kthresher

Tool to remove unused kernels that were installed automatically in Debian/Ubuntu.

This tool removes those kernel packages marked as candidate for autoremoval. Those packages are generally installed via Unattended upgrade or meta-packages.

By default, on apt 1.0 and below, the booted kernel, the latest-installed kernel and the latest kernel are set to "NeverAutoRemove". Or, for apt 1.2 and above, the booted kernel, the latest-installed kernel, the latest kernel and the second-latest kernel are set to "NeverAutoRemove".

thresher - A device that first separates the head of a stalk of grain from the straw, and then further separates the kernel from the rest of the head.

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Table of Contents

How a package is marked for autoremoval?

Whenever a package is auto-installed and there is no other dependency for it, the package is marked as a candidate for autoremoval, there is an exception if the APT configuration does have the package marked as "NeverAutoRemove".

How the kernel image is added into the "APT::NeverAutoRemove::" config?

When a kernel image is installed the postinstall script will issue the run-parts on /etc/kernel/postinst.d/ and /etc/kernel/postinst.d/${version} if any exist. The run-parts script will run each one of the scripts located in that directory, e.g.

# ls -1 /etc/kernel/postinst.d/
apt-auto-removal
initramfs-tools
update-notifier
x-grub-legacy-ec2
zz-update-grub

All the scripts found by run-parts are executed on post install of the kernel package and the output of apt-get install/upgrade/dist-upgrade will show them, e.g.

run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-96-generic /boot/vmlinuz-3.13.0-96-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-96-generic /boot/vmlinuz-3.13.0-96-generic
run-parts: executing /etc/kernel/postinst.d/update-notifier 3.13.0-96-generic /boot/vmlinuz-3.13.0-96-generic
run-parts: executing /etc/kernel/postinst.d/x-grub-legacy-ec2 3.13.0-96-generic /boot/vmlinuz-3.13.0-96-generic
run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.13.0-96-generic /boot/vmlinuz-3.13.0-96-generic

The first script "apt-auto-removal" takes care of adding a configuration in /etc/apt/apt.conf.d/01autoremove-kernels this script generates that list based on the logic described above, it means that the NeverAutoRemove may have anything between two to three kernels listed.

Supported Operating Systems

Installation

script

wget -O kthresher https://raw.githubusercontent.com/rackerlabs/kthresher/master/kthresher/kthresher.py
chmod u+x kthresher

pip

pip install kthresher

or

pip install git+https://github.com/rackerlabs/kthresher.git

Github

git clone https://https://github.com/rackerlabs/kthresher.git
cd kthresher && python setup.py install

Usage

$ kthresher -h
usage: kthresher [-h] [-c FILE] [-d] [-H] [-k [N]] [-p] [-s] [-v] [-V]

Purge Unused Kernels.

optional arguments:
  -h, --help            show this help message and exit
  -c FILE, --config FILE
                        Config file, default is /etc/kthresher.conf
  -d, --dry-run         List unused kernel images available to purge(dry run).
                        Is always verbose.
  -H, --headers         Include the search for kernel headers.
  -k [N], --keep [N]    Number of kernels to keep, default 1.
  -p, --purge           Purge Unused Kernels.
  -s, --show-autoremoval
                        Show kernel packages available for autoremoval.
  -v, --verbose         Be verbose.
  -V, --version         Print version.

Examples

List which kernel images and its dependencies would remove(dry run)

# kthresher -d
INFO: Attempting to read /etc/kthresher.conf.
INFO: Config file /etc/kthresher.conf is empty or does not exist, ignoring.
INFO: Options: {'purge': False, 'verbose': False, 'dry_run': True, 'keep': 1}
INFO: ----- DRY RUN -----
INFO: Running kernel is linux-image-3.13.0-83-generic v[3.13.0-83.127]
INFO: Attempting to keep 1 kernel package(s)
INFO: Found 4 kernel image(s) installed and available for autoremoval
INFO: Pre-sorting: ['3.16.0-60.80~14.04.1', '3.13.0-77.121', '3.13.0-63.103', '3.16.0-33.44~14.04.1']
INFO: Post-sorting: ['3.13.0-63.103', '3.13.0-77.121', '3.16.0-33.44~14.04.1', '3.16.0-60.80~14.04.1']
INFO:   Purging packages from version: 3.13.0-63.103
INFO:           Purging: linux-image-extra-3.13.0-63-generic
INFO:           Purging: linux-image-3.13.0-63-generic
INFO:   Purging packages from version: 3.13.0-77.121
INFO:           Purging: linux-image-3.13.0-77-generic
INFO:           Purging: linux-image-extra-3.13.0-77-generic
INFO:   Purging packages from version: 3.16.0-33.44~14.04.1
INFO:           Purging: linux-image-3.16.0-33-generic

