Can htop Display Effective User ID Versus Real User ID?

This article explores whether the htop process viewer can distinguish between effective and real user IDs on Ubuntu. While htop is a powerful tool for monitoring system resources, it has limitations regarding specific user identity details. We will examine its default capabilities and provide alternative commands for viewing detailed user ID information.

Understanding htop User Columns

By default, htop displays the user name associated with each running process in the USER column. This name corresponds to the effective user ID (EUID). The effective user ID determines the access permissions the process has while running. For most standard monitoring tasks, knowing the effective user is sufficient to identify who owns the process and what resources it can access.

Limitations Regarding Real User ID

htop does not natively support a column to display the real user ID (RUID) separately from the effective user ID. The real user ID identifies the user who originally launched the process, which may differ from the effective user ID if the program uses setuid permissions. Because htop focuses on resource usage rather than security auditing, it simplifies this information to show only the effective user.

Alternative Methods for Ubuntu Users

To view both the real and effective user IDs on Ubuntu, you should use the ps command. Running ps -eo pid,ruid,euid,user in the terminal will list the process ID, real user ID, effective user ID, and user name for all processes. Another method is to inspect the status file directly by reading /proc/[pid]/status, which contains detailed fields for Uid and Gid showing real, effective, saved, and filesystem IDs. These tools provide the granular security data that htop omits.