The apt-get
command is one of the primary package management tools on Debian-based Linux distributions. Mastering apt-get update
vs apt-get upgrade
is critical for maintaining systems up-to-date and secure. This extensive 2600+ word guide will cover everything from the technical internals behind these operations to best practices for hardening your systems using apt.
Understanding APT – The Advanced Package Tool
Before diving into apt-get
specifically, it helps to understand what Advanced Package Tool (APT) is and how Debian-based Linux systems manage software.
APT simplified:
- High-level package management framework for Debian, Ubuntu and related distributions
- Consists of multiple command line tools like
apt-get
and graphical interfaces - Automates tasks like installing, upgrading, configuring, and removing packages
- Relies on
dpkg
low-level package manager for core functionality
Some key ways APT enhances the underlying dpkg
tool:
- Fetches packages automatically from configured repositories
- Resolves package dependencies when installing
- Provides signature validation for security
- Offers command line and visual interfaces
Under the hood, APT handles a few key areas of package management:
Package Repositories
APT relies on designated internet servers to host downloadable .deb
packages, typically organized by Debian/Ubuntu release. The main configuration file /etc/apt/sources.list
specifies repository locations to sync package metadata and downloads from.
Local Package Cache
APT tools all utilize /var/cache/apt/archives/
as a local store of downloaded .deb package files to avoid re-downloading, with periodic cleaning. Package indexes and metadata get cached locally under /var/lib/apt/lists
.
Metadata Storage
Information about packages like versions, dependencies, descriptions get stored in the APT database at /var/lib/apt
. This metadata index gets updated by apt-get update
and consulted when installing/upgrading packages to determine eligibility.
Now that we‘ve covered how APT manages Debian/Ubuntu packages overall, we can better understand the specific roles of apt-get update
and apt-get upgrade
.
Apt-Get Update In Depth
The apt-get update
command serves the specific purpose of refreshing the local APT package metadata index with latest information from all configured repositories in /etc/apt/sources.list
and /etc/apt/sources.list.d
.
sudo apt-get update
Let‘s explore what exactly happens during an update:
-
APT contacts all designated repositories checking for new signed Release files – these list available packages for the repo.
-
New Packages and Sources index files containing package metadata get downloaded – these list specific versions, dependencies etc.
-
Package hash summaries (Contents files) get updated locally.
-
All index data gets cached locally under
/var/lib/apt/lists
with old index data cleared out. -
The consolidated package list is analyzed against currently installed packages to determine new updates available for upgrade.
Note that apt-get update
only refreshes textual metadata indexes to reflect the latest upstream package state – no actual software packages get installed during this update process.
Visually, you can conceptualize the flow like this:
Apt update flowchart by author
The update output looks like this – fetching updated metadata from several repositories:
Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease
Get:3 http://archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:4 http://security.ubuntu.com/ubuntu focal-security/universe amd64 Packages [905 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]
...
Fetched 2558 kB in 5s (633 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
42 packages can be updated. Run ‘apt list --upgradable‘ to see them.
As we can see, all repository metadata gets updated in the background while the system processes which currently installed packages have available upgrades – but still nothing installed yet!
When Should You apt-get Update?
Here are the most common use cases for running apt-get update
:
- Before upgrading packages: Ensures latest package versions visible
- After editing
/etc/apt/sources.list
: Needed to refresh with new sources - When changing Debian/Ubuntu release channels (
stable
,testing
etc) to pickup different package manifests - Setting up new Debian/Ubuntu server: Initial sync to prime for installs
- Troubleshooting package errors: May fix inconsistencies like missing packages
As a general rule of thumb, its good practice to update the APT package indexes from repositories before any installs or upgrades via:
sudo apt-get update
This primes the system to avoid situations like installing outdated version of packages that newer versions exist upstream for already.
I recommend configuring a daily cron job to auto-run apt-get update
in the background as well for low maintenance index refreshing:
/etc/cron.daily/apt-update
#!/bin/sh
/usr/bin/apt-get update
This ensures your system stays on top of new versions without frequent manual intervention. Don‘t worry, updates themselves are very low overhead by just updating metadata indices.
