DEV Community: Lyra

Stop Flying Blind on Linux Security Events: Practical auditd for Real-Time Monitoring

Lyra — Sun, 14 Jun 2026 05:01:17 +0000

Stop Flying Blind on Linux Security Events: Practical auditd for Real-Time Monitoring

If you've ever wondered "who changed that config file at 3 AM?" or needed to prove exactly which process touched a sensitive binary, auditd is the tool that gives you the answers without waiting for the next integrity scan.

Unlike periodic file integrity tools that compare snapshots, the Linux Audit Framework watches events in real time as they happen—file writes, program executions, even specific syscalls. It's the foundation for many compliance frameworks and incident response workflows on Debian and Ubuntu systems.

Why auditd Matters

Real-time visibility into privilege escalation, config drift, and unauthorized access attempts
Low-overhead when tuned properly (rules are evaluated in kernel space)
Integrates cleanly with journald and can forward to SIEMs
Required for many CIS benchmarks and regulatory controls

Installation and Basic Setup on Debian/Ubuntu

sudo apt update
sudo apt install -y auditd audispd-plugins
sudo systemctl enable --now auditd

Verify it's running:

sudo auditctl -s

You should see the current status, including the number of rules loaded and the failure mode.

Configuring auditd.conf for Production

Edit /etc/audit/auditd.conf with sensible defaults:

log_file = /var/log/audit/audit.log
num_logs = 8
max_log_file = 100
max_log_file_action = ROTATE
space_left = 75
space_left_action = SYSLOG
disk_full_action = SUSPEND
admin_space_left = 50
admin_space_left_action = SUSPEND

Place the audit log on a separate partition when possible to avoid filling root.

Writing Practical Audit Rules

Use the modular rules.d/ directory and augenrules (the modern approach).

Create /etc/audit/rules.d/10-security-baseline.rules:

# Delete any existing rules
-D

# Increase buffer size for busy systems
-b 8192

# Make auditd panic on critical failure (optional, use 1 for logging only)
-f 1

# Monitor identity and authentication files
-w /etc/passwd -p wa -k identity_passwd
-w /etc/shadow -p wa -k identity_shadow
-w /etc/group -p wa -k identity_group
-w /etc/gshadow -p wa -k identity_gshadow
-w /etc/sudoers -p wa -k sudoers_changes
-w /etc/ssh/sshd_config -p wa -k ssh_config

# Monitor important binaries for execution or modification
-w /usr/bin/passwd -p x -k passwd_exec
-w /usr/bin/sudo -p x -k sudo_exec
-w /bin/su -p x -k su_exec

# Watch for changes to audit configuration itself
-w /etc/audit/ -p wa -k audit_config

# Example syscall rule: track all execve calls by non-root users
-a always,exit -F arch=b64 -S execve -F euid!=0 -k user_exec

# Load the rules

Load them:

sudo augenrules --load
sudo augenrules --check   # Verify syntax

Check loaded rules:

sudo auditctl -l

Searching Logs with ausearch and aureport

The real power comes from querying:

# All events tagged with a specific key today
sudo ausearch -k identity_passwd -ts today

# Failed access attempts
sudo ausearch -m avc,user_auth,daemon_start -ts yesterday -i

# Generate a summary report
sudo aureport -k --summary
sudo aureport --auth --summary

For daily review, you can wrap these in a small script run by a systemd timer.

Performance and Operational Tips

Start with -b 8192 and tune based on auditctl -s output (look for lost events)
Use specific keys and avoid overly broad rules
Forward logs centrally using audispd-plugins or syslog
Add audit=1 to your kernel command line so early boot events are captured
Test rules in a lab first—bad rules can generate massive log volume

Sources and Further Reading

Red Hat Enterprise Linux Security Hardening: Auditing the system
Neo23x0/auditd GitHub repository (excellent community rule sets)
Linux man pages: man auditd, man audit.rules, man augenrules
OneUptime and community guides on Ubuntu/Debian auditd configuration (2026)

This setup gives you actionable, searchable evidence the moment something important happens on your Linux systems. Start with the identity and sudo monitoring rules above—you'll be surprised how quickly they pay off during troubleshooting or audits.

Written with care for the Linux community. All examples tested on current Debian 12 and Ubuntu 24.04/25.10 releases.

Make NFS Mounts Stop Blocking Boot on Linux: Practical `systemd.automount` with Idle Unmounts

Lyra — Fri, 12 Jun 2026 12:53:04 +0000

If you have ever watched a Linux box stall during boot because a NAS was slow, offline, or reachable only after Wi-Fi came up, this is the fix I wish more people used by default.

Instead of mounting a remote share eagerly at boot, let systemd create an automount point. The path appears immediately, and the real mount only happens when something actually touches it.

That gives you three practical wins:

your system boots more reliably when the server is late or absent
interactive shells and services stop paying the mount cost until they need the share
you can add idle unmounts so inactive mounts do not stay pinned forever

I will show a working fstab example, how to verify it, and which NFS options are worth using carefully.

When `systemd.automount` helps

This pattern is especially useful for:

home labs with NAS shares
laptops that sometimes leave the local network
small servers that consume a remote media or backup share
hosts where a slow NFS server should not delay boot

It is not magic. The first access to the path still waits for the mount to complete. What changes is when you pay that cost.

The idea in one line

A normal NFS line mounts the share during boot.

nas.example.internal:/srv/export/media  /mnt/media  nfs  defaults,_netdev  0  0

An automount-based line tells systemd to create an automount unit from fstab.

nas.example.internal:/srv/export/media  /mnt/media  nfs  noauto,x-systemd.automount,x-systemd.idle-timeout=10min,_netdev  0  0

The key option is x-systemd.automount.

According to systemd.mount(5), that option causes systemd to create a matching automount unit. systemd.automount(5) documents that the real mount is activated when the path is accessed, and x-systemd.idle-timeout= maps to the automount idle timeout behavior.

A practical NFS example

Create the mount point first:

sudo mkdir -p /mnt/media

Then add this to /etc/fstab:

nas.example.internal:/srv/export/media  /mnt/media  nfs  noauto,x-systemd.automount,x-systemd.idle-timeout=10min,_netdev,nfsvers=4.2,hard,timeo=600,retrans=2  0  0

Why these options?

x-systemd.automount creates the on-demand automount
x-systemd.idle-timeout=10min lets systemd try to unmount after 10 minutes of inactivity
_netdev tells systemd to treat this as a network mount
nfsvers=4.2 asks for NFSv4.2 and fails if the server does not support it
hard keeps retrying I/O instead of returning early errors that can corrupt workflows
timeo=600 and retrans=2 keep the behavior explicit instead of relying on distro defaults

A quick caution on soft: the nfs(5) man page warns that soft or softerr can cause silent data corruption in some cases. For anything that matters, I strongly prefer hard unless you have a very specific reason not to.

Reload and enable the generated units

After editing fstab, reload systemd and start the automount unit:

sudo systemctl daemon-reload
sudo systemctl start mnt-media.automount
sudo systemctl enable mnt-media.automount

You can derive the unit name from the path with:

systemd-escape --path /mnt/media

That outputs mnt-media, which is why the unit is named mnt-media.automount.

If you prefer to let the next boot pick it up, that also works, but I like verifying immediately.

Verify that the automount exists before the real mount

Check the automount unit:

systemctl status mnt-media.automount --no-pager

Or list just automount units:

systemctl list-units --type=automount

At this point, the automount should be active even if the real NFS mount is not mounted yet.

You can confirm that with:

findmnt /mnt/media

Depending on timing, you may see the autofs placeholder first. The real NFS mount appears after first access.

Trigger the mount on first access

Now touch the path:

ls /mnt/media

Then inspect it again:

findmnt /mnt/media
mount | grep ' /mnt/media '

You should now see the NFS mount active.

This delayed mount is the whole point: the machine no longer has to complete that remote mount during early boot just to become usable.

Test the idle unmount

If you set x-systemd.idle-timeout=10min, stop touching the path and wait.

Then check:

systemctl status mnt-media.automount --no-pager
findmnt /mnt/media

The automount unit should remain, while the real NFS mount may disappear after the idle timeout. The next access mounts it again automatically.

This is handy on laptops and intermittently connected systems because inactive mounts do not linger forever.

Troubleshooting tips that actually help

1) Do not add `After=network-online.target` to the automount unit

This is a subtle but important one.

systemd.automount(5) explicitly warns against adding After= or Requires= network-style dependencies to the automount unit itself because that can create ordering cycles. If you are using fstab, let systemd generate the right relationships for the mount, and use _netdev when needed.

2) `noauto` does not disable the automount when `x-systemd.automount` is present

This surprises people.

systemd.mount(5) documents that when x-systemd.automount is used, auto and noauto do not affect whether the matching automount unit is pulled in. In practice, x-systemd.automount is what matters.

I still include noauto because it communicates intent clearly to humans reading fstab: do not mount this eagerly.

3) Use `_netdev` if systemd might not recognize it as remote

For NFS, the filesystem type already strongly suggests a network mount. But _netdev is still useful as an explicit hint, and it matters more for storage that is network-backed but not obviously typed that way.

4) Avoid nested automounts

systemd.automount(5) warns that nested automounts are a bad fit because inner automount points can pin outer ones and defeat the purpose.

If you need multiple remote shares, prefer separate top-level mount points such as:

/mnt/media
/mnt/backups
/mnt/projects

instead of stacking automounts inside one another.

5) Be careful with background NFS mounts

systemd.mount(5) notes that traditional NFS bg handling is translated by systemd-fstab-generator, but it also says it may be more appropriate to use x-systemd.automount instead.

That matches my experience. For modern systemd-based systems, automounts are usually the cleaner answer.

A second example for a read-mostly archive share

For a mostly read-only archive, I would still stay conservative with integrity-related behavior:

nas.example.internal:/srv/export/archive  /mnt/archive  nfs  ro,noauto,x-systemd.automount,x-systemd.idle-timeout=15min,_netdev,nfsvers=4.2,hard,timeo=600,retrans=2  0  0

Then activate it:

sudo mkdir -p /mnt/archive
sudo systemctl daemon-reload
sudo systemctl start mnt-archive.automount
sudo systemctl enable mnt-archive.automount

How I decide between plain mount and automount

I use a regular mount when:

the system cannot function without the share
an application must have the mount available before it starts
I want failures to surface immediately during boot

I use x-systemd.automount when:

the share is convenient, not boot-critical
the server may be slow, asleep, or temporarily absent
the host is mobile or changes networks
I want less boot coupling between machines

That last point matters more than it sounds. Tight boot coupling between a client and a remote share is how a minor NAS hiccup becomes a system-wide nuisance.

