CentOS Stream 10 Minimal on AWS User Guide

Overview

This guide covers launching and verifying the CentOS Stream 10 Minimal AMI from cloudimg on Amazon EC2. It is one version of the cloudimg CentOS Stream listing on AWS Marketplace; you pick it as the software version when you subscribe and launch. Every release and variant in the listing is described at /guides/centos-stream-aws/.

CentOS Stream 10 is the free, community-built enterprise Linux distribution maintained by the CentOS Project. It is developed just ahead of Red Hat Enterprise Linux 10: it carries the fixes and features of the next RHEL 10 minor release before RHEL ships them, as a continuous stream of updates rather than numbered point releases. This image starts from the official CentOS Stream 10 image for EC2 and adds four things:

• A trimmed package set. Packages a cloud server does not need are removed (the linux-firmware collection for physical hardware and the tuned tuning daemon on this build). Each removal is simulated first and refused if it would take a package the instance needs to boot, network or be reached. The list ships on the image. The Systems Manager agent is brought to its current release.
• CIS Level 1 Server remediation. The image is remediated with the OpenSCAP CIS Level 1 Server profile from SCAP Security Guide 0.1.82 (the CentOS Project's own signed scap-security-guide package and its CentOS Stream 10 content), then rebooted and evaluated. 284 of 286 scored rules pass (99.3%), the same on the build and on a freshly launched instance. Seven rules are waived because they cannot work on an EC2 image, each with its reason. The HTML report, the machine-readable results, the waiver list and a summary ship in /usr/share/doc/cloudimg/.
• EC2 defaults that keep you in control. Key-only SSH as ec2-user, root locked, no password on any account, SELinux enforcing, IMDSv2 required, a host firewall (firewalld) that allows SSH in and everything out, the current AWS Systems Manager agent, and time from the Amazon Time Sync Service.
• Fully patched at build time, with dnf-automatic applying all available updates on your instance every day. CentOS Stream publishes no separate security advisories, so there is no "security only" update set to choose; every update is applied.

What is on the image: CentOS Stream 10 (the 6.12 kernel), cloud-init, OpenSSH, firewalld, chrony, SELinux (targeted policy, enforcing), the AWS Systems Manager agent, auditd, rsyslog, AIDE file integrity checking, dnf-automatic, OpenSCAP and the pinned SCAP Security Guide content used for the evaluation.

Default user: ec2-user · Architecture: x86_64 · Boot mode: legacy BIOS · Root volume: 10 GiB gp3, XFS (grows to the size you choose at launch)

These images are remediated with an OpenSCAP profile and ship their own evaluation report. They are not CIS Hardened Images, and CIS has not reviewed or certified them. CIS publishes no benchmark for CentOS Stream; the profile is the Red Hat Enterprise Linux 10 CIS content as packaged by the CentOS Project for CentOS Stream 10.

Connecting to your instance

Version	SSH user	Root device
CentOS Stream 10 Minimal	ec2-user	/dev/sda1 (10 GiB gp3)

Security posture

• No known credential. There is no default password and no baked in SSH key. The only key that works is the EC2 key pair you choose at launch, which cloud-init installs for ec2-user on first boot.
• Key-only SSH. PasswordAuthentication no, PermitRootLogin no, keyboard-interactive off. The root account has no password and is locked. EC2 Instance Connect, which adds a second way to push SSH keys, is not installed.
• Per-instance identity. SSH host keys and the machine ID are generated fresh on every instance, so no two instances share a host key.
• IMDSv2 required. The AMI is registered with ImdsSupport v2.0, so instances launched from it refuse token-less (IMDSv1) metadata requests by default.
• SELinux enforcing with the targeted policy, as CentOS Stream ships it.
• Host firewall. firewalld's public zone allows only SSH and the DHCPv6 client inbound and allows all outbound traffic, so the SSM agent, metadata service, DNS, time and package updates keep working.
• Only SSH listens on the network. Nothing else on the image listens on any address.