Understanding Apt-Get Upgrade
While apt-get update
fetches the metadata required for upgrades, the apt-get upgrade
command actually installs updated package versions based on that refreshed metadata:
sudo apt-get upgrade
What apt-get upgrade
does:
- Consults the latest APT package indexes from
apt-get update
- Analyzes currently installed packages that have newer versions available
- Calculates complete upgrade plan based on versioned dependencies between packages
- Downloads required newer
.deb
archives from configured repositories - Calls
dpkg
to unpack and install each new.deb
package - Repeats for all packages with updates available
So in summary, apt-get upgrade
serves as the workhorse for actually downloading real software updates and installing them onto the operating system – powered by metadata from apt-get update
.
A sample upgrade session looks like:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following NEW packages will be installed:
linux-headers-5.4.0-121 linux-headers-5.4.0-121-generic
linux-image-5.4.0-121-generic
The following packages will be upgraded:
linux-headers-generic linux-image-generic
6 upgraded, 2 newly installed, 0 to remove and 36 not upgraded.
Need to get 48.6 MB of archives.
After this operation, 348 MB of additional disk space will be used.
...
Here we see configuration details like packages upgraded, newly installed, additional space required all output before downloading and unpacking operations occur.
When Should You apt-get Upgrade?
It‘s important to remember upgrades should only be executed after first running apt-get update
. This ensures the system knows about all eligible upgrades available.
Beyond that, it‘s good practice to periodically upgrade installed packages rather than just on an as-needed basis when problems arise. Some guidelines around scheduling upgrades:
- Daily or weekly quick upgrades for things like security patches on servers
- Before major apt operations like global
dist-upgrade
- On workstations, upgrade regularly based on user preference for latest software
Finding the right balance avoids both excessive upgrades when unneeded and risk of outdated packages.
Key Differences Between apt-get update vs upgrade
While it‘s easy to mix up apt-get update
and apt-get upgrade
based on their similar names, remembering their distinct purposes goes a long way:
Apt-Get Update | Apt-Get Upgrade |
---|---|
Fetches package metadata/indices | Installs actual package upgrades |
Updates local package index | Requires updated package lists from update |
Non-intrusive metadata sync | Can modify installed software behavior |
Fast incremental updates | May take time downloading/unpacking packages |
The mnemonic I use is refresh knowledge, then apply knowledge. First update
to refresh package indices, then upgrade
to leverage that refreshed metadata to upgrade actual packages.
Always update
first before upgrade
!
Common Usage Combinations
Here are some common examples of using apt-get update
and apt-get upgrade
together for managing packages:
Update indexes then upgrade packages
sudo apt-get update
sudo apt-get upgrade
Update, upgrade, clean caches, then install new package
sudo apt-get update
sudo apt-get upgrade
sudo apt-get clean
sudo apt-get install nginx
Update indexes and distribution upgrade together
sudo apt-get update && sudo apt-get dist-upgrade
The &&
operator chains the update and dist-upgrade together while ensuring update runs first.
Upgrade an individual package without full upgrade
sudo apt-get update
sudo apt-get install python3
Targeted single package installs/upgrades can be done without upgrading everything.
Address failed package installs
sudo apt-get update
sudo apt --fix-broken install
Updates indexes then attempts to fix broken dependencies.
Best Practices and Analysis
Now that we‘ve covered the basics of using apt-get update
and apt-get upgrade
for package management, let‘s explore some best practices surrounding upgrades and updates from an expert perspective.
Frequency of Updates and Upgrades
Finding the right cadence between updating packaging indexes from repositories and actually upgrading installed packages boils down to balancing system stability with staying up-to-date.
For servers, I typically recommend:
- Nightly indexing updates:
apt-get update
daily via cron - Weekly upgrades: Download patches, upgrades available each week
The nightly update allows gradual downloading of new metadata without risk of unexpected major changes. Then regular weekly upgrades apply those incremental changes.
For desktop systems, users tend to prefer latest software so can optionally upgrade more aggressively as new versions release.
Automating Updates and Upgrades
While ad-hoc manual commands work, creating crontab schedules for regular apt-get update
and apt-get upgrade
execution ensures consistency, reduces admin overhead, and minimizes security risk.
A sample auto-update crontab schedule:
/etc/cron.daily/apt
#!/bin/sh
# Refresh repos nightly at 12AM
0 0 * * * apt-get update
30 0 * * 0 apt-get upgrade # Weekly upgrades
This ensures nightly updates to prepare plus weekly batches of upgrade installs.
For even more control, look at dedicated APT tools like Unattended Upgrades.