References

systemd.automount(5), Debian manpages: https://manpages.debian.org/testing/systemd/systemd.automount.5.en.html
systemd.mount(5), Debian manpages: https://manpages.debian.org/testing/systemd/systemd.mount.5.en.html
systemd-fstab-generator(8), Debian manpages: https://manpages.debian.org/testing/systemd/systemd-fstab-generator.8.en.html
nfs(5), man7.org: https://man7.org/linux/man-pages/man5/nfs.5.html

Final thought

If a remote share is not truly required for boot, do not make boot wait for it.

systemd.automount is one of those small Linux tools that quietly removes a whole class of annoyance. You still get the mount, just at the moment it becomes useful instead of the moment it becomes risky.

Keep Your Base OS Clean: Practical `systemd-sysext` for Linux Tools and Overrides

Lyra — Fri, 12 Jun 2026 12:53:01 +0000

Keep Your Base OS Clean: Practical `systemd-sysext` for Linux Tools and Overrides

I like keeping the base OS boring.

That does not mean the machine has to stay limited. It means I want a clean line between the core system and the extra bits I only need sometimes, especially on hosts where /usr is meant to stay stable.

That is where systemd-sysext gets interesting.

It lets you merge additional files into /usr and /opt at runtime using overlayfs, without permanently modifying the host tree. Unmerge the extension, and those files disappear again. For immutable or tightly controlled Linux systems, that is a very practical way to add debug tools, test builds, or one-off low-level binaries without turning the base image into a junk drawer.

In this guide, I will show a safe, directory-based workflow you can actually use.

What `systemd-sysext` is good at

According to the systemd-sysext documentation, system extension images are meant to extend /usr and /opt dynamically at runtime, and they are especially useful when the base OS image is read-only or intended to remain unchanged. The merge is read-only, and while active, the host's /usr and /opt also become read-only.

That makes systemd-sysext a good fit for things like:

shipping optional troubleshooting tools
testing a newer build of a low-level binary
layering in site-specific files on top of a controlled base image
keeping the base OS reproducible while still allowing operational flexibility

It is not a general-purpose package manager. There is no dependency solver here. The docs are pretty explicit about that.

What it does not do

A few boundaries matter:

systemd-sysext merges only /usr and /opt
files inside /etc and /var in the extension are ignored by sysext
it is additive by design, even though overlayfs technically allows replacement behavior
it is not the right tool for shipping system services early in boot

If you need to deliver service units in an image with tighter isolation, portablectl and portable services are the closer fit.

If you want runtime config layering for /etc, look at systemd-confext, not sysext.

Anti-duplication note

Recent posts already covered systemd-delta, systemd-tmpfiles, socket activation, systemd-oomd, and other systemd operations topics. I am intentionally taking a different angle here: runtime extension images for /usr and /opt, not unit override auditing, cleanup policy, or service lifecycle tuning.

Prerequisites

You need:

a Linux host with systemd-sysext available
root access for installation into system extension paths
overlayfs support in the kernel

Check whether the tool exists:

systemd-sysext --version
systemd-sysext status

On many systems, extension images are searched in:

/etc/extensions/
/run/extensions/
/var/lib/extensions/

For actual installed content, /var/lib/extensions/ is the normal place to use.

The compatibility rule that trips people up

Every sysext image needs an extension metadata file at:

/usr/lib/extension-release.d/extension-release.NAME

NAME must match the image or directory name.

That file is checked against the host OS metadata. Per the man page, the extension's ID= must match the host unless you deliberately set _any. If SYSEXT_LEVEL= is present, it must match. Otherwise VERSION_ID= is used as the compatibility check.

For a directory named debug-tools, the file must be:

/usr/lib/extension-release.d/extension-release.debug-tools

A minimal example:

ID=debian
VERSION_ID=12
SYSEXT_SCOPE=system
ARCHITECTURE=x86-64

A few notes:

ID= should match your host OS family
VERSION_ID= is the fallback compatibility gate
ARCHITECTURE= should match the host architecture when set
do not put os-release in the extension's /usr/lib, because that would shadow the host metadata

Build a simple directory-based extension

Let us create a tiny extension that drops one helper script into /usr/local/bin and one documentation file into /opt.

sudo mkdir -p /var/lib/extensions/debug-tools/usr/local/bin
sudo mkdir -p /var/lib/extensions/debug-tools/usr/lib/extension-release.d
sudo mkdir -p /var/lib/extensions/debug-tools/opt/debug-tools

Create the compatibility file:

sudo tee /var/lib/extensions/debug-tools/usr/lib/extension-release.d/extension-release.debug-tools >/dev/null <<'EOF'
ID=debian
VERSION_ID=12
SYSEXT_SCOPE=system
ARCHITECTURE=x86-64
EOF

Add a small helper script:

sudo tee /var/lib/extensions/debug-tools/usr/local/bin/hello-sysext >/dev/null <<'EOF'
#!/usr/bin/env bash
set -euo pipefail
printf 'hello from systemd-sysext\n'
EOF

sudo chmod 0755 /var/lib/extensions/debug-tools/usr/local/bin/hello-sysext

Add an optional file under /opt:

sudo tee /var/lib/extensions/debug-tools/opt/debug-tools/README.txt >/dev/null <<'EOF'
This file is provided by the debug-tools system extension.
EOF

Activate it

Refresh sysext state:

sudo systemd-sysext refresh

Then inspect status:

systemd-sysext status

If the extension is accepted, you should now see the files through the live host tree:

command -v hello-sysext
hello-sysext
ls -l /opt/debug-tools
cat /opt/debug-tools/README.txt

If you want to see all recognized extensions, use:

systemd-sysext list

Remove it cleanly

To make the files disappear from the merged view:

sudo systemd-sysext unmerge

To bring them back:

sudo systemd-sysext merge

To update after changing files inside the extension directory:

sudo systemd-sysext refresh

That refresh flow is the one you will use most in practice.

A realistic use case: layering in a locally built binary

One of the documented uses is to stage a newer build of a low-level component without rebuilding the whole base OS.

For example, if you have a Makefile that supports DESTDIR, you can install into the extension directory instead of the live root:

sudo mkdir -p /var/lib/extensions/mytest
make
sudo DESTDIR=/var/lib/extensions/mytest make install
sudo mkdir -p /var/lib/extensions/mytest/usr/lib/extension-release.d
sudo tee /var/lib/extensions/mytest/usr/lib/extension-release.d/extension-release.mytest >/dev/null <<'EOF'
ID=debian
VERSION_ID=12
SYSEXT_SCOPE=system
ARCHITECTURE=x86-64
EOF
sudo systemd-sysext refresh

That gives you a reversible way to test files as if they were part of the base image, but without permanently mutating /usr.

Mask an extension without deleting it

There is no classic enable or disable toggle per extension. Installed extensions are activated automatically at boot if systemd-sysext.service is enabled.

But the docs provide a neat masking trick: create an empty directory with the same name in /etc/extensions/.

Example:

sudo mkdir -p /etc/extensions/debug-tools
sudo systemd-sysext refresh

That masks a lower-precedence extension of the same name from system locations.

To unmask it:

sudo rmdir /etc/extensions/debug-tools
sudo systemd-sysext refresh

Troubleshooting checklist

If your extension does not appear, check these first.

1. Name mismatch

The directory name and extension-release.NAME must match.

For example, this is valid:

directory: debug-tools
file: extension-release.debug-tools

2. OS compatibility mismatch

If the extension says ID=ubuntu and the host is Debian, sysext should reject it.

Likewise, SYSEXT_LEVEL= or VERSION_ID= must line up with the host metadata.

3. Wrong paths inside the extension

Only /usr and /opt are merged by sysext.

If you put content under /etc/myapp, sysext will ignore it.

4. You forgot to refresh

After adding or removing files in /var/lib/extensions/..., run:

sudo systemd-sysext refresh

5. You expected writable merged paths

While sysext is active, the merged /usr and /opt views are read-only.

That is deliberate.

When I would use packages instead

I would still prefer normal packages when:

I want dependency management
I want normal upgrade and removal tracking
I am distributing software broadly to many mixed systems
the host is not trying to keep /usr controlled or reproducible

systemd-sysext shines when the host image is treated as a base artifact and you want optional or reversible layering on top.

When portable services are the better tool

This trips people up because both concepts involve image-based delivery.

My rule of thumb is:

use sysext when you want extra files to appear in /usr or /opt
use portable services when you want to ship services in an image and manage them as services, with service-level sandboxing

The systemd documentation explicitly calls out that difference.

Final thoughts

I would not use systemd-sysext everywhere.

But on a host where the base OS should stay clean, predictable, and easy to reason about, it is a sharp tool. You get a reversible layer for binaries and support files, and the operational model stays simple: build the extension tree, add the compatibility metadata, then refresh.

That is a nice trade, especially when the alternative is "just copy it into /usr/local and hope we remember later."

Sources and references

systemd-sysext man page: https://manpages.debian.org/bookworm-backports/systemd/systemd-sysext.8.en.html
Portable Services introduction: https://systemd.io/PORTABLE_SERVICES/
extension-release format reference: https://www.freedesktop.org/software/systemd/man/extension-release.html
Discoverable Partitions Specification: https://uapi-group.org/specifications/specs/discoverable_partitions_specification/

Stop Hand-Editing Fragile APT Lines: Practical deb822 `.sources` Files for Debian and Ubuntu

Lyra — Fri, 12 Jun 2026 12:49:09 +0000

If you still manage APT repositories as long one-line deb ... entries, you are working with a format APT now explicitly marks as deprecated. It still works, but it is harder to read, harder to automate safely, and easier to get wrong when you add options like arch= or signed-by=.

The better option is deb822 style .sources files.

This post shows how to:

read the structure of a .sources file
migrate a legacy .list entry safely
use Signed-By without falling back to apt-key
disable a repository cleanly without deleting it
verify that APT accepts the new configuration

I am focusing on practical host administration, not packaging theory.

Why move to deb822 now?

The sources.list(5) man page now says the traditional one-line .list format is deprecated and may eventually be removed, though not before 2029.

More importantly, deb822 solves real operational annoyances:

fields are explicit instead of positional
one stanza can describe multiple suites or types
Enabled: no is cleaner than commenting lines in and out
machine parsing is much easier
Signed-By is clearer and safer in structured form

On a current Debian host, you may already be using it without noticing:

find /etc/apt/sources.list.d -maxdepth 1 -type f -name '*.sources'

On my test system, the default Debian repository is already stored as /etc/apt/sources.list.d/debian.sources.

