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Revision as of 13:51, 22 November 2013 by Graysky (Talk | contribs) (Benefits of modprobed-db with make localmodconfig in custom kernels)

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Summary help replacing me
Describes the installation and usage of modprobe db.

modprobed-dbAUR keeps a running list of ALL modules ever probed on a system and allow for easy recall. This is very useful for users wishing to build a minimal kernel via a make localmodconfig which simply takes every module currently probed and switches everything BUT them off in the .config for a kernel resulting in smaller kernel packages and reduced compilation times.

Installation and Setup

  1. Download, build, and install modprobed-dbAUR.
  2. Run /usr/bin/modprobed-db which will create $XDG_CONFIG_HOME/modprobed-db.conf if one does not already exist. Optionally add some modules to ignore to the IGNORE array. Some common ones are included by default.


Data Collection

The most convenient method to use modprobed-db is to simply add a crontab entry invoking /usr/bin/modprobed-db store at some regular interval.

Example running the script once every 20 minutes:

$ crontab -e
*/20 * * * *   /usr/bin/modprobed-db store &> /dev/null

Another way is to use systemd's built-in timer functionality. Refer to systemd/cron functionality#Custom/Example service files to do the same.

Data Recall

As mentioned earlier, this script is meant to be used in concert with the make localmodconfig step of compiling a kernel. After the database has been adequately populated, simply invoke /usr/bin/modprobed-db recall prior to compiling a kernel to load all modules followed by the make localmodconfig to do the magic.

Note: Since /usr/bin/modprobe requires root privileges, /usr/bin/modprobed-db needs to be called as root or via sudo when users wish to recall the database.

Using the Official ARCH kernel PKGBUILD

The official ARCH kernel's PKGBUILD does not have native support for this, but it is easily modified as follows:

  # get kernel version
  make prepare

  /usr/bin/modprobed-db recall         <---- insert this line
  make localmodconfig              <---- insert this line

  # load configuration
  # Configure the kernel. Replace the line below with one of your choice.
  #make menuconfig # CLI menu for configuration
  #make nconfig # new CLI menu for configuration
  #make xconfig # X-based configuration
  #make oldconfig # using old config from previous kernel version
  # ... or manually edit .config

Using Some Kernels in the AUR

Several kernel packages in the AUR have native support for modprobed-db in their PKGBUILD files. For example:

Find which other packages use it:

cd /scratch
git clone --depth 1
find /scratch/aur-mirror -iname "PKGBUILD" -print0 | xargs -0 grep "modprobed-db recall" | sort
Note: The server is rather slow and the git clone can take a while.

Alternatively, download the .tar.xz snapshot (around 90 MB) by following this link and then clicking on the latest commit message.


It is recommended that users install the package and then "use" the system for a good amount of time to allow the database to grow based on usage and capture everything the system needs before building a kernel with a make localmodconfig. Some suggested actions to allow appropriate modules to load and get cataloged:

  • Insert every kind of removable media (USB, DVD, CD, etc.)
  • Use every device on the machine (wifi, network, USB stuff like cameras, ipods, etc.)
  • Mount every kind of filesystem one might typically use including ext2/3/4, fat, vfat, CIFS shares, NFS shares, etc.
  • Use as many applications (that one would normally use) as possible in order to capture modules on which they depend. For example, IP blocking/filtering software like pgl-cliAUR.
  • Users who plan to mount iso image file should do so (this will make sure to capture the loop and isofs modules).
  • Users requiring encryption software such as truecrypt should make sure to load it, and mount some encrypted containers to ensure that the needed crypto modules are in the db.

Suggested Modules

  • cifs
  • ext2
  • ext3
  • ext4
  • fat
  • isofs
  • loop
  • vfat

Benefits of modprobed-db with make localmodconfig in custom kernels

  1. Reduced kernel footprint on FS
  2. Reduced compilation time

Comparisons using version 3.8.8-1 of the Arch kernel (from ABS):

Note: The /var/log/modprobed.db on the test machine contains 209 lines; YMMV based on specific usage and needs.
Machine CPU # of threads make localmodconfig # of Modules Modules' Size on HDD Compilation Time
Intel i7-3770K @ 4.50 GHz 8 No 3,025 129 MB 7 min 37 sec
Intel i7-3770K @ 4.50 GHz 8 Yes 230 18 MB 1 min 13 sec
Intel Q9550 @ 3.40 GHz 4 No 3,025 129 MB 14 min 21 sec
Intel Q9550 @ 3.40 GHz 4 Yes 230 18 MB 2 min 20 sec
Intel E5200 @ 3.33 GHz 2 No 3,025 129 MB 34 min 35 sec
Intel E5200 @ 3.33 GHz 2 Yes 230 18 MB 5 min 46 sec
  • 13x less modules built
  • 7x less space
  • 6x less compilation time

Number of modules found by:

find /scratch/linux-3.8 -name '*.ko' | wc -l

Size on HDD found by:

find /scratch/linux-3.8 -name '*.ko' -print0 | xargs -0 du -ch

Compilation time found by entering a preconfigured linux-3.8.8 (using stock Arch config):

$ time make -jx modules
Note: The Arch standard is to gzip each module; the numbers shown in the table above are not gzip'ed but the savings ratio will be unaffected by this.