Prerequisites

1. An AWS account and permission to launch EC2 instances
2. An EC2 key pair in the Region you launch in
3. A security group that allows TCP 22 from your own address (not from the whole internet)

Recommended instance type: m5.large. The image runs on any current x86_64 instance type. Like every CentOS Stream 10 build for x86_64, it needs a processor with the x86-64-v3 feature level (AVX2), which current-generation EC2 x86 instance types provide.

Step 1: Launch the instance

Option A: AWS Marketplace console

1. Open the cloudimg CentOS Stream listing on AWS Marketplace and choose View purchase options, then Subscribe. One subscription covers every version in the listing.
2. Once the subscription is active, choose Launch your software.
3. Choose One-click launch from AWS Marketplace (or Launch from EC2 Console for full control), then in Version choose CentOS Stream 10 Minimal - YYYY-MM-DD (the date is when the version was added) and your Region.
4. Instance type: m5.large is recommended; any current x86_64 type works. The software charge is $0.04 per vCPU per hour.
5. Key pair: choose your EC2 key pair. It is the only way in. RSA and ED25519 keys both work.
6. Security group: allow inbound TCP 22 from your own IP address or network only.
7. Storage: the root volume is 10 GiB gp3 by default. Choose a larger size if you need one; cloud-init grows the root partition and filesystem to fill it on first boot.
8. Metadata: leave the defaults. The image already requires IMDSv2. Then choose Launch.

Option B: AWS CLI

Run this on your own workstation. Replace the AMI ID with the one shown for your Region on the Marketplace launch page, and the key pair, security group and subnet with your own. The root device of this AMI is /dev/sda1:

aws ec2 run-instances \
  --image-id ami-0123456789abcdef0 \
  --instance-type m5.large \
  --key-name my-key-pair \
  --security-group-ids sg-0123456789abcdef0 \
  --subnet-id subnet-0123456789abcdef0 \
  --block-device-mappings 'DeviceName=/dev/sda1,Ebs={VolumeSize=20,VolumeType=gp3}' \
  --tag-specifications 'ResourceType=instance,Tags=[{Key=Name,Value=centos-stream-10-minimal}]'

You do not need --metadata-options: the AMI already makes IMDSv2 required.

Step 2: Connect via SSH

From your workstation, connect as ec2-user with the key pair you chose:

ssh -i ~/.ssh/my-key-pair.pem ec2-user@<public-ip>

There is no password to enter. If SSH asks for one, or says Too many authentication failures, see Troubleshooting below.

You can also connect without opening port 22 at all through AWS Systems Manager Session Manager, if the instance has an instance profile that allows Systems Manager. The agent is installed and running on this image.

Step 3: Confirm the release

cat /etc/centos-release
grep -E '^(NAME|VERSION|ID|VERSION_ID|PLATFORM_ID|PRETTY_NAME)=' /etc/os-release
uname -srm

Expected output:

CentOS Stream release 10 (Coughlan)
NAME="CentOS Stream"
VERSION="10 (Coughlan)"
ID="centos"
VERSION_ID="10"
PLATFORM_ID="platform:el10"
PRETTY_NAME="CentOS Stream 10 (Coughlan)"
Linux 6.12.0-277.el10.x86_64 x86_64

CentOS Stream has no point releases: the release is just 10, and the system moves forward through ordinary dnf updates. Your kernel version will be newer if updates have installed since this image was built.

Step 4: See what the Minimal trim removed

The image lists exactly what was removed, and anything that a removal would have taken with it is kept and listed instead:

cat /usr/share/doc/cloudimg/minimal-manifest.txt
rpm -qa | wc -l

Expected output:

Minimal version: packages 533 -> 531
Removed:
  linux-firmware
  tuned
Kept (a removal would have taken a protected package, or it failed):
545

The trim takes the package count from 533 to 531. Nothing had to be kept back. linux-firmware holds firmware for physical network, graphics and wireless hardware that an EC2 instance does not have; tuned is a power and performance tuning daemon. The base image is already small, so the rest of the candidate list (sound firmware, Cockpit, Plymouth, the sos report collector) was never installed. After the trim, the CIS remediation adds the tools it needs (OpenSCAP, AIDE, the journal upload client and their libraries), which is why a new instance has 545 packages. The count on your instance moves by a few as kernels and updates install.