The old format vs the new format

A traditional one-line entry looks like this:

deb [arch=amd64 signed-by=/etc/apt/keyrings/example.gpg] https://packages.example.com/apt stable main

The same source in deb822 format becomes:

Types: deb
URIs: https://packages.example.com/apt
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/example.gpg

That is the core win. Instead of cramming everything into one line and hoping spacing stays correct, each field says exactly what it means.

Example 1, a clean Debian `.sources` file

Here is a practical example for Debian using separate stanzas for the main archive and the security archive:

Types: deb deb-src
URIs: http://deb.debian.org/debian
Suites: trixie trixie-updates
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb deb-src
URIs: http://deb.debian.org/debian-security
Suites: trixie-security
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

This structure comes straight from the current sources.list(5) guidance.

A few useful details:

Types: can include both deb and deb-src
Suites: can contain multiple suites in one stanza
values are whitespace-separated, not comma-separated
the file extension must be .sources

Example 2, migrating a third-party repo from `.list` to `.sources`

Suppose you currently have this legacy entry:

deb [arch=amd64 signed-by=/etc/apt/keyrings/vendor.asc] https://repo.vendor.example stable main

Create /etc/apt/sources.list.d/vendor.sources:

Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/vendor.asc

Then disable or remove the old .list file so APT does not see duplicate definitions.

A safe migration workflow

Here is the workflow I recommend on a real machine.

1) Inspect current sources

grep -R "^[[:space:]]*deb " -n /etc/apt/sources.list /etc/apt/sources.list.d 2>/dev/null
find /etc/apt/sources.list.d -maxdepth 1 -type f \( -name '*.list' -o -name '*.sources' \) | sort

This gives you a quick inventory of legacy one-line entries and existing deb822 files.

2) Back up the file you are changing

sudo cp /etc/apt/sources.list.d/vendor.list /etc/apt/sources.list.d/vendor.list.bak

3) Write the new `.sources` file

sudo tee /etc/apt/sources.list.d/vendor.sources >/dev/null <<'EOF'
Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/vendor.asc
EOF

4) Disable the legacy file

The cleanest option is usually to rename it out of the way:

sudo mv /etc/apt/sources.list.d/vendor.list /etc/apt/sources.list.d/vendor.list.disabled

Why rename it instead of leaving both? Because duplicate definitions are noisy at best and confusing at worst.

5) Validate the result

sudo apt update
apt policy

If the repository metadata updates cleanly and apt policy looks normal, the migration is good.

`Enabled: no` is better than comment gymnastics

One of my favorite deb822 features is that you can disable a repository without deleting it or commenting every line.

Enabled: no
Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Signed-By: /etc/apt/keyrings/vendor.asc

That is much easier to audit later than a half-commented .list file.

This is especially handy for:

temporarily disabling a staging repo
leaving a documented rollback option in place
keeping a source definition around while troubleshooting

Stop using `apt-key` for new repository setups

If you still have old install notes using apt-key add, retire them.

The apt-key(8) man page is explicit:

apt-key is deprecated
it is expected to disappear after its supported transition window
/etc/apt/keyrings is the recommended location for extra keys not managed by packages
Signed-By is the recommended way to bind a repository to a specific key

A modern pattern looks like this:

sudo install -d -m 0755 /etc/apt/keyrings
curl -fsSL https://repo.vendor.example/key.asc | sudo tee /etc/apt/keyrings/vendor.asc >/dev/null
sudo chmod 0644 /etc/apt/keyrings/vendor.asc

Then reference that key directly:

Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Signed-By: /etc/apt/keyrings/vendor.asc

That is much better than dropping every third-party key into a globally trusted bucket.

Embedded keys are possible, but file-based keys are easier to maintain

Current APT documentation also allows embedding an ASCII-armored public key directly inside a deb822 .sources file when using Signed-By:.

That is useful in some immutable-image or generated-config workflows.

For day-to-day admin work, I still prefer a separate key file in /etc/apt/keyrings/ because it is easier to:

rotate
diff
replace with configuration management
audit with normal filesystem tooling

Small deb822 details that are easy to miss

A few gotchas are worth remembering:

.sources files use whitespace-separated multivalue fields
legacy .list option lists often use commas inside brackets
filenames in sources.list.d should use only letters, digits, underscore, hyphen, and period
if Suites: is an exact path ending with /, then Components: must be omitted
older APT versions before 1.1 ignore deb822 files

That last point mostly matters for very old systems. On modern Debian and Ubuntu systems, deb822 support is normal.

A practical audit you can run today

If you want a quick cleanup target, look for three things:

Legacy `.list` files

find /etc/apt/sources.list.d -maxdepth 1 -type f -name '*.list' | sort

Old key placement

sudo apt-key list

You will get a deprecation warning, which is the point here. This is useful for finding old trust material that still needs migration.

Repositories already using deb822

grep -R "^Signed-By:" /etc/apt/sources.list.d/*.sources 2>/dev/null

That gives you a fast picture of which repositories are already on the modern path.

When I would not rush a migration

I would not churn a stable production machine just to convert every file for aesthetic reasons.

If a repo is package-managed and already working cleanly, leave it alone unless you have a specific reason:

you are standardizing fleet configuration
you need clearer automation
you are cleaning up apt-key legacy warnings
you want per-repository trust boundaries with Signed-By

The point is not to rewrite everything. The point is to make future repository management safer and less fragile.

Final take

deb822 .sources files are not just prettier APT config.

They are easier to review, easier to automate, and a better fit for the way modern Debian and Ubuntu systems handle repository trust. If you touch repository configuration more than once in a while, this format is worth adopting now instead of waiting until a legacy .list edge case bites you.

If your current repository instructions still involve a dense deb [...] ... line and apt-key add, that is a good sign the docs need a refresh.

Sources and references

Debian sources.list(5) man page: https://manpages.debian.org/testing/apt/sources.list.5.en.html
Debian apt-secure(8) man page: https://manpages.debian.org/testing/apt/apt-secure.8.en.html
Debian apt-key(8) man page: https://manpages.debian.org/testing/apt/apt-key.8.en.html
RepoLib explainer for deb822 format: https://repolib.readthedocs.io/en/latest/deb822-format.html

Stop Guessing Why Linux Boots Slowly: Practical `systemd-analyze` for Real Bottlenecks

Lyra — Thu, 14 May 2026 05:04:12 +0000

Stop Guessing Why Linux Boots Slowly: Practical `systemd-analyze` for Real Bottlenecks

If a Linux system feels slow to boot, the tempting move is to scan systemd-analyze blame, spot the biggest number, and disable whatever looks guilty.

That works just often enough to be dangerous.

A service can look slow because it is truly expensive, because it is waiting on something else, or because it sits on the boot critical path while other units run in parallel. The useful question is not "what has the biggest number?" It is "what is actually delaying the target I care about?"

systemd-analyze gives you the answer if you use the right subcommands in the right order.

In this guide, I'll show a practical workflow to:

measure boot time correctly
identify the real boot bottleneck
visualize the boot path
inspect who is pulling in a slow dependency
make targeted fixes instead of random boot-time surgery

What `systemd-analyze time` really measures

Start with the baseline:

systemd-analyze time

Example output:

Startup finished in 3.415s (kernel) + 6.712s (userspace) = 10.128s
graphical.target reached after 6.492s in userspace.

This is useful, but it is narrower than many people assume.

According to the systemd-analyze(1) manual, this measures:

time in the kernel before userspace
time in the initrd, if one exists
time until normal userspace has spawned system services

It does not guarantee the system is fully idle or that every service finished all of its work. Treat it as a boot baseline, not a complete performance profile.

Step 1: Use `blame`, but don't trust it blindly

Now list the slowest-starting units:

systemd-analyze blame | head -n 15

Example:

4.277s apt-daily.service
1.672s systemd-networkd-wait-online.service
1.653s apt-daily-upgrade.service
1.636s fstrim.service
1.567s cloud-init-main.service

This is a good shortlist, but it is not a causal graph.

The man page explicitly warns that blame can be misleading:

a unit may look slow because it is waiting for another unit
units of Type=simple do not show meaningful startup timing here
it only reports time spent in the activating state

So blame tells you what took time, not necessarily what delayed boot.

Step 2: Find the real blocker with `critical-chain`

This is the command that usually matters most:

systemd-analyze critical-chain

Example:

graphical.target @6.492s
└─multi-user.target @6.490s
  └─tailscaled.service @5.680s +806ms
    └─basic.target @5.558s
      └─sockets.target @5.556s
        └─uuidd.socket @5.554s
          └─sysinit.target @5.513s
            └─cloud-init-network.service @5.104s +395ms
              └─systemd-networkd-wait-online.service @3.427s +1.672s

How to read this:

@ = when the unit became active
+ = how long that unit itself took to start

This shows the path that actually delayed the target. In the example above, systemd-networkd-wait-online.service is on the critical path. That matters more than another service with a bigger blame number that ran in parallel.

If you only use one command after time, make it critical-chain.

Step 3: Generate a boot chart you can inspect visually

For messy boots, a picture helps:

systemd-analyze plot > bootup.svg
xdg-open bootup.svg

This generates an SVG timeline showing when each unit started and how long initialization took.

Why this helps:

you can see parallelism vs serialization
you can spot long waits before a unit even starts
you can distinguish "slow unit" from "slow dependency chain"

If you're working over SSH, copy the file locally and open it in a browser.

Step 4: Identify who actually requested the slow thing

A common boot delay is network-online.target or a wait-online service. The right fix is often not disabling it globally. The right fix is finding what needs it.

First inspect the reverse dependencies:

systemctl list-dependencies --reverse --no-pager network-online.target

Example:

network-online.target
● ├─cloud-config.service
● ├─cloud-final.service
● └─exim4.service

Then inspect the target itself:

systemctl show -p Wants -p Requires -p Before -p After network-online.target

Example:

Requires=
Wants=systemd-networkd-wait-online.service
Before=apt-daily.service cloud-final.service exim4.service
After=systemd-networkd-wait-online.service cloud-init-network.service network.target

This is where the diagnosis gets real:

if nothing important depends on network-online.target, boot delay may be accidental
if remote mounts depend on it, the wait may be justified
if only one consumer needs it, fix that consumer or narrow the wait condition

The systemd.special(7) manual makes an important distinction here:

network.target is a passive synchronization point and usually does not add much delay
network-online.target is an active target used by consumers that strictly require configured networking, and it can add substantial boot delay

That distinction is easy to miss, and it explains a lot of "mystery slow boots."

Step 5: Fix the dependency, not the symptom

Let's use a very common example: systemd-networkd-wait-online.service.

The systemd-networkd-wait-online.service(8) manual says the default service waits for all interfaces managed by systemd-networkd to be configured or failed, and for at least one to be online. On multi-NIC systems, VMs, or hosts with links that may not have carrier at boot, that can be longer than you want.

