What is the syntax of `/etc/initramfs-tools/conf.d/*` files?

Unix Debian
, ,
2

File /etc/initramfs-tools/conf.d/mdadm (as well as other files in the /etc/initramfs-tools/conf.d/ directory) is essentially a configuration file in the format «environment variables = values», which is processed by initramfs-tools scripts when creating the initramfs.

Main points of the syntax

  1. Each line usually contains either:

    • A variable assignment (for example, BOOT_DEGRADED=true),
    • Or a comment,
    • Or an empty line (which the scripts ignore).

  2. Variable assignments are done in the style of simple shell variables:

    VARIABLE="value"
VARIABLE2=yes

    Double or single quotes are not mandatory if the value does not contain spaces or special characters, however, for reliability, quotes are used more often.

  3. Comments are designated with the # symbol. Everything that follows # in a line is ignored. For example:

    # This is a comment
BOOT_DEGRADED=true   # This is also a comment (at the end of the line)

  4. Empty lines can be inserted for readability, they are ignored.

Example contents of /etc/initramfs-tools/conf.d/mdadm

# Allow booting with a "degraded" RAID array
BOOT_DEGRADED=true

# Specify that the mdadm config is in the standard location
MDADM_CONF=/etc/mdadm/mdadm.conf

At the same time, the set of available variables for the mdadm file can differ in different distributions or versions of initramfs-tools. The most commonly encountered ones are:

  • BOOT_DEGRADED=true|false
    Indicates whether the boot process is allowed if the RAID array is not in a complete state.

  • MDADM_CONF=/path/to/mdadm.conf
    If there is a need to specify an alternative mdadm configuration file.

  • (In some systems) DEVICE=... or ARRAY=...
    But such settings are more often specified directly in /etc/mdadm/mdadm.conf, rather than in conf.d/mdadm.

How to write comments

In order to comment out a line, it is sufficient to place # at the beginning of the line or before the text that needs to be turned into a comment. Example:

# This is a completely commented-out line
BOOT_DEGRADED=true   # This is a setting with a comment at the end

Thus:

  1. At the beginning of the line: # Comment.
  2. After a command or variable: VARIABLE=value # explanation.

Everything that follows the # symbol in any line is ignored when read by the initramfs-tools scripts.