Show all kernel packages available for autoremoval

# kthresher -s
List of kernel packages available for autoremoval:
               Version Package
          3.13.0.83.89 linux-generic
          3.13.0-51.84 linux-headers-3.13.0-51
          3.13.0-51.84 linux-headers-3.13.0-51-generic
         3.13.0-71.114 linux-headers-3.13.0-71
         3.13.0-71.114 linux-headers-3.13.0-71-generic
         3.13.0-77.121 linux-headers-3.13.0-77
         3.13.0-77.121 linux-headers-3.13.0-77-generic
         3.13.0-79.123 linux-headers-3.13.0-79
         3.13.0-79.123 linux-headers-3.13.0-79-generic
         3.13.0-63.103 linux-image-3.13.0-63-generic
         3.13.0-77.121 linux-image-3.13.0-77-generic
  3.16.0-33.44~14.04.1 linux-image-3.16.0-33-generic
  3.16.0-60.80~14.04.1 linux-image-3.16.0-60-generic
         3.13.0-63.103 linux-image-extra-3.13.0-63-generic
         3.13.0-77.121 linux-image-extra-3.13.0-77-generic
          3.13.0.83.89 linux-image-generic

Purge Unused Kernels, keep 3 kernels and be verbose

# kthresher -p -k3 v
INFO: Attempting to read /etc/kthresher.conf.
INFO: Config file /etc/kthresher.conf is empty or does not exist, ignoring.
INFO: Options: {'purge': True, 'verbose': True, 'dry_run': False, 'keep': 3}
INFO: Running kernel is linux-image-3.13.0-83-generic v[3.13.0-83.127]
INFO: Attempting to keep 3 kernel package(s)
INFO: Found 4 kernel image(s) installed and available for autoremoval
INFO: Pre-sorting: ['3.16.0-60.80~14.04.1', '3.13.0-77.121', '3.13.0-63.103', '3.16.0-33.44~14.04.1']
INFO: Post-sorting: ['3.13.0-63.103', '3.13.0-77.121', '3.16.0-33.44~14.04.1', '3.16.0-60.80~14.04.1']
INFO:   Purging packages from version: 3.13.0-63.103
INFO:           Purging: linux-image-extra-3.13.0-63-generic
INFO:           Purging: linux-image-3.13.0-63-generic
Fetched 0 B in 0s (0 B/s)
(Reading database ... 169514 files and directories currently installed.)
Removing linux-image-extra-3.13.0-63-generic (3.13.0-63.103) ...
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
update-initramfs: Generating /boot/initrd.img-3.13.0-63-generic
run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.16.0-60-generic
Found initrd image: /boot/initrd.img-3.16.0-60-generic
Found linux image: /boot/vmlinuz-3.16.0-33-generic
Found initrd image: /boot/initrd.img-3.16.0-33-generic
Found linux image: /boot/vmlinuz-3.13.0-83-generic
Found initrd image: /boot/initrd.img-3.13.0-83-generic
Found linux image: /boot/vmlinuz-3.13.0-77-generic
Found initrd image: /boot/initrd.img-3.13.0-77-generic
Found linux image: /boot/vmlinuz-3.13.0-63-generic
Found initrd image: /boot/initrd.img-3.13.0-63-generic
done
Purging configuration files for linux-image-extra-3.13.0-63-generic (3.13.0-63.103) ...
Removing linux-image-3.13.0-63-generic (3.13.0-63.103) ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
update-initramfs: Deleting /boot/initrd.img-3.13.0-63-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.16.0-60-generic
Found initrd image: /boot/initrd.img-3.16.0-60-generic
Found linux image: /boot/vmlinuz-3.16.0-33-generic
Found initrd image: /boot/initrd.img-3.16.0-33-generic
Found linux image: /boot/vmlinuz-3.13.0-83-generic
Found initrd image: /boot/initrd.img-3.13.0-83-generic
Found linux image: /boot/vmlinuz-3.13.0-77-generic
Found initrd image: /boot/initrd.img-3.13.0-77-generic
done
Purging configuration files for linux-image-3.13.0-63-generic (3.13.0-63.103) ...
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 3.13.0-63-generic /boot/vmlinuz-3.13.0-63-generic