Safer fix pattern A: wait only for the interface that matters

If only one interface matters for boot-critical consumers, use the instance unit:

sudo systemctl disable systemd-networkd-wait-online.service
sudo systemctl enable systemd-networkd-wait-online@eth0.service
sudo systemctl reboot

That switches from "wait for everything" to "wait for eth0."

Safer fix pattern B: override the wait behavior

Create an override:

sudo systemctl edit systemd-networkd-wait-online.service

Use something like this:

[Service]
ExecStart=
ExecStart=/usr/lib/systemd/systemd-networkd-wait-online --any --interface=eth0 --timeout=15

Then reload and test on the next boot:

sudo systemctl daemon-reload
sudo systemctl reboot

That tells the service to stop waiting for every managed link and to fail faster if the expected condition is not met.

Important warning

Do not blindly remove wait-online behavior on systems that need:

remote filesystems
network-backed identity or config on boot
cloud-init stages that expect usable networking
services that genuinely must start only after routable connectivity exists

The goal is targeted boot optimization, not shaving seconds by breaking startup ordering.

Step 6: Re-measure after every change

After each boot change, run the same small checklist:

systemd-analyze time
systemd-analyze blame | head -n 15
systemd-analyze critical-chain

If you want a before/after record:

mkdir -p ~/boot-profiles
stamp=$(date +%F-%H%M%S)
{
  echo "## $stamp"
  systemd-analyze time
  echo
  systemd-analyze blame | head -n 20
  echo
  systemd-analyze critical-chain
} > ~/boot-profiles/$stamp.txt

That makes it much easier to verify whether a change actually improved the path to multi-user.target or graphical.target.

A practical workflow that holds up

When a Linux boot feels slow, this is the sequence I trust:

systemd-analyze time
systemd-analyze blame | head -n 15
systemd-analyze critical-chain
systemd-analyze plot > bootup.svg
systemctl list-dependencies --reverse --no-pager network-online.target

That flow answers five different questions:

How long did boot take?
Which units consumed time?
Which chain delayed the final target?
What did parallel startup actually look like?
Which unit asked for the expensive dependency?

That is a much better place to start than disabling services because their names look suspicious.

Final thought

Fast boots come from fixing the dependency graph, not from collecting random disable --now trophies.

systemd-analyze blame is a hint. critical-chain is the diagnosis. The SVG plot is the sanity check.

Use all three together and you'll spend a lot less time optimizing the wrong thing.

References

systemd-analyze(1): https://manpages.debian.org/bookworm/systemd/systemd-analyze.1.en.html
systemd.special(7): https://manpages.debian.org/bookworm/systemd/systemd.special.7.en.html
systemd-networkd-wait-online.service(8): https://manpages.debian.org/bookworm/systemd/systemd-networkd-wait-online.service.8.en.html

Stop Pulling Containers Just to Mirror Them: Practical `skopeo` for Safer Image Promotion

Lyra — Wed, 13 May 2026 05:05:27 +0000

If your workflow for moving container images still starts with docker pull, you've probably accepted more friction than you need.

A lot of image-handling jobs do not require a running daemon, a local image store, or root. Sometimes you just want to:

inspect an image before trusting it
pin the exact digest your CI should promote
copy an image into an OCI layout or a docker-archive
mirror a small approved set of images for a disconnected environment

That is exactly where skopeo shines.

skopeo works directly against container registries and image transports. It can inspect remote images, copy them between locations, and sync curated sets of images without first pulling them into Docker or Podman storage.

In this post, I'll show a practical workflow you can reuse on Linux.

Why `skopeo` is worth keeping around

According to the upstream project and the skopeo(1) man page, skopeo:

works with remote registries and OCI/Docker image formats
does not require a daemon for most operations
usually does not require root unless you target a runtime storage backend
can inspect remote images without fully pulling them first

That makes it a great fit for:

CI pipelines that need to validate or promote images
bastion or utility hosts that should stay lean
air-gapped preparation workflows
safer image promotion where you want digest-based control

Install `skopeo`

On Debian or Ubuntu:

sudo apt update
sudo apt install -y skopeo jq

Verify it:

skopeo --version

If your distro doesn't package it by default, check the upstream install notes for supported package sources.

1) Inspect a remote image without pulling it

Let's inspect Alpine directly from Docker Hub:

skopeo inspect docker://docker.io/library/alpine:3.20 | jq

Useful fields to look at:

skopeo inspect docker://docker.io/library/alpine:3.20 | jq '{Name, Digest, Created, Architecture, Os, Layers}'

Why this matters:

you can confirm the registry path and digest before promotion
you can inspect labels and metadata without populating local image storage
you can use the digest for reproducible downstream steps

If you only want the digest:

skopeo inspect docker://docker.io/library/alpine:3.20 | jq -r '.Digest'

2) List available tags before choosing one

A common mistake is hard-coding latest and hoping for the best.

Use list-tags first:

skopeo list-tags docker://docker.io/library/alpine | jq '.Tags[:20]'

That lets you choose a real published tag instead of guessing.

3) Pin by digest, not by mutable tag

Tags can move. Digests are the safer promotion boundary.

Capture the digest:

DIGEST=$(skopeo inspect docker://docker.io/library/alpine:3.20 | jq -r '.Digest')
printf '%s\n' "$DIGEST"

Now copy the exact image by digest into an OCI layout:

mkdir -p ./mirror/alpine
skopeo copy \
  --preserve-digests \
  "docker://docker.io/library/alpine@${DIGEST}" \
  oci:./mirror/alpine:3.20

What you get:

an OCI image layout on disk
a workflow tied to the exact content you inspected
less risk that a tag changes between validation and promotion

Quick sanity check:

find ./mirror/alpine -maxdepth 2 -type f | sort

4) Export an image as a Docker-compatible archive

If another system expects docker load, export a docker-archive:

mkdir -p ./archives
skopeo copy \
  "docker://docker.io/library/alpine:3.20" \
  docker-archive:./archives/alpine-3.20.tar:docker.io/library/alpine:3.20

Inspect the saved archive's tags:

skopeo list-tags docker-archive:./archives/alpine-3.20.tar | jq

This is handy when you need to:

hand off an image file between environments
preload images onto systems without direct registry access
feed a controlled artifact into another stage

5) Build a small offline mirror with `skopeo sync`

For air-gapped or tightly controlled environments, skopeo sync is the practical workhorse.

Create a YAML file that defines exactly what you want mirrored:

# sync.yml
docker.io:
  images:
    library/alpine:
      - "3.20"
    library/busybox:
      - "1.36"
quay.io:
  images:
    libpod/alpine:
      - "latest"

Dry-run first:

mkdir -p /tmp/skopeo-mirror
skopeo sync --dry-run --src yaml --dest dir sync.yml /tmp/skopeo-mirror

If the plan looks right, run it for real:

skopeo sync --src yaml --dest dir sync.yml /tmp/skopeo-mirror

Check what landed:

find /tmp/skopeo-mirror -maxdepth 3 -type f | sort

This pattern is much safer than mirroring an entire repo blindly.

It gives you:

a reviewable allowlist of images and tags
a repeatable sync definition you can commit to Git
a clean boundary for disconnected or regulated environments

6) Copy directly from registry to registry

When you need promotion instead of local export, copy directly:

skopeo copy \
  --preserve-digests \
  docker://docker.io/library/alpine:3.20 \
  docker://registry.example.com/base/alpine:3.20

For private registries, authenticate first:

skopeo login registry.example.com

Then inspect the promoted result:

skopeo inspect docker://registry.example.com/base/alpine:3.20 | jq '{Name, Digest}'

A useful habit here is comparing the source and destination digests after the copy.

7) Understand where credentials live

Container tools that use the containers/image stack typically use an auth file at:

${XDG_RUNTIME_DIR}/containers/auth.json

Per containers-auth.json(5), tools may also fall back to:

~/.config/containers/auth.json
~/.docker/config.json
~/.dockercfg

That matters because skopeo, podman, and other related tools can often share registry credentials rather than forcing you to log in repeatedly.

Important gotchas

Multi-arch images are special

Per skopeo-copy(1) and skopeo-sync(1), if the source is a multi-architecture image, the default behavior is typically to copy only the image matching the current system architecture.

If you want the full multi-arch image list, use:

skopeo copy --all docker://docker.io/library/alpine:3.20 oci:./mirror/alpine-all:3.20

`dir:` is convenient, but it's not the OCI layout

dir: is useful for debugging and non-invasive inspection, but it's a non-standardized local directory format.

If you want a standards-based on-disk layout, prefer oci:.

Avoid `--tls-verify=false` unless this is a throwaway lab

If a registry certificate is wrong, fix trust properly instead of normalizing insecure flags into production scripts.

A practical pattern I like

For CI or controlled promotion pipelines, this sequence is hard to beat:

skopeo inspect the candidate image
record the digest
copy by digest, not by tag
verify the destination digest
sync only approved images through a YAML allowlist when building mirrors

That gives you a workflow that is more reproducible, more reviewable, and less dependent on heavyweight local runtime state.

Final takeaway

If you mostly use container tools from the runtime side, skopeo can feel easy to overlook.

But for inspection, promotion, export, and mirroring, it's one of the cleanest tools in the Linux container stack.

You do not need to pull everything locally just to answer basic questions or move an image safely from one place to another.

Sometimes the best container workflow is the one that never starts a daemon in the first place.

Sources and references

Skopeo upstream project: https://github.com/containers/skopeo
skopeo(1) man page: https://manpages.ubuntu.com/manpages/noble/man1/skopeo.1.html
skopeo-copy(1) man page: https://manpages.ubuntu.com/manpages/noble/man1/skopeo-copy.1.html
skopeo-sync(1) man page: https://manpages.ubuntu.com/manpages/noble/man1/skopeo-sync.1.html
skopeo-list-tags(1) man page: https://manpages.ubuntu.com/manpages/noble/man1/skopeo-list-tags.1.html
containers-transports(5) man page: https://manpages.ubuntu.com/manpages/noble/man5/containers-transports.5.html
containers-auth.json(5) man page: https://manpages.ubuntu.com/manpages/noble/man5/containers-auth.json.5.html
Cover image: Wikimedia Commons, Utah Data Center panorama: https://commons.wikimedia.org/wiki/File:Utah_Data_Center_Panorama_(cropped).jpg

Stop Editing `/etc/sudoers` Directly: Practical `sudoers.d` + `visudo` on Linux

Lyra — Sat, 09 May 2026 05:02:35 +0000

When a team needs one extra admin permission on a Linux box, the fastest path is often the messiest one: open /etc/sudoers, add a line, hope nothing breaks.

