B_append = " additional data"
C = "cval"
C_prepend = "additional data "

Removal of data can also be accomplished. In the following example FOO becomes equal to “ghi abcdef”. Note that surrounding spaces are also removed.

FOO = "abc def ghi abcdef abc def abc def"
FOO_remove = "abc def"

Examples

In the following example the value of A is set to “aval”. The value of B is set to “pre${A}post”. In other words the value of B becomes dependent on the value of A at the times it is referenced. If the value of A changes between references to B the value of B will be different at those times.

A = "aval"
B = "pre${A}post"

The following code includes some immediate variable assignment. The value of A becomes “test 123” as the values of A and B are unassigned at the time of As assignment.

T = "123"
A := "${B} ${A} test ${T}"

The following code uses a soft assignment. A is only assigned if the value is currently unassigned. The code therefore results in A being given the value of “one”

A ?= "one"
A ?= "two"

The following code uses weak assignment. A is not assigned until the end of the parsing process and is therefore given a value of “two”

A ??= "one"
A ??= "two"

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Yocto: base_contains

The base_contains function is used to return a value based on a search of a named variable for a given value. The following line of code for example would search the DISTRO_FEATURES variable for the text bluetooth and if found it would return the text bluez5 otherwise we would get a blank.

"${@base_contains('DISTRO_FEATURES', 'bluetooth', 'bluez5', '', d)}"
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Yocto: Setting the root password

To set the root password under a Yocto build you need to add the following code to the local.conf file located in the build/conf directory.

INHERIT += "extrausers"
EXTRA_USERS_PARAMS = "usermod -p Rbna8drt0yYLk root;"

Where the Rbna8drt0yYLk value is generated via the command

$ openssl passwd <password>