Anything removed is one sudo dnf install away from the standard CentOS Stream repositories.

Step 5: Read the compliance evidence

The evaluation the build ran after its reboot ships on the image:

ls -lh /usr/share/doc/cloudimg/
python3 -c "import json; s=json.load(open('/usr/share/doc/cloudimg/cis-l1-summary.json')); print('profile:      ', s['profileLabel'], '(SCAP Security Guide', s['ssgVersion'] + ')'); print('scored rules: ', s['scored'], ' pass:', s['pass'], ' fail:', s['fail'], ' rate:', str(s['ratePct']) + '%'); print('waived:       ', s['waived'], ' not applicable:', s['notapplicable']); print('evaluated at: ', s['evaluatedAt'])"

Expected output:

total 32M
-rw-r--r--. 1 root root  29M Oct 20 03:10 cis-l1-arf.xml
-rw-r--r--. 1 root root 2.4M Oct 20 03:10 cis-l1-report.html
-rw-r--r--. 1 root root 1.3K Oct 20 03:10 cis-l1-summary.json
-rw-r--r--. 1 root root 1.8K Oct 20 03:10 cis-l1-tailoring.xml
-rw-r--r--. 1 root root 2.9K Oct 20 03:10 cis-l1-waivers.txt
-rw-r--r--. 1 root root  140 Oct 20 03:06 minimal-manifest.txt
-rw-r--r--. 1 root root 1.6K Oct 20 03:06 scap-security-guide-LICENSE.txt
profile:       CIS Level 1 Server (SCAP Security Guide 0.1.82)
scored rules:  286  pass: 284  fail: 2  rate: 99.3%
waived:        7  not applicable: 31
evaluated at:  2026-10-20T03:10:41Z

• cis-l1-report.html is the full OpenSCAP report, rule by rule. Copy it to your workstation and open it in a browser.
• cis-l1-arf.xml is the same evaluation in the machine-readable ARF format, for compliance tooling.
• cis-l1-tailoring.xml is the exact tailoring used, so you can re-run the same evaluation (Step 6).
• The pass rate is pass / (pass + fail + error + unknown). Rules that are not applicable to this machine, not selected, or waived are not counted.

To copy the report to your workstation, run this on the workstation:

scp -i ~/.ssh/my-key-pair.pem ec2-user@<public-ip>:/usr/share/doc/cloudimg/cis-l1-report.html .

The seven waived rules

grep -v '^#' /usr/share/doc/cloudimg/cis-l1-waivers.txt | cut -f1,2

Expected output:

partition_for_tmp   [single-volume-partitions]
grub2_password  [serial-console-and-boot]
ensure_root_password_configured [serial-console-and-boot]
accounts_maximum_age_login_defs [key-only-account-aging]
account_disable_post_pw_expiration  [key-only-account-aging]
sshd_limit_user_access  [ssh-access-list]
service_systemd-journal-upload_enabled  [log-remote-destination]

The full reason for each is the third column of the same file. In short:

• Separate /tmp partition: this version boots from one EBS root volume. (The LVM versions of this listing provide separate volumes for /tmp, /var, /var/log, /var/log/audit, /var/tmp and /home.)
• Boot loader and root passwords: a GRUB or root password would have to be baked into the image, giving every instance the same secret. Root stays locked with no password. Set your own if you need serial console access (see Step 11).
• Password ageing defaults: the accounts cloud-init creates are key-only. An ageing limit would expire them and lock the SSH key out. Accounts that do have a password are still aged.
• SSH AllowUsers/AllowGroups: a list fixed at build time would refuse accounts you create later. Your security group restricts who can reach port 22.
• Journal upload to a remote log server: the profile switches on systemd-journal-upload but sets no destination, and an image cannot know your log server. With no destination the service fails at every boot. systemd-journal-remote is installed and the upload service is left off: create /etc/systemd/journal-upload.conf with an [Upload] section and URL= for your collector (the packaged defaults are in /usr/lib/systemd/journal-upload.conf), then run sudo systemctl enable --now systemd-journal-upload.