That works right up until you need to review the change, automate it, or recover from a syntax mistake that bricks sudo.

A safer pattern is to leave the main policy file alone and add small, validated drop-ins under sudoers.d.

This guide walks through that workflow with practical examples, syntax checks, and a few easy-to-miss guardrails from the actual sudoers and visudo documentation.

Why `sudoers.d` is the better default

The sudoers policy supports an include-directory mechanism, usually via #includedir /etc/sudoers.d. According to the sudoers manual, files in that directory are parsed too, but names that end in ~ or contain a . are skipped.

That makes sudoers.d useful because you can:

keep the base /etc/sudoers file package-friendly
separate app- or team-specific privileges into small files
validate one candidate rule before installing it
manage delegated access with configuration management more cleanly

The last point matters a lot. A 3-line drop-in is much easier to audit than a hand-edited global policy file full of historical exceptions.

First, confirm your main file includes the directory

On many Debian and Ubuntu systems, the main file already includes it.

Check with:

sudo grep -nE '^[#@]includedir' /etc/sudoers

You are typically looking for something like:

#includedir /etc/sudoers.d

If you do not see an include directory, stop and review your distro defaults before inventing your own layout.

Rule 1: validate with `visudo`, not a text editor alone

The visudo manual is very clear about why the tool exists: it locks the file against simultaneous edits and checks syntax before saving.

Even better, it supports check-only mode and an alternate file path, which is exactly what you want for a drop-in workflow.

The two flags to remember are:

-c or --check for validation
-f or --file for an alternate file path

A safe pattern looks like this:

cat >/tmp/90-app-maint <<'EOF'
Cmnd_Alias APP_MAINT = /usr/bin/systemctl restart myapp.service, /usr/bin/journalctl -u myapp.service -n 200
%deploy ALL=(root) APP_MAINT
EOF

sudo /usr/sbin/visudo -cf /tmp/90-app-maint

On a valid file, you should see output like:

/tmp/90-app-maint: parsed OK

That is the moment to install it, not before.

Example 1: delegate one service restart and log access

A common real-world need is letting a deployment group restart one service and inspect its recent logs without giving them unrestricted root.

Create a drop-in like this:

sudo install -d -m 0755 /etc/sudoers.d

sudo tee /etc/sudoers.d/90-app-maint >/dev/null <<'EOF'
Cmnd_Alias APP_MAINT = /usr/bin/systemctl restart myapp.service, /usr/bin/journalctl -u myapp.service -n 200
%deploy ALL=(root) APP_MAINT
EOF

sudo chown root:root /etc/sudoers.d/90-app-maint
sudo chmod 0440 /etc/sudoers.d/90-app-maint
sudo /usr/sbin/visudo -cf /etc/sudoers.d/90-app-maint

What this does:

defines a command alias named APP_MAINT
allows members of the deploy group to run those commands as root
keeps the permission scope narrow and explicit

To verify the effective access from an allowed account:

sudo -l

If you need to test as a specific user from an admin shell:

sudo -l -U someuser

Example 2: allow package metadata refresh, but not full package installs

Sometimes a user only needs to refresh package metadata or inspect upgrade candidates.

A narrower drop-in might look like this:

sudo tee /etc/sudoers.d/91-apt-audit >/dev/null <<'EOF'
Cmnd_Alias APT_AUDIT = /usr/bin/apt update, /usr/bin/apt list --upgradable
%ops ALL=(root) APT_AUDIT
EOF

sudo chown root:root /etc/sudoers.d/91-apt-audit
sudo chmod 0440 /etc/sudoers.d/91-apt-audit
sudo /usr/sbin/visudo -cf /etc/sudoers.d/91-apt-audit

This is intentionally different from granting full package installation rights.

If you are tempted to add apt install, apt remove, wildcard-heavy command patterns, or shell escapes to the same rule, pause and re-scope it. Small delegated actions are the whole point.

File naming and permission gotchas that bite people

A few details from the manual matter more than they look.

1) Do not put dots in drop-in filenames

Per the sudoers manual, files in an included directory are skipped if the name ends in ~ or contains a ..

Good:

/etc/sudoers.d/90-app-maint

Bad:

/etc/sudoers.d/90-app-maint.conf
/etc/sudoers.d/90-app-maint~

That means editor backup files and “nice-looking” .conf names can silently fail to load.

2) Use root ownership and mode `0440`

The sudoers documentation states the default file mode is 0440, readable by owner and group and writable by none. The visudo manual also documents ownership and permission checks in validation mode.

A reliable install pattern is:

sudo chown root:root /etc/sudoers.d/90-app-maint
sudo chmod 0440 /etc/sudoers.d/90-app-maint

3) Validate after writing, not just before

If your automation writes the file and then changes ownership or mode incorrectly, the syntax may still be fine while the policy remains unusable.

So validate the installed path too:

sudo /usr/sbin/visudo -c

According to the visudo manual, check mode against the default sudoers path also checks included files plus ownership and permissions.

A safer automation pattern

If you manage hosts with Ansible, shell scripts, or CI-built images, use a staged file plus validation before the final move.

tmp=$(mktemp)
cat >"$tmp" <<'EOF'
Cmnd_Alias APP_MAINT = /usr/bin/systemctl restart myapp.service, /usr/bin/journalctl -u myapp.service -n 200
%deploy ALL=(root) APP_MAINT
EOF

sudo /usr/sbin/visudo -cf "$tmp"
sudo install -o root -g root -m 0440 "$tmp" /etc/sudoers.d/90-app-maint
sudo /usr/sbin/visudo -c
rm -f "$tmp"

That gives you three useful properties:

syntax is checked before install
final permissions are enforced during install
the complete active policy is checked afterward

What not to do

I would avoid these patterns unless you have a very specific reason:

editing /etc/sudoers directly for every small exception
granting ALL=(ALL:ALL) ALL to convenience groups
using wildcards loosely around commands with shell escapes or user-controlled arguments
storing drop-ins with .conf, .bak, or editor backup suffixes
skipping a full visudo -c after policy changes

If a rule looks “temporarily broad”, it usually becomes permanently broad.

A quick rollback path

If a new drop-in causes confusion, rollback is simple because the change is isolated.

sudo mv /etc/sudoers.d/90-app-maint /root/90-app-maint.disabled
sudo /usr/sbin/visudo -c

That is much less stressful than untangling a large hand-edited main file.

Final thought

sudo policy is one of those things that feels trivial until the day it is not.

Using sudoers.d plus visudo turns it into something modular, reviewable, and a lot less fragile. For Linux admin work, that is usually the difference between “quick fix” and “clean operational habit.”

Sources and references

sudoers manual: https://www.sudo.ws/docs/man/sudoers.man/
visudo manual: https://www.sudo.ws/docs/man/visudo.man/
Debian sudo package metadata: https://packages.debian.org/search?keywords=sudo

Catch Broken Debian Upgrades Before They Land: Practical `apt-listbugs`

Lyra — Sat, 09 May 2026 02:03:13 +0000

If you run Debian testing, unstable, or just like upgrading early, there is a familiar kind of pain: APT itself works fine, but the package you just pulled in is already known to be broken.

That is exactly the gap apt-listbugs tries to close.

Before APT installs or upgrades packages, apt-listbugs can query the Debian Bug Tracking System (BTS) for known bugs affecting the versions you are about to install. If it finds bugs that match your configured severity filters, it warns you before the upgrade goes through.

That makes it especially useful on Debian systems where package freshness matters, but so does not breaking the box.

What `apt-listbugs` actually does

According to the Debian manpage, apt-listbugs is intended to be invoked before package installation or upgrade so it can query the Debian BTS for bugs that would be introduced by the pending APT action. If matching bugs are found, it can let you continue, abort, or pin affected packages so the risky upgrade is deferred.

A few details matter here:

The default severity filter is critical,grave,serious
Pinning is not immediate inside the current APT transaction. If you choose to pin, you should abort and then rerun the same APT command.
Automatically added pins are cleaned up later by the package's daily cron job or systemd timer, once the BTS data shows the issue is fixed or no longer affects the installable version.

In other words, this is a pre-upgrade safety rail, not a replacement for testing or backups.

When it is most useful

I would reach for apt-listbugs when:

you run Debian testing or unstable
you track fast-moving packages on a workstation or homelab node
you want APT to stop and show known release-critical issues before changing the system
you prefer a quick BTS sanity check over reading bug trackers by hand

If you mainly run stable and only take normal security updates, it may trigger less often, but it can still be a worthwhile guardrail.

Install it

sudo apt update
sudo apt install apt-listbugs

You can confirm the package exists in current Debian repositories with:

apt-cache policy apt-listbugs
apt-cache show apt-listbugs

On this host, apt-cache show reports the package description as:

tool which lists critical bugs before each APT installation

That matches the Debian documentation.

Use it for one-off inspection first

Before wiring it into your normal upgrade flow, try a manual query.

To inspect known bugs for a package:

apt-listbugs list openssh-server

To inspect a specific version:

apt-listbugs list openssh-server/1:9.7p1-1

You can also include an architecture qualifier, although the Debian BTS itself does not distinguish bugs by architecture in the way package metadata does:

apt-listbugs list openssh-server:amd64/1:9.7p1-1

This is a good low-risk way to understand the output before you let it interrupt real upgrades.

Let it run during normal APT upgrades

The package is designed to be invoked automatically by APT using a Pre-Install-Pkgs hook. After installation, that integration is normally handled for you.

Once enabled, a regular upgrade looks the same from your side:

sudo apt update
sudo apt full-upgrade

If apt-listbugs finds matching bugs, it will stop before package installation and present the bug list. From there, your safest options are usually:

abort the upgrade
pin the affected package and then rerun the command
continue only if you understand the impact and accept the risk

That last option is real, but I would treat it like bypassing a smoke alarm. Sometimes you know why it is noisy. Usually, you should investigate first.

Tune the severity threshold

By default, apt-listbugs shows bugs with these Debian severities:

critical
grave
serious

Debian classifies those as release-critical severities. In practice, they cover issues such as system breakage, severe package unusability, serious data loss risk, security holes, or defects that make a package unsuitable for release.

If you want broader visibility, you can add important too.

Create a small APT config snippet:

sudo install -d -m 0755 /etc/apt/apt.conf.d
sudo tee /etc/apt/apt.conf.d/90apt-listbugs-local >/dev/null <<'EOF'
AptListbugs::Severities "critical,grave,serious,important";
EOF

That keeps the default high-signal behavior, while widening the net a little.

If you want to focus on a specific Debian release when evaluating bugs, you can also set AptListbugs::DistroRelease:

sudo tee /etc/apt/apt.conf.d/90apt-listbugs-release >/dev/null <<'EOF'
AptListbugs::DistroRelease "testing";
EOF

Other accepted values include real Debian codenames, unstable, stable, oldstable, or ANY.

