Tuning profiles with tuned, and time with chrony

tuned: performance profiles

A server can be tuned for different goals: fast database queries, low power use, or a virtual machine sharing a host. There are hundreds of kernel and disk settings behind these goals. tuned is a service that groups the settings into profiles, so you pick a goal instead of changing each setting by hand.

# dnf install -y tuned        # usually already installed
# systemctl enable --now tuned
# tuned-adm active
Current active profile: virtual-guest
# tuned-adm recommend
virtual-guest
# tuned-adm list
Available profiles:
- balanced                    - General non-specialized tuned profile
- powersave                   - Optimize for low power consumption
- throughput-performance      - Broadly applicable tuning that provides excellent performance across a variety of common server workloads
- virtual-guest               - Optimize for running inside a virtual guest
- virtual-host                - Optimize for running KVM guests
...
# tuned-adm profile throughput-performance
# tuned-adm verify
Verification succeeded, current system settings match the preset profile.

tuned-adm recommend looks at the machine (for example, is it a VM?) and suggests a profile. In exams a task may say "set the recommended tuned profile"; run recommend and then profile with its answer. The profile is remembered across reboots as long as the tuned service is enabled.

Why time must be right

Wrong time causes real trouble: log lines from different servers cannot be matched, TLS certificates look "not yet valid" or "expired", Kerberos and Active Directory logins fail when clocks differ by more than a few minutes, and scheduled jobs run at the wrong hour. NTP (Network Time Protocol) keeps clocks in sync with time servers. On RHEL the NTP client is chronyd, from the chrony package.

$ timedatectl
               Local time: Mon 2026-10-19 11:20:31 IST
           Universal time: Mon 2026-10-19 05:50:31 UTC
                 Time zone: Asia/Kolkata (IST, +0530)
System clock synchronized: yes
              NTP service: active
# timedatectl set-timezone Asia/Kolkata
# timedatectl list-timezones | grep Kolkata
Asia/Kolkata

Configuring chrony

The settings are in /etc/chrony.conf. A server or pool line names a time source. iburst sends a quick burst of requests at start-up so the clock syncs faster. After changes, restart chronyd and check the sources.

# grep -E '^(server|pool)' /etc/chrony.conf
pool 2.rhel.pool.ntp.org iburst
# vim /etc/chrony.conf           # replace with your company's NTP server:
server ntp.example.com iburst
# systemctl restart chronyd
# chronyc sources -v
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* ntp.example.com               2   6    17    12   +215us[ +301us] +/-   18ms

In India, public NTP servers include pools such as in.pool.ntp.org, and many companies run their own internal NTP servers. Use what your network team gives you; production servers often cannot reach the internet.

Common mistakes

• Editing /etc/chrony.conf and forgetting to restart chronyd. Check with chronyc sources.
• Changing the time zone and thinking the clock is now "fixed". The time zone only changes how time is shown; sync is a separate thing.
• Choosing a tuned profile by guesswork. Use tuned-adm recommend unless you have a measured reason.
• Leaving the firewall closed on an NTP SERVER you set up (UDP port 123). Clients only need outgoing access.