The two rules that do not pass

python3 -c "import json; [print(r) for r in json.load(open('/usr/share/doc/cloudimg/cis-l1-summary.json'))['failingRules']]"

Expected output:

ensure_journald_and_rsyslog_not_active_together
ensure_redhat_gpgkey_installed

• journald and rsyslog together. The benchmark wants one logging system, not both. CentOS Stream runs journald and rsyslog together by default: journald keeps the structured system journal (persistent, in /var/log/journal), and rsyslog writes the traditional text logs (/var/log/messages, /var/log/secure, /var/log/cron) that many log shippers and audit procedures read. The image keeps both so neither kind of tooling loses its logs. If you standardise on one, for example the journal only, run sudo systemctl disable --now rsyslog on your instance and re-run Step 6.
• Red Hat's package signing key. The rule comes from the RHEL content and checks that Red Hat's own release key is in the RPM database. CentOS Stream packages are signed by the CentOS Project, not by Red Hat, so that key is neither shipped nor useful here. The CentOS Official Signing Key is installed, and every repository checks package signatures (gpgcheck=1); rpm -qa gpg-pubkey lists the keys. The image deliberately does not import a key that signs none of its packages.

Step 6: Re-run the evaluation yourself

You can repeat the evaluation at any time with the same content and tailoring. It takes under a minute:

sudo oscap xccdf eval \
  --tailoring-file /usr/share/doc/cloudimg/cis-l1-tailoring.xml \
  --profile xccdf_co.cloudimg_profile_cis-l1_ec2_single \
  --results /tmp/cis-check-results.xml --report /tmp/cis-check-report.html \
  /usr/share/xml/scap/ssg/content/ssg-cs10-ds.xml > /tmp/cis-check.log 2>&1
echo "oscap exit code: $? (2 = at least one rule did not pass)"
sudo python3 -c "import re,collections; c=collections.Counter(re.findall(r'<result>(\w+)</result>', open('/tmp/cis-check-results.xml').read())); s=sum(c[k] for k in ('pass','fail','error','unknown')); print(dict(sorted(c.items()))); print('pass rate: %.1f%%' % (100.0*c['pass']/s))"

Expected output:

oscap exit code: 2 (2 = at least one rule did not pass)
{'fail': 2, 'notapplicable': 31, 'notselected': 756, 'pass': 284}
pass rate: 99.3%

Your own report is at /tmp/cis-check-report.html. Use the ssg-cs10-ds.xml content shown above: the scap-security-guide package also ships ssg-rhel10-ds.xml, but that content only applies to Red Hat Enterprise Linux, so on CentOS Stream it reports almost every rule as not applicable. As you install software and change settings, re-run this to see how your changes affect the result.

Step 7: Confirm IMDSv2 is required

curl -s -o /dev/null -w 'IMDSv1 request without a token: HTTP %{http_code}\n' http://169.254.169.254/latest/meta-data/instance-id
TOKEN=$(curl -s -X PUT -H 'X-aws-ec2-metadata-token-ttl-seconds: 60' http://169.254.169.254/latest/api/token)
curl -s -H "X-aws-ec2-metadata-token: $TOKEN" -w '\n' http://169.254.169.254/latest/meta-data/placement/region

Expected output (your Region may differ):

IMDSv1 request without a token: HTTP 401
us-east-1

A request without a session token is refused with HTTP 401, and the same request with a token works. Scripts and SDKs on the instance must use IMDSv2; every current AWS SDK and the AWS CLI do this automatically.