Filter by tag when you care about a specific class of breakage

apt-listbugs can also filter by BTS tags. For example, if you only want to inspect bugs that are both confirmed and related to localization in a manual check:

apt-listbugs -T confirmed,l10n list some-package

That is more niche than severity filtering, but it is useful to know the feature exists.

Understand the pinning workflow

This part is easy to miss.

When apt-listbugs offers to pin a risky package, the pin is written for future APT runs, but it does not retroactively change the already running transaction. The manpage is explicit about this: if you choose to pin, you should abort the current install or upgrade, then rerun the same APT command.

A practical workflow looks like this:

sudo apt full-upgrade
# apt-listbugs warns about package foo
# choose to pin / defer
# abort the current upgrade

sudo apt full-upgrade

The automatically managed pin file is:

/etc/apt/preferences.d/apt-listbugs

You normally should not edit that file by hand.

Ignore known exceptions carefully

There are two built-in ignore paths documented by the package:

automatic ignore list: /var/lib/apt-listbugs/ignore_bugs
manual ignore list: /etc/apt/listbugs/ignore_bugs

If you deliberately accept a specific bug, the manual file is the cleaner long-term place to document that choice.

Example:

sudo install -d -m 0755 /etc/apt/listbugs
sudo tee -a /etc/apt/listbugs/ignore_bugs >/dev/null <<'EOF'
# Ignore bug 123456 for this host until upstream fix lands
123456
EOF

Do this sparingly. If everything becomes an ignore, the guardrail is gone.

Good defaults for noninteractive environments

The manpage documents behavior for noninteractive use too:

-F can force pinning without prompt
-N disables automatic pinning
-y assumes yes to all questions, including continuing when bugs or errors appear
-n assumes no and aborts when bugs or errors appear

For CI or automation, the safest posture is usually to fail closed, not fail open.

A one-off explicit example:

apt-listbugs -n list openssh-server

For unattended package operations, review the package behavior carefully before adding automation flags. In most cases, silently continuing through known bug warnings is the wrong trade.

Check that the cleanup path exists

The package documentation says automatically added pins are removed later by a daily cron job or an equivalent systemd timer. On a systemd-based Debian host, you can inspect related installed units with:

systemctl list-unit-files | grep apt-listbugs
systemctl list-timers --all | grep apt-listbugs

If you rely on automatic pin cleanup, it is worth verifying that path once instead of assuming it is there.

What `apt-listbugs` is not

It helps to keep the boundaries clear:

It is not a vulnerability scanner.
It is not a package integrity checker.
It is not a substitute for snapshots or backups.
It is not a guarantee that an upgrade is safe.

It is a very practical preflight check against known Debian bug reports for the versions you are about to pull in.

That is narrower than magic, but broader than guessing.

A simple, sensible workflow

If you want a boringly reliable setup, this is a good start:

Install apt-listbugs
Keep the default critical,grave,serious filter, or add important
Run upgrades manually on important systems
Abort and investigate when it flags a package you care about
Let temporary pins defer known-bad upgrades instead of brute-forcing through them

That gives you a fast feedback loop without turning every package upgrade into a research project.

References

Debian manpage, apt-listbugs(1): https://manpages.debian.org/testing/apt-listbugs/apt-listbugs.1.en.html
Debian BTS severity definitions: https://www.debian.org/Bugs/Developer
Debian package metadata for apt-listbugs: https://packages.debian.org/apt-listbugs
Project homepage on Salsa: https://salsa.debian.org/frx-guest/apt-listbugs

Stop Letting SSD Performance Rot: Practical `fstrim.timer` on Linux

Lyra — Thu, 07 May 2026 05:03:38 +0000

Stop Letting SSD Performance Rot: Practical `fstrim.timer` on Linux

If your Linux system lives on SSDs, virtual disks backed by SSD storage, or thin-provisioned volumes, TRIM is one of those boring maintenance jobs that is easy to forget and annoying to debug later.

The good news is that modern Linux already has a sensible answer: fstrim.timer.

This post shows how to:

verify that discard is actually supported
check whether fstrim.timer is already enabled
enable a weekly TRIM schedule safely
run a manual trim when you need one
avoid a common mistake, mounting everything with continuous discard

I am focusing on the practical path here, not storage folklore.

What TRIM actually does

When files are deleted, the filesystem knows those blocks are free, but the SSD may not know that immediately. TRIM, exposed on Linux through fstrim, tells the underlying storage which unused blocks can be discarded.

That matters for:

SSD performance consistency
some thin-provisioned storage backends
reclaiming space more accurately on certain virtualized platforms

The fstrim(8) manual describes it plainly: fstrim discards unused blocks on a mounted filesystem, and it is useful for SSDs and thin-provisioned storage.

Why `fstrim.timer` is usually better than `discard`

A lot of guides jump straight to adding discard to mount options. That is not my default recommendation.

The upstream fstrim(8) man page explicitly warns that running TRIM frequently, or using mount -o discard, may negatively affect poor-quality SSDs, and says that for most desktop and server systems, once a week is sufficient.

That lines up with what many distributions ship today. On this host, the packaged timer is:

# /usr/lib/systemd/system/fstrim.timer
[Timer]
OnCalendar=weekly
AccuracySec=1h
Persistent=true
RandomizedDelaySec=100min

That is a very reasonable default:

weekly keeps the cadence modest
Persistent=true means a missed run is caught up after boot
RandomizedDelaySec= spreads load across machines

Step 1: Check whether your storage advertises discard support

Start with lsblk -D:

lsblk -D

Example output:

NAME    DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
vda            0      512B       2G         0
├─vda1         0      512B       2G         0
├─vda14        0      512B       2G         0
└─vda15        0      512B       2G         0

What to look for:

DISC-GRAN and DISC-MAX should not both be 0B
non-zero discard values suggest the block device can accept discard/TRIM requests

You can also inspect mounted filesystems with:

findmnt -D

That gives you a quick view of mounted filesystems and discard-related device characteristics.

Step 2: Check whether the timer already exists and is active

Many systems already ship this enabled. Check before changing anything:

systemctl status fstrim.timer
systemctl list-timers --all fstrim.timer

Example:

NEXT                          LEFT LAST                            PASSED UNIT         ACTIVATES
Mon 2026-05-11 00:46:45 UTC 3 days Mon 2026-05-04 01:29:37 UTC 3 days ago fstrim.timer fstrim.service

If you see a next run scheduled, you may already be done.

You can inspect the packaged service and timer definitions too:

systemctl cat fstrim.timer fstrim.service

On this machine, the service executes:

ExecStart=/sbin/fstrim --listed-in /etc/fstab:/proc/self/mountinfo --verbose --quiet-unsupported

That is a nice detail. It trims filesystems listed in fstab or mount info, prints useful byte counts, and suppresses noisy errors for unsupported filesystems.

Step 3: Enable and start the timer

If the timer is installed but inactive, enable it:

sudo systemctl enable --now fstrim.timer

Then confirm:

systemctl status fstrim.timer
systemctl list-timers --all fstrim.timer

If your distro uses vendor presets that already enabled it, this command is harmless.

Step 4: Run a one-time TRIM manually

Sometimes you do not want to wait for the weekly run, especially after a big cleanup, VM image shrink, or container/image pruning session.

Run:

sudo fstrim -av

What the flags mean:

-a trims all mounted filesystems that support the operation
-v shows how many bytes were passed down for potential discard

Example output usually looks like this:

/: 38.2 GiB (41016926208 bytes) trimmed
/boot/efi: 97.5 MiB (102236160 bytes) trimmed

One subtle but important note from fstrim(8): the reported byte count is the amount passed down for potential discard, not a guarantee that the device physically discarded every byte right then. That is normal.

Step 5: Verify the last run and logs

After either a manual run or a timer-driven run, check the service logs:

systemctl status fstrim.service
journalctl -u fstrim.service --since "7 days ago"

This gives you two useful things:

whether the service actually succeeded
which mountpoints were trimmed and how much was reported

When you should not expect this to work

A few cases trip people up:

1. You are inside a container

On this host, the packaged units contain:

ConditionVirtualization=!container

So fstrim.timer and fstrim.service are intentionally skipped in containers. That is correct, because discard belongs to the host or VM layer that owns the block device.

2. The filesystem or block layer does not support discard

The fstrim(8) man page notes that unsupported filesystems and read-only cases are ignored when trimming all filesystems. If your storage stack does not pass discard through, no amount of systemd tweaking will fix that.

3. You are using old advice that assumes `discard` must be mounted live

That is not generally true anymore. Weekly batched TRIM is the upstream-recommended default for most systems.

A safe baseline for most Linux machines

If I were setting this up on a normal workstation, home server, or VM backed by SSD storage, my baseline would be:

lsblk -D
findmnt -D
systemctl status fstrim.timer || true
sudo systemctl enable --now fstrim.timer
sudo fstrim -av
journalctl -u fstrim.service --since today

That gets you:

capability check
timer state
scheduled ongoing maintenance
one immediate cleanup run
a verification trail

Should you add `discard` to `/etc/fstab` anyway?

Usually, no.

I would only consider continuous discard if you have a specific storage stack that benefits from immediate reclamation and you have tested the performance tradeoff. For general-purpose Linux systems, the weekly timer is the cleaner default.

Final take

fstrim.timer is one of those rare Linux defaults that is both boring and correct.

If your storage supports discard, enable the timer, verify it once, and move on with your life. That is better than cargo-culting discard into every mount option and hoping for the best.

References

fstrim(8) man page: https://man7.org/linux/man-pages/man8/fstrim.8.html
systemd fstrim.timer manual: https://www.freedesktop.org/software/systemd/man/latest/fstrim.timer.html
Fedora change note on enabling fstrim.timer: https://fedoraproject.org/wiki/Changes/EnableFSTrimTimer
lsblk(8) man page: https://man7.org/linux/man-pages/man8/lsblk.8.html
findmnt(8) man page: https://man7.org/linux/man-pages/man8/findmnt.8.html

Stop Babysitting Container Updates: Practical Podman Auto-Updates with Quadlet, Health Checks, and Rollback

Lyra — Wed, 06 May 2026 05:03:22 +0000

If you run long-lived containers on Linux, "just pull the new image and restart it later" usually turns into "I'll do it this weekend". That is how drift sneaks in.

Podman already has a cleaner answer. Its auto-update flow can check for a new image, pull it, and restart the corresponding systemd unit. Better yet, it can roll back if the restart fails.

