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".
- The official documentation has multiple suggestions on how to remove kernels:
- https://help.ubuntu.com/community/RemoveOldKernels
A great recommendation is to make use of unattended-upgrades u-u (debian, ubuntu). Since version 1.0 (debian, ubuntu) u-u removes unused kernel packages by default (Remove-Unused-Kernel-Packages). Some distribution versions may not make reference or may comment out that setting in its configuration, but unless it is explicitly disabled, u-u will attempt to remove unused kernels. More info here.
For scenarios where u-u is not available or older than 1.0, kthresher is still a good option.
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.
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-grubAll 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-genericThe 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.py
chmod u+x kthresherpip
pip install kthresheror
pip install git+https://github.com/rackerlabs/kthresher.gitGithub
git clone https://github.com/rackerlabs/kthresher.git
cd kthresher && python setup.py installUsage
$ 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 up to a fixed amount of kernels and headers if available of the form "linux-(image|headers)-[0-9].*-(generic|amd64)" 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 re
import apt
import sys
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 apt.cache.LockFailedException as lfe:
print('{}, are you root?'.format(lfe))
sys.exit(1)
except SystemError:
print('Something failed')
sys.exit(1)
def get_pkg(regex):
'''Get a list of packages available that match the regex.
'''
pkgs = []
ac = apt.Cache()
ac.update()
for pkg in ac:
if re.match(regex, pkg.name):
# ignore running kernel
if pkg.name == 'linux-image-{0}'.format(uname()[2]):
continue
pkgs.append(pkg.name)
return pkgs
def main():
limit = 5
if len(sys.argv) > 1:
try:
limit = int(sys.argv[1])
except:
print("Use an integer as the limit of pkgs to install.")
sys.exit(1)
print("Installing {} kernels/headers if available...".format(limit))
kernel_regex = "^linux-image-\d\..*-(generic|amd64)$"
header_regex = "^linux-headers-\d\..*-(generic|amd64)$"
kernels = get_pkg(kernel_regex)
headers = get_pkg(header_regex)
pkgs = kernels[0:limit] + headers[0:limit]
print("Installing {} packages total\n\tkernels: {}\n\theaders: {}"
.format(len(pkgs), kernels[0:limit], headers[0:limit]))
autorm_install(pkgs)
if __name__ == "__main__":
main()Bugs
Submit Bug reports, feature requests via issues.
Logos
The art was created by Carlos Garcia <hellyeahdesign AT gmail DOT com> and released under CC BY-SA 4.0
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