Step 8: The host firewall and listening ports

sudo firewall-cmd --state
sudo firewall-cmd --list-all
sudo ss -tlnp

Expected output (the interface name and process IDs may differ):

running
public (default, active)
  target: default
  ingress-priority: 0
  egress-priority: 0
  icmp-block-inversion: no
  interfaces: ens5
  sources: 
  services: dhcpv6-client ssh
  ports: 
  protocols: 
  forward: yes
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules: 
State  Recv-Q Send-Q Local Address:Port Peer Address:PortProcess
LISTEN 0      128          0.0.0.0:22        0.0.0.0:*    users:(("sshd",pid=996,fd=7))
LISTEN 0      128             [::]:22           [::]:*    users:(("sshd",pid=996,fd=8))

• Only sshd listens, on port 22. Nothing else on the image opens a TCP port.
• The public zone allows ssh and dhcpv6-client (replies to the instance's IPv6 DHCP client, which is how an instance in an IPv6-enabled subnet gets its address). The CentOS default cockpit service is removed from the zone; Cockpit is not installed.
• The loopback interface sits in firewalld's trusted zone, with rules that drop traffic claiming a loopback source from anywhere else (a CIS requirement).

Opening a port for your own service takes two steps: allow it in the instance's security group, and allow it in firewalld. For example, for a web server on 443, run on the instance:

sudo firewall-cmd --permanent --add-service=https
sudo firewall-cmd --reload

If a port is open in the security group but not in firewalld (or the other way round), the traffic will not arrive.

Step 9: Time sync and the Systems Manager agent

systemctl is-active chronyd amazon-ssm-agent
chronyc -n sources

Expected output (the timings vary):

active
active
MS Name/IP address         Stratum Poll Reach LastRx Last sample               
===============================================================================
^* 169.254.169.123               3   4   377     1   -709ns[ +112us] +/-  546us

The ^* marks the source chrony is using: 169.254.169.123, the Amazon Time Sync Service. It is reachable from every instance without internet access, so time stays correct in a private subnet too.

The AWS Systems Manager agent is installed from Amazon's own package at its current release (3.3.5390.0 on this build). It is not in the CentOS Stream repositories, so dnf does not update it; Systems Manager can keep it current for you (the AWS-UpdateSSMAgent document, or the Auto update SSM Agent setting in Fleet Manager).

Step 10: Patch level and automatic updates

The image is fully patched at build time. Check what is pending now and how automatic updates are set up:

sudo dnf -q check-update --refresh
echo "dnf check-update exit code: $? (0 = nothing to update, 100 = updates available)"
grep -E '^(upgrade_type|apply_updates|reboot) =' /etc/dnf/automatic.conf
systemctl is-enabled dnf-automatic.timer
systemctl cat dnf-automatic.timer | grep -E '^(OnCalendar|RandomizedDelaySec)'
uname -r

Expected output on an instance launched soon after the image was built (later launches list the updates released since, with exit code 100):

dnf check-update exit code: 0 (0 = nothing to update, 100 = updates available)
upgrade_type = default
apply_updates = yes
reboot = never
enabled
OnCalendar=*-*-* 6:00
RandomizedDelaySec=60m
6.12.0-277.el10.x86_64

How dnf-automatic is configured on this image:

• upgrade_type = default installs every available update, not only security fixes. CentOS Stream's repositories carry no security advisory data, so a security-only setting would install nothing at all.
• apply_updates = yes installs the updates, not just downloads them.
• The timer runs daily at 06:00 (instance time, UTC by default) with a random delay of up to an hour.
• reboot = never: a new kernel or core library is installed but takes effect only after you reboot, at a time you choose.

Because CentOS Stream moves ahead of RHEL and updates arrive continuously, test updates on a non-production instance first if your workload is sensitive to package changes. To stop automatic updates, run sudo systemctl disable --now dnf-automatic.timer; to update everything now, run:

sudo dnf -y upgrade

Reboot if a new kernel was installed:

sudo systemctl reboot

Step 11: Security settings on the instance

getenforce
sudo passwd -S root
sudo sshd -T | grep -E '^(permitrootlogin|passwordauthentication|pubkeyauthentication|maxauthtries|clientaliveinterval|banner) '
cat /etc/issue.net

Expected output:

Enforcing
root L 2025-04-08 0 99999 7 -1
maxauthtries 4
clientaliveinterval 300
permitrootlogin no
pubkeyauthentication yes
passwordauthentication no
banner /etc/issue.net
Authorized users only. All activity may be monitored and reported.