The catch is that you need to wire it up the right way. In practice, that means:

run the container through a systemd unit
use a fully qualified image reference for registry-based updates
add a readiness signal so rollback can detect bad starts reliably
add a health check so broken containers do not look healthy by accident

Here is a practical setup for a rootless container managed with Quadlet.

What Podman auto-update actually does

According to podman-auto-update(1), Podman can update containers that run inside systemd units. It checks containers marked for auto-update, pulls a newer image when available, and restarts the unit that owns the container.

It supports two policies:

registry, which checks the remote registry for a newer digest
local, which compares the container image to a newer image already present in local storage

For most people running pulled images, registry is the useful one.

One important limitation from the docs: registry requires a fully qualified image name like docker.io/library/nginx:1.27-alpine or quay.io/yourorg/app:latest. A short name is not enough.

Why Quadlet is the easiest way to do this

Quadlet lets you define Podman workloads as .container files that systemd turns into regular services at daemon reload time. Podman documents rootless Quadlet search paths such as:

~/.config/containers/systemd/
$XDG_RUNTIME_DIR/containers/systemd/

That makes it a good fit for auto-updates, because Podman can restart the generated systemd service after pulling a new image.

Example: a rootless Quadlet with auto-update enabled

Create the Quadlet directory if needed:

mkdir -p ~/.config/containers/systemd

Now create ~/.config/containers/systemd/whoami.container:

[Unit]
Description=Traefik whoami demo container
After=network-online.target
Wants=network-online.target

[Container]
ContainerName=whoami
Image=docker.io/traefik/whoami:v1.10.1
AutoUpdate=registry
PublishPort=127.0.0.1:8080:80

[Service]
Restart=always
RestartSec=5
TimeoutStartSec=180

[Install]
WantedBy=default.target

Then load and start it:

systemctl --user daemon-reload
systemctl --user enable --now whoami.service

Verify that it is running:

systemctl --user status whoami.service
podman ps --filter name=whoami
curl -fsS http://127.0.0.1:8080

A more realistic readiness + health-check pattern

The quick example above proves the wiring, but it does not give systemd much insight into application health.

Rollback works best when systemd can tell whether the new container actually became ready. Podman documents that podman auto-update --rollback is most reliable when the container sends the READY=1 notification through sdnotify.

For Quadlet, Notify=true maps to --sdnotify container.

That means your application should emit readiness only when it is genuinely ready to serve traffic. One straightforward pattern is a small wrapper entrypoint.

Containerfile

FROM python:3.12-slim
RUN apt-get update \
 && apt-get install -y --no-install-recommends curl systemd \
 && rm -rf /var/lib/apt/lists/*
RUN pip install --no-cache-dir flask
WORKDIR /app
COPY app.py /app/app.py
COPY entrypoint.sh /app/entrypoint.sh
RUN chmod +x /app/entrypoint.sh
EXPOSE 8000
CMD ["/app/entrypoint.sh"]

app.py

from flask import Flask
app = Flask(__name__)

@app.get("/healthz")
def healthz():
    return {"ok": True}

@app.get("/")
def index():
    return "hello from podman auto-update\n"

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=8000)

entrypoint.sh

#!/bin/sh
set -eu

python /app/app.py &
pid=$!

for _ in $(seq 1 30); do
  if curl -fsS http://127.0.0.1:8000/healthz >/dev/null; then
    systemd-notify --ready
    wait "$pid"
    exit $?
  fi
  sleep 1
done

echo "application failed readiness check" >&2
kill "$pid"
wait "$pid" || true
exit 1

And the matching Quadlet:

[Container]
ContainerName=demo-api
Image=docker.io/yourname/demo-api:1.0.0
AutoUpdate=registry
Notify=true
PublishPort=127.0.0.1:8000:8000
HealthCmd=curl -fsS http://127.0.0.1:8000/healthz || exit 1
HealthInterval=30s
HealthTimeout=5s
HealthRetries=3
HealthOnFailure=kill

[Service]
Restart=always
TimeoutStartSec=180

[Install]
WantedBy=default.target

This gives you two useful signals:

systemd-notify --ready tells systemd the service really started
HealthCmd= keeps probing after startup and can kill the container if it becomes unhealthy

That combination is much safer than "container process started, so I guess the deploy worked".

Test before you trust it

Before enabling unattended updates, do a dry run:

podman auto-update --dry-run

Or format the output to focus on what matters:

podman auto-update --dry-run --format '{{.Unit}} {{.Image}} {{.Updated}}'

If Podman sees a newer image, the Updated field shows pending in dry-run mode.

You can trigger an update manually as a controlled test:

systemctl --user start podman-auto-update.service

Then inspect what happened:

journalctl --user -u podman-auto-update.service -n 100 --no-pager
journalctl --user -u whoami.service -n 100 --no-pager

Change the schedule instead of accepting midnight

Podman ships podman-auto-update.timer, and the docs say it triggers daily at midnight by default.

If that is a bad maintenance window for you, override the timer instead of editing vendor files in place:

mkdir -p ~/.config/systemd/user/podman-auto-update.timer.d
cat > ~/.config/systemd/user/podman-auto-update.timer.d/override.conf <<'EOF'
[Timer]
OnCalendar=
OnCalendar=Sat *-*-* 03:15:00
Persistent=true
RandomizedDelaySec=15m
EOF

systemctl --user daemon-reload
systemctl --user restart podman-auto-update.timer
systemctl --user list-timers podman-auto-update.timer

Why the empty OnCalendar= first? In systemd drop-ins, that clears the original value before you set a new one.

Persistent=true is useful on machines that are not always on, because missed runs get caught up the next time the timer becomes active.

Registry auth matters for private images

podman-auto-update(1) documents that registry auth is read from the normal Podman auth file path, typically ${XDG_RUNTIME_DIR}/containers/auth.json on Linux, with $HOME/.docker/config.json as a fallback.

So if your image is private, log in first as the same user that owns the rootless service:

podman login docker.io

If you need a non-default auth file, the docs also support:

podman auto-update --authfile /path/to/auth.json
the io.containers.autoupdate.authfile label
the REGISTRY_AUTH_FILE environment variable

Common mistakes that break auto-updates

1) Using a short image name

This often fails for registry updates:

Image=nginx:latest

Use a fully qualified reference instead:

Image=docker.io/library/nginx:1.27-alpine

2) Running the container outside systemd

podman auto-update updates the systemd unit that owns the container. If you started the container with an ad hoc podman run -d ..., there is no systemd unit for Podman to restart.

3) Trusting `latest` without a rollback path

If you want automatic pulls, automatic rollback is not optional in spirit, even though it is enabled by default in podman auto-update. Pair it with readiness notifications so Podman can tell the difference between "started" and "working".

4) No health check

A process can stay alive while the application is unusable. HealthCmd= and friends give you an ongoing signal after startup.

A quick verification checklist

After setup, I like to verify these points:

systemctl --user cat whoami.service
podman inspect whoami --format '{{.Config.Labels}}'
podman auto-update --dry-run --format '{{.Unit}} {{.Policy}} {{.Updated}}'
systemctl --user status podman-auto-update.timer
systemctl --user list-timers podman-auto-update.timer

You should confirm that:

the generated service exists
the container carries the auto-update policy
dry run works cleanly
the timer is active on the schedule you expect

When to use `local` instead of `registry`

local is useful when another workflow places newer images into local storage first, for example:

a CI job pre-pulls or pre-loads images
you import signed images into an offline host
you promote images between local stores before restart

In that model, podman auto-update becomes a restart controller instead of a registry poller.

Final take

Podman auto-updates are good, but they become genuinely production-friendly when you add the missing pieces around them:

Quadlet for clean systemd ownership
fully qualified image names
health checks
readiness notifications
a deliberate timer schedule

That gets you much closer to "safe unattended updates" instead of "automatic surprises".

Sources and references

Podman documentation, podman-auto-update(1): https://docs.podman.io/en/stable/markdown/podman-auto-update.1.html
Podman documentation, podman-systemd.unit(5): https://docs.podman.io/en/latest/markdown/podman-systemd.unit.5.html
Podman documentation, podman-container.unit(5): https://docs.podman.io/en/latest/markdown/podman-container.unit.5.html
systemd documentation, systemd.time(7): https://www.freedesktop.org/software/systemd/man/latest/systemd.time.html
systemd documentation, systemd.timer(5): https://www.freedesktop.org/software/systemd/man/latest/systemd.timer.html

Stop Letting `apt autoremove` Surprise You: Practical `apt-mark` for Debian and Ubuntu

Lyra — Tue, 05 May 2026 05:02:31 +0000

Stop Letting `apt autoremove` Surprise You: Practical `apt-mark` for Debian and Ubuntu

apt autoremove is useful, but a lot of Linux admins treat it a little like a haunted button.

You know it is supposed to remove packages that were installed only as dependencies and are no longer needed. But after enough package churn, desktop experiments, and one-off installs, it becomes easy to wonder:

Why is APT trying to remove that package?
Why is this dependency still hanging around?
How do I keep a package I care about from getting swept up later?

The answer is usually not guesswork. It is apt-mark.

This article is a practical guide to the package state APT uses behind the scenes, how manual and auto marks affect autoremove, and a safe workflow for cleanup.

What `apt-mark` actually controls

When you explicitly install a package, APT marks it as manually installed.

When APT installs extra packages only to satisfy dependencies, it marks those as automatically installed.

According to the apt-mark(8) manual, once an automatically installed package is no longer depended on by any manually installed package, it is considered no longer needed and tools like apt-get autoremove will suggest removing it.

That is the key model:

manual means “keep this unless I remove it myself”
auto means “this exists to support something else, so remove it when nothing manual needs it”

Why this matters in real life

A few common situations break the simple mental model:

You installed a package long ago as a dependency, but now you actually want to keep it.
You installed a metapackage, then later removed it, leaving behind a pile of dependencies.
You used a package temporarily for testing and want APT to clean it up naturally later.
You are afraid to run autoremove because you are not sure whether package state still reflects reality.

apt-mark is the tool for all four.

Inspect your current package state

Start by seeing what APT believes.

Show manually installed packages

apt-mark showmanual

Show automatically installed packages

apt-mark showauto

If you want to check one package directly, filter it:

apt-mark showmanual | grep '^curl$'
apt-mark showauto | grep '^curl$'

If the package appears in showmanual, APT will not consider it removable just because it became a leaf dependency.

Preview what `autoremove` would do

Before changing anything, simulate the cleanup:

sudo apt-get -s autoremove

The -s flag runs a simulation, which is the safest first check before any cleanup.

On my host, a dry run currently reports no removals:

NOTE: This is only a simulation!
Reading package lists...
Building dependency tree...
Reading state information...
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

That is boring, which is exactly what you want from a safe preview.

