Why a `nice -1` Triggered an Alarm — And Why MX Linux Did It On Purpose

By Khawar Nehal

The Curious Case of the Negative Nice Value

While debugging system performance on my MX Linux desktop, I ran a routine command:

ps axo pid,ni,comm | grep -E 'firefox|thunderbird'

To my surprise, the output showed:

  45956  -1 firefox-bin
1139493  -1 thunderbird

Both Firefox and Thunderbird were running with a nice value of –1—a higher-than-default scheduling priority. On most Linux systems, regular users cannot set negative nice values without root privileges. So why were these user-space applications running at elevated priority? And more importantly—should this be a cause for concern?

At first glance, it looked like a misconfiguration, a security anomaly, or even a sign of privilege escalation. But the truth is far more benign—and intentional.

Understanding `nice`: A Quick Primer

In Linux, the nice value determines a process’s CPU scheduling priority:

Range: –20 (highest priority) to +19 (lowest priority)
Default for new processes: 0
Only privileged users (root or those with CAP_SYS_NICE) can set negative nice values—unless explicitly allowed.

So when unprivileged processes appear with nice = -1, it raises eyebrows. After all, shouldn’t the kernel block this?

Not if the system administrator—or your Linux distribution—says otherwise.

MX Linux: Performance by Design

MX Linux, a lightweight Debian-based distro built for responsiveness and stability, deliberately configures user sessions to allow and apply a mild priority boost to interactive desktop applications.

This isn’t a bug, a hack, or a security flaw—it’s a user experience optimization.

Why `nice = -1`?

The choice of –1 is subtle but significant:

It’s just enough to give GUI apps (browsers, email clients, terminals) slightly better CPU access under system load.
It avoids the pitfalls of aggressive prioritization (e.g., starving background tasks).
On older or resource-constrained hardware—MX Linux’s target audience—this small tweak makes the system feel noticeably snappier.

As the MX Linux team puts it: "Responsiveness matters more than theoretical fairness."

How Does MX Linux Achieve This?

Two mechanisms work together:

1. PAM Limits Configuration

A file like /etc/security/limits.d/mx-nice.conf grants users the right to use negative nice values:

# /etc/security/limits.d/mx-nice.conf
* soft priority 1
* hard priority 1

Here, priority 1 means the user can set nice values down to –1 (since nice = -priority).

This relaxes the default restriction (ulimit -e = 0) and sets ulimit -e = 1 (or higher—in some cases, up to 30, as seen in our tests).

2. Session Initialization Scripts

During X11 session startup, MX Linux (inheriting from antiX) may run scripts that renice the user session:

# Conceptual example (may exist in /etc/X11/Xsession.d/)
renice -n -1 $$

This ensures that all child processes launched from the desktop—including Firefox, Thunderbird, LibreOffice, etc.—inherit nice = -1.

Why Did This Trigger an “Alarm”?

For system administrators or security-conscious users, seeing unexpected negative nice values can raise red flags:

Security: Could malware be elevating its priority?
Compliance: Does this violate hardening policies?
Stability: Will high-priority processes starve critical services?

In most enterprise or server environments, any deviation from default scheduling is suspect. But on a single-user desktop OS optimized for interactivity, the calculus changes.

MX Linux prioritizes human experience over strict POSIX neutrality—and for good reason.

Should You Be Concerned?

Almost certainly not. Here’s why:

The priority boost is minimal (-1 vs. -20).
It applies only to your own user processes—no system-wide impact.
Background tasks (cron jobs, daemons, downloads) remain at nice ≥ 0.
MX Linux has used this approach for years with no reported stability issues.

In fact, if you disable it, you might notice your system feels slightly less responsive during multitasking—especially on machines with 2–4 GB RAM or older CPUs.

How to Verify or Disable It (If You Must)

Check your limits:

ulimit -e  # Returns 1 or higher on MX Linux

Locate the config:

ls /etc/security/limits.d/*nice*
cat /etc/security/limits.d/mx-nice.conf

Temporarily test without it:
Log into a TTY (Ctrl+Alt+F2). Run ps -o ni= -p $$—you’ll likely see 0. The effect is desktop-session-only.

To disable:
Rename the config file:

sudo mv /etc/security/limits.d/mx-nice.conf ~/mx-nice.conf.disabled

Then log out and back in.

But ask yourself: Do I really want to sacrifice responsiveness for theoretical purity?

Conclusion: A Thoughtful Trade-Off

The nice = -1 you see isn’t a flaw—it’s a signature of MX Linux’s philosophy: optimize for the human at the keyboard.

In a world where bloated operating systems demand ever-more resources, MX Linux’s subtle tuning reminds us that small, intelligent defaults can make a big difference.

So the next time you see a negative nice value on your MX desktop, don’t sound the alarm.
Tip your hat to the engineers who made your browser feel just a little faster.