• Enforcing means SELinux is on and enforcing the targeted policy. Keep it on; if your own software is denied, check sudo ausearch -m avc -ts recent rather than disabling SELinux.
• L in the second column means the root account is locked.
• maxauthtries 4 and clientaliveinterval 300 come from the CIS profile: SSH allows four authentication attempts per connection and checks idle sessions every five minutes.
• The banner text is shown before login.

EC2 Serial Console and recovery. No account on this image has a password, so the serial console cannot log in until you set one. If you want serial console access, set a password for your own user on your running instance (the password is yours and is not on the image):

sudo passwd ec2-user

Step 12: Disk layout, size, swap and file integrity

df -hT /
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT
sudo grep -E 'cc_growpart.*(resized|NOCHANGE)' /var/log/cloud-init.log | tail -1
swapon --noheadings --show | wc -l
sudo grep -h aide /etc/crontab

Expected output with the default 10 GiB root volume (on a larger volume, Size is larger and the cloud-init line says resized):

Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/nvme0n1p3 xfs   9.8G  2.1G  7.7G  22% /
NAME         SIZE TYPE FSTYPE MOUNTPOINT
nvme0n1       10G disk        
├─nvme0n1p1    1M part        
├─nvme0n1p2  200M part vfat   /boot/efi
└─nvme0n1p3  9.8G part xfs    /
2026-10-20 03:40:19,627 - cc_growpart.py[DEBUG]: '/' NOCHANGE: no change necessary (/dev/nvme0n1, 3)
0
05 4 * * * root /usr/sbin/aide --check

• Disk layout. This is the standard (not LVM) layout of the official CentOS Stream image: the root filesystem is XFS on partition 3 of the root volume, with /boot on the root filesystem. Partition 1 is the small BIOS boot partition the boot loader uses, and partition 2 is an EFI system partition the image carries but does not boot from (the AMI boots in legacy BIOS mode). If you need separate filesystems for /var, /var/log, /tmp or /home, or want to grow storage by adding volumes, choose the CentOS Stream 10 LVM version of this listing instead.
• Disk growth. cloud-init grows the root partition and filesystem to the volume size on first boot. To grow later, increase the EBS volume size in the console or with aws ec2 modify-volume, then run sudo growpart /dev/nvme0n1 3 && sudo xfs_growfs / (or reboot).
• Swap. The image has no swap. Add a swap file yourself if your workload needs one.
• AIDE. The file integrity database is built from the image's own files, and the CIS profile schedules aide --check daily at 04:05 from /etc/crontab.

Step 13: Install software and add users

The instance uses the standard CentOS Stream 10 repositories (BaseOS, AppStream and Extras):

sudo dnf -q list --available nginx

Expected output (the version changes over time):

Available Packages
nginx.x86_64                     2:1.26.3-15.el10                      appstream

Install and start software in the usual way, for example sudo dnf -y install nginx then sudo systemctl enable --now nginx, and open its port in the security group and firewalld (Step 8). The CRB repository (build and development dependencies) is installed but disabled; enable it with sudo dnf config-manager --set-enabled crb if a package needs it. The AWS CLI is not on the image; install the current version from AWS (the AWS CLI install guide) if you need it.

To add another administrator, create the account, add it to the wheel group and give it an SSH key:

sudo useradd -m -G wheel alice
sudo install -d -m 700 -o alice -g alice /home/alice/.ssh
echo "ssh-ed25519 AAAA... alice@laptop" | sudo tee /home/alice/.ssh/authorized_keys
sudo chown alice:alice /home/alice/.ssh/authorized_keys && sudo chmod 600 /home/alice/.ssh/authorized_keys
sudo restorecon -R /home/alice/.ssh

Because SSH is key-only, a new account needs its key in authorized_keys (and restorecon gives the file the SELinux label sshd expects). The new account has no password, so sudo cannot authenticate it until you give it one with sudo passwd alice. SSH stays key-only; the password is used by sudo. (Only ec2-user, created by cloud-init, has password-free sudo.)