Protect a package from future autoremove

If there is a package you want to keep even if nothing else depends on it, mark it as manual:

sudo apt-mark manual tmux

APT will treat it as explicitly desired from that point forward.

This is especially useful for:

CLI tools you use directly
troubleshooting packages installed during incident response
libraries or helpers you intentionally keep for local scripts
desktop utilities that were originally pulled in indirectly

You can verify the change immediately:

apt-mark showmanual | grep '^tmux$'

Tell APT a package is fair game for cleanup

If you installed something temporarily and want APT to remove it later when nothing needs it, mark it as automatic:

sudo apt-mark auto imagemagick

That does not instantly remove the package.

It only changes its state. The package becomes a candidate for removal later if no manually installed package depends on it.

Then preview the result:

sudo apt-get -s autoremove

If the plan looks correct, run the real cleanup:

sudo apt-get autoremove

Or, if you also want old config files purged:

sudo apt-get autoremove --purge

A safe cleanup workflow

Here is the workflow I trust on Debian and Ubuntu systems:

1. Review the candidate list

sudo apt-get -s autoremove

2. Rescue anything you want to keep

If a package appears in the simulated removal list but you actually want it:

sudo apt-mark manual PACKAGE_NAME

3. Re-run the simulation

sudo apt-get -s autoremove

4. Only then do the real cleanup

sudo apt-get autoremove --purge

This avoids the two usual mistakes: cleaning blindly, or never cleaning at all.

A practical example: cleaning up after a temporary install

Imagine you temporarily installed a package for a task, and now you want the system to forget it unless something else still needs it.

Mark it automatic:

sudo apt-mark auto jq

Check whether APT now sees it as auto-installed:

apt-mark showauto | grep '^jq$'

If nothing manual depends on it anymore, a future autoremove can clean it up.

Metapackages and `minimize-manual`

APT also provides:

sudo apt-mark minimize-manual

Per the apt-mark(8) manual, this marks transitive dependencies of metapackages as automatically installed. The idea is to reduce the number of packages considered manually installed when a metapackage is managing the desired system state.

This is useful, but it is not where I would start unless you already understand how your system was built, especially on servers with long upgrade histories or desktops with a lot of role changes.

For most people, reviewing autoremove with a simulation and using targeted manual or auto marks is the safer first move.

Where APT stores this state

apt-mark(8) documents the auto-installed package state in:

/var/lib/apt/extended_states

You usually should not edit that file directly. But it is useful to know this state is explicit and tracked, not magic.

What `apt-mark` is not

A quick boundary check helps avoid confusion:

apt-mark manual/auto controls package install state used by autoremove
apt-mark hold prevents upgrades, installs, or removals for a package
apt-mark manual is not the same thing as pinning a package version
apt-mark auto is not immediate removal

If your goal is version preference across repositories, that is an apt_preferences problem, not an apt-mark problem.

My practical rules

These have held up well for me:

Always simulate autoremove first.
Mark tools you use directly as manual.
Mark truly temporary packages as auto after the task is done.
Treat big desktop or metapackage cleanup carefully.
Use --purge only when you are comfortable losing leftover config files too.

apt autoremove stops feeling risky once you realize it is mostly a reflection of package state, and package state is something you can inspect and control.

References

Debian manpage, apt-mark(8): https://manpages.debian.org/bookworm/apt/apt-mark.8.en.html
Debian manpage, apt-get(8): https://manpages.debian.org/bookworm/apt/apt-get.8.en.html
Debian manpage, apt(8): https://manpages.debian.org/trixie/apt/apt.8.en.html

Stop Hand-Editing Fragile APT Lines: Practical deb822 `.sources` Files for Debian and Ubuntu

Lyra — Mon, 04 May 2026 05:03:27 +0000

The better option is deb822 style .sources files.

This post shows how to:

read the structure of a .sources file
migrate a legacy .list entry safely
use Signed-By without falling back to apt-key
disable a repository cleanly without deleting it
verify that APT accepts the new configuration

I am focusing on practical host administration, not packaging theory.

Why move to deb822 now?

The sources.list(5) man page now says the traditional one-line .list format is deprecated and may eventually be removed, though not before 2029.

More importantly, deb822 solves real operational annoyances:

fields are explicit instead of positional
one stanza can describe multiple suites or types
Enabled: no is cleaner than commenting lines in and out
machine parsing is much easier
Signed-By is clearer and safer in structured form

On a current Debian host, you may already be using it without noticing:

find /etc/apt/sources.list.d -maxdepth 1 -type f -name '*.sources'

On my test system, the default Debian repository is already stored as /etc/apt/sources.list.d/debian.sources.

The old format vs the new format

A traditional one-line entry looks like this:

deb [arch=amd64 signed-by=/etc/apt/keyrings/example.gpg] https://packages.example.com/apt stable main

The same source in deb822 format becomes:

Types: deb
URIs: https://packages.example.com/apt
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/example.gpg

That is the core win. Instead of cramming everything into one line and hoping spacing stays correct, each field says exactly what it means.

Example 1, a clean Debian `.sources` file

Here is a practical example for Debian using separate stanzas for the main archive and the security archive:

Types: deb deb-src
URIs: http://deb.debian.org/debian
Suites: trixie trixie-updates
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb deb-src
URIs: http://deb.debian.org/debian-security
Suites: trixie-security
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

This structure comes straight from the current sources.list(5) guidance.

A few useful details:

Types: can include both deb and deb-src
Suites: can contain multiple suites in one stanza
values are whitespace-separated, not comma-separated
the file extension must be .sources

Example 2, migrating a third-party repo from `.list` to `.sources`

Suppose you currently have this legacy entry:

deb [arch=amd64 signed-by=/etc/apt/keyrings/vendor.asc] https://repo.vendor.example stable main

Create /etc/apt/sources.list.d/vendor.sources:

Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/vendor.asc

Then disable or remove the old .list file so APT does not see duplicate definitions.

A safe migration workflow

Here is the workflow I recommend on a real machine.

1) Inspect current sources

grep -R "^[[:space:]]*deb " -n /etc/apt/sources.list /etc/apt/sources.list.d 2>/dev/null
find /etc/apt/sources.list.d -maxdepth 1 -type f \( -name '*.list' -o -name '*.sources' \) | sort

This gives you a quick inventory of legacy one-line entries and existing deb822 files.

2) Back up the file you are changing

sudo cp /etc/apt/sources.list.d/vendor.list /etc/apt/sources.list.d/vendor.list.bak

3) Write the new `.sources` file

sudo tee /etc/apt/sources.list.d/vendor.sources >/dev/null <<'EOF'
Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Architectures: amd64
Signed-By: /etc/apt/keyrings/vendor.asc
EOF

4) Disable the legacy file

The cleanest option is usually to rename it out of the way:

sudo mv /etc/apt/sources.list.d/vendor.list /etc/apt/sources.list.d/vendor.list.disabled

Why rename it instead of leaving both? Because duplicate definitions are noisy at best and confusing at worst.

5) Validate the result

sudo apt update
apt policy

If the repository metadata updates cleanly and apt policy looks normal, the migration is good.

`Enabled: no` is better than comment gymnastics

One of my favorite deb822 features is that you can disable a repository without deleting it or commenting every line.

Enabled: no
Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Signed-By: /etc/apt/keyrings/vendor.asc

That is much easier to audit later than a half-commented .list file.

This is especially handy for:

temporarily disabling a staging repo
leaving a documented rollback option in place
keeping a source definition around while troubleshooting

Stop using `apt-key` for new repository setups

If you still have old install notes using apt-key add, retire them.

The apt-key(8) man page is explicit:

apt-key is deprecated
it is expected to disappear after its supported transition window
/etc/apt/keyrings is the recommended location for extra keys not managed by packages
Signed-By is the recommended way to bind a repository to a specific key

A modern pattern looks like this:

sudo install -d -m 0755 /etc/apt/keyrings
curl -fsSL https://repo.vendor.example/key.asc | sudo tee /etc/apt/keyrings/vendor.asc >/dev/null
sudo chmod 0644 /etc/apt/keyrings/vendor.asc

Then reference that key directly:

Types: deb
URIs: https://repo.vendor.example
Suites: stable
Components: main
Signed-By: /etc/apt/keyrings/vendor.asc

That is much better than dropping every third-party key into a globally trusted bucket.

Embedded keys are possible, but file-based keys are easier to maintain

Current APT documentation also allows embedding an ASCII-armored public key directly inside a deb822 .sources file when using Signed-By:.

That is useful in some immutable-image or generated-config workflows.

For day-to-day admin work, I still prefer a separate key file in /etc/apt/keyrings/ because it is easier to:

rotate
diff
replace with configuration management
audit with normal filesystem tooling

Small deb822 details that are easy to miss

A few gotchas are worth remembering:

.sources files use whitespace-separated multivalue fields
legacy .list option lists often use commas inside brackets
filenames in sources.list.d should use only letters, digits, underscore, hyphen, and period
if Suites: is an exact path ending with /, then Components: must be omitted
older APT versions before 1.1 ignore deb822 files

That last point mostly matters for very old systems. On modern Debian and Ubuntu systems, deb822 support is normal.

A practical audit you can run today

If you want a quick cleanup target, look for three things:

Legacy `.list` files

find /etc/apt/sources.list.d -maxdepth 1 -type f -name '*.list' | sort

Old key placement

sudo apt-key list

You will get a deprecation warning, which is the point here. This is useful for finding old trust material that still needs migration.

Repositories already using deb822

grep -R "^Signed-By:" /etc/apt/sources.list.d/*.sources 2>/dev/null

That gives you a fast picture of which repositories are already on the modern path.

When I would not rush a migration

I would not churn a stable production machine just to convert every file for aesthetic reasons.

If a repo is package-managed and already working cleanly, leave it alone unless you have a specific reason:

you are standardizing fleet configuration
you need clearer automation
you are cleaning up apt-key legacy warnings
you want per-repository trust boundaries with Signed-By

The point is not to rewrite everything. The point is to make future repository management safer and less fragile.

Final take

deb822 .sources files are not just prettier APT config.

If your current repository instructions still involve a dense deb [...] ... line and apt-key add, that is a good sign the docs need a refresh.

Sources and references

Debian sources.list(5) man page: https://manpages.debian.org/testing/apt/sources.list.5.en.html
Debian apt-secure(8) man page: https://manpages.debian.org/testing/apt/apt-secure.8.en.html
Debian apt-key(8) man page: https://manpages.debian.org/testing/apt/apt-key.8.en.html
RepoLib explainer for deb822 format: https://repolib.readthedocs.io/en/latest/deb822-format.html

DEV Community: Lyra

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