Potential Issues When Neglecting Updates
Failing to regularly apt-get update
package indexes and apt-get upgrade
software leaves systems exposed on multiple fronts:
Security vulnerabilities: Unpatched CVEs get exploited
Buggy software: Stability/reliability regressions missed
Missing features: Can‘t leverage new versions without upgrading
Errors when installing packages: Indexes outdated
I‘ve seen neglected Debian servers with four year uptime and extremely outdated packages that experience all the above issues. Don‘t let that happen!
While upgrading does introduce some change management overhead, it pays off tremendously in security and stability.
Diagnosing and Fixing Common Apt Problems
While APT handles dependencies automatically, it‘s not entirely foolproof – packages can still get broken especially when mixing repositories like third party PPAs. Some common failure scenarios:
Could not resolve dependencies
Unable to correct problems, you have held broken packages.
Fix by updating indices then using apt --fix-broken
to rebuild dependency tree.
GPG key errors
NO_PUBKEY A14703C3F756E6E7
Indicates missing repository signing key. Fetch key from keyserver and re-update.
404 Not Found errors
Repositories have moved or been retired – adjust sources list.
Outdated index issues
Failed to fetch http://old-ubuntu.com/ubuntu/dists/focal/InRelease
Repository no longer active – replace sources. Retry installs after updating indices.
Carefully reading error output provides clues on how best to resolve. Don‘t hesitate to retry installs after updating indexes with apt-get update
as a first troubleshooting step.
Apt vs Aptitude vs Apt-Get
While apt-get
remains the most popular tool for package management from the command line in 2023, Debian and Ubuntu systems also come with two other primary interfaces – apt
and aptitude
.
Here is a comparison between the major APT tools:
Tool | Can Update Indices | Can Upgrade Packages | Additional Capabilities |
---|---|---|---|
apt-get | Yes | Yes | Mature, well-tested CLI |
apt | Yes | Yes | Enhanced CLI, progress bars |
aptitude | Yes | Yes | Ncurses GUI, visualization |
The apt-get
command provides the underlying core functionality and stability. apt
builds on it with a more modern CLI experience like multi-arch support, colorized output, and progress reporting.
And aptitude
layers an ncurses graphical package manager on top of CLI apt with visual interfaces for update management and task automation.
So while all three leverage the same APT libraries, they each provide slightly different interfaces or enhancements around the underlying functionality.
For servers, apt-get
tends to still be the most universal and compatible interface. But apt
brings better user experience for human administrators. Either is a safe option.
Security Hardening for APT Repositories
Since APT pulls package updates directly from designated repositories, some good security practices around properly curating, maintaining, and validating those sources are:
- Comment out deb-src entries if unused to reduce attach surface
- Validate GPG release signing keys with packet maintainers
- Monitor for emergency repo redirects indicating compromises
- Limit less audited third party PPAs when possible
- Periodically review sources list for stale/unneeded repos
- Ensure local APT caches like
/var/cache/apt
have restricted permissions to protect against tampering
Proactively managing repository configurations defends against supply chain attacks through compromised packages or indices.
Conclusions and Summary
We‘ve covered a tremendous amount of ground around effectively utilizing APT apt-get update
and apt-get upgrade
for managing packages – from key technical details to security best practices.
To recap the key points:
apt-get update
- Refreshes package metadata indices from repositories
- Important before upgrading packages or installing new ones
- Lightweight, downloads only index data for checking
- Run at least daily either manually or via cron
apt-get upgrade
- Actually upgrades installed packages based on refreshed metadata
- Does not install completely new packages
- Downloads and installs newer
.deb
archives - Ideally run at least weekly after updates
Core Differences
Apt-Get Update | Apt-Get Upgrade |
---|---|
Updates package liste | Performs actual upgrades |
Prepares system for upgrades | Relies on updated indices |
Fast metadata syncs | Intensive disk and cpu |
Common Combinations
sudo apt update && sudo apt upgrade
(update then upgrade)sudo apt update && sudo apt install nginx
(update before installing new package)
Best Practices
- Always update before upgrading
- Automate regular updates/upgrades via crontab
- Upgrade packages before major apt operations
- Address errors promptly and retry installs
Productive package management boils down to regularly refreshing metadata with apt-get update
and selectively applying upgrades using apt-get upgrade
to balance stability and currency. This guide should give you deep knowledge on using these pivotal apt-get
tools effectively.
Let me know if you have any other best practices around apt-get
!