Common use cases

• Developing and testing against what the next RHEL 10 minor release will contain, before it ships
• Building and validating software, packages and automation for the RHEL 10 family on a free distribution
• A base for workloads that must show CIS Level 1 alignment, with the evaluation report already on the machine
• Fleets managed through Systems Manager, with IMDSv2 required from the first boot
• A starting point for your own golden image: add your software, re-run Step 6, and keep the report with your build

Troubleshooting

SSH says "Too many authentication failures"

The SSH server allows four authentication attempts per connection. If your SSH agent holds several keys, it can use them up before it offers the right one. Tell SSH to offer only the key you name:

ssh -o IdentitiesOnly=yes -i ~/.ssh/my-key-pair.pem ec2-user@<public-ip>

Cannot connect via SSH

1. Check the instance is running and has passed its status checks.
2. Check the security group allows TCP 22 from your current public address.
3. Use the user name ec2-user and the key pair chosen at launch. Password login is disabled, so a wrong key never falls back to a password prompt.
4. If you changed firewalld, make sure the ssh service is still allowed. Session Manager (Step 2) still works if SSH is blocked, provided the instance has a Systems Manager instance profile.

The instance does not boot on an older instance type

CentOS Stream 10 for x86_64 is built for the x86-64-v3 feature level. Very old instance families whose processors lack AVX2 cannot run it; choose a current-generation type such as m5, m6i, m7i, c6i or t3.

My service is running but not reachable

Allow the port in both the security group and firewalld (Step 8). sudo firewall-cmd --list-all shows the firewalld rules; sudo ss -tlnp shows whether the service listens on all addresses or only on loopback. If the service runs on a non-standard port, SELinux may also need to allow it: install the SELinux management tools with sudo dnf -y install policycoreutils-python-utils, then, for example, sudo semanage port -a -t http_port_t -p tcp 8080 for a web server on 8080.

A tool that uses instance metadata fails

The image requires IMDSv2. Old scripts that call http://169.254.169.254/ without a token get HTTP 401. Update them to request a token first (Step 7), or use the AWS CLI or a current SDK.

An automatic update changed something

dnf-automatic applies every update daily (Step 10). See what changed and when with sudo dnf history list and sudo dnf history info <id>; sudo dnf history undo <id> reverses a transaction while the older packages are still in the repositories.

Package manager issues

Refresh the metadata first:

sudo dnf -q makecache --refresh && echo "repository metadata refreshed"

If the repositories are unreachable, check that the instance has outbound internet access (a public IP or a NAT gateway) and that DNS resolves:

getent hosts mirrors.centos.org

Important notes

CentOS Stream is free and open source software. It is a distribution of thousands of packages, each under its own licence (GPL, LGPL, MIT, BSD, Apache 2.0 and others); rpm -qi <package> shows each package's licence. No subscription or licence key is needed to run this image. The compliance tooling is OpenSCAP (LGPL 2.1 or later) and SCAP Security Guide content (BSD 3-Clause, licence text in /usr/share/doc/cloudimg/scap-security-guide-LICENSE.txt).

CentOS Stream 10 is maintained by the CentOS Project for the life of Red Hat Enterprise Linux 10's full support phase; the CentOS Project publishes the end-of-life date. It is a continuously updated distribution that runs slightly ahead of RHEL 10, so it is not a drop-in replacement for a specific RHEL release.

The CIS Level 1 Server profile used here is the OpenSCAP profile published in SCAP Security Guide. These images are not CIS Hardened Images and are not certified by the Center for Internet Security. A pass rate measures this image as built; your own changes affect it, which is why the evaluation can be re-run (Step 6).

CentOS is a trademark of Red Hat, Inc. Red Hat Enterprise Linux is a trademark of Red Hat, Inc. CIS is a trademark of the Center for Internet Security. These names are used only to identify the software, its compatibility and the profile. cloudimg is not affiliated with or endorsed by the CentOS Project, Red Hat or the Center for Internet Security.

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• CentOS Stream on AWS hub: www.cloudimg.co.uk/guides/centos-stream-aws