Verbose run using a non-default config file

# kthresher -c myconf.conf
INFO: Attempting to read myconf.conf.
INFO: Options found: ['keep', 'dry_run'].
INFO: Valid setting found "keep"
INFO:   keep = 1
INFO: Valid setting found "dry_run"
INFO:   dry_run = True
INFO: Options: {'purge': False, 'verbose': True, 'dry_run': True, 'keep': 1}
INFO: ----- DRY RUN -----
INFO: Running kernel is linux-image-3.13.0-83-generic v[3.13.0-83.127]
INFO: Attempting to keep 1 kernel package(s)
INFO: Found 2 kernel image(s) installed and available for autoremoval
INFO: Pre-sorting: ['3.16.0-60.80~14.04.1', '3.16.0-33.44~14.04.1']
INFO: Post-sorting: ['3.16.0-33.44~14.04.1', '3.16.0-60.80~14.04.1']
INFO:   Purging packages from version: 3.16.0-33.44~14.04.1
INFO:           Purging: linux-image-3.16.0-33-generic

Content of myconf.conf is: .. code-block:

[main]
keep    = 1
dry_run = yes
#purge = yes

Dry run including headers

# kthresher -v -d -H
INFO: Attempting to read /etc/kthresher.conf.
INFO: Options found: ['keep', 'dry_run', 'purge', 'verbose'].
INFO: Valid setting found "keep"
INFO:   keep = 2
INFO: Valid setting found "dry_run"
INFO:   dry_run = False
INFO: Valid setting found "purge"
INFO:   purge = True
INFO: Valid setting found "verbose"
INFO:   verbose = True
INFO: Options: {'verbose': True, 'dry_run': True, 'keep': 2, 'purge': True, 'headers': True}
INFO: ----- DRY RUN -----
INFO: Running kernel is linux-image-3.13.0-83-generic v[3.13.0-83.127]
INFO: Attempting to keep 2 kernel package(s)
INFO: Found 4 kernel image(s) installed and available for autoremoval
INFO: Pre-sorting: ['3.16.0-60.80~14.04.1', '3.16.0-33.44~14.04.1', '3.13.0-85.129', '3.13.0-79.123']
INFO: Post-sorting: ['3.13.0-79.123', '3.13.0-85.129', '3.16.0-33.44~14.04.1', '3.16.0-60.80~14.04.1']
INFO:   Purging packages from version: 3.13.0-79.123
INFO:           Purging: linux-image-3.13.0-79-generic
INFO:           Purging: linux-headers-3.13.0-79-generic
INFO:           Purging: linux-headers-3.13.0-79
INFO:   Purging packages from version: 3.13.0-85.129
INFO:           Purging: linux-image-3.13.0-85-generic
INFO:           Purging: linux-headers-3.13.0-85
INFO:           Purging: linux-headers-3.13.0-85-generic

Testing

The below code can be used to install all the kernels and headers available of the form "linux-(image|headers)-[0-9].*-generic" at the end it should end up with two or three kernels in the NeverAutoRemove list, including the latest, the prior to latest and the running kernel.

#!/usr/bin/env python
'''Installs available linux-image-* and linux-headers-*
And set them for autoremoval, so kthresher can be used for testing.
'''

import apt
import re
from platform import uname

def autorm_install(pkgs):
    '''Install a list of packages and set them autoremovable.
    '''
    latest_kernel = ''
    ac = apt.Cache()
    for pkg in pkgs:
        latest_kernel = pkg
        k = ac[pkg]
        if not k.is_installed:
            k.mark_install(from_user=False)
    try:
        ac.commit(install_progress=None)
    except SystemError:
        print('Something failed')
        sys.exit(1)

def get_kernels():
    '''Get a list of all the kernels/headers available of the form:
    linux-image-* and linux-headers-*
    and install them.
    '''
    kernels = []
    ac = apt.Cache()
    ac.update()
    for pkg in ac:
        if re.match("^linux-(image|headers)-\d\..*-generic$", pkg.name):
            if not pkg.name == 'linux-image-{0}'.format(uname()[2]):
                kernels.append(pkg.name)
    return kernels

def main():
    kernels = get_kernels()
    autorm_install(kernels)

if __name__ == "__main__":
    main()

Known Issues

Python3 support is currently broken due to a known disutils.LooseVersion issue.

Bugs

Submit Bug reports